Carbon Contamination – Science Papers

ABSTRACT:
Grafted copolymers of chitosan–vinylpyrrolidone, water-soluble at a pH of 6.8–7.5, were obtained. A technique has been developed for obtaining an aggregatively stable system of platinum nanoparticles in copolymer solutions with an average size of ~4 nm. The thermophysical and structural characteristics of the powdered composition of a platinum nanoparticle-copolymer are investigated. An in vitro comparison of the antitumor activity of solutions of the developed composition and cisplatin at the same platinum concentration was performed. It was found that with respect to the culture of HeLa Kyoto and A431 cancer cells, the composition is five and two times less effective than cisplatin, respectively. Along with this, the biocompatibility of the composition is 17 times higher than that of cisplatin, which allows its use at elevated concentrations and the development of an antitumor agent with platinum nanoparticles commensurate in effectiveness with cisplatin.

ABSTRACT:
Ternary In-Sn-Bi alloys exhibit potentially superior superconducting properties compared to other lead-free solders, making them promising candidates for replacing lead-based solders in superconducting joints. In this work, the microstructure and superconducting properties of In-15wt.%Bi-35wt.%Sn and In-23wt.%Bi-27wt.%Sn were studied and compared with samples containing 0.5 wt.% and 1 wt.% Ga addition. The study reveals significant modifications in the microstructure with the addition of Ga, resulting in a slight decay in superconducting properties when higher levels of liquid Ga are present in the microstructure. Moreover, the difference in superconducting properties between the two In-Bi-Sn compositions is negligible, despite different microstructures. The highest critical temperature of 6.76 K was achieved in In-23wt.%Bi-27wt.%Sn. The tested superconducting properties including critical temperature (Tc ), critical current density (Jc ) and critical magnetic field strength (H c ) are discussed with respect to pinning mechanisms and microstructures based on electron backscatter diffraction (EBSD) and x-ray diffraction (XRD) results.

ABSTRACT:
Spiropyran is a dynamic organic compound that is distinguished by its reversible conversion between two forms: the colorless closed spiropyran (SP) form and the purple open merocyanine (MC) form. Typically triggered by UV light and reversed by visible light, spiropyran-functionalized surfaces offer reversible conversion in properties including color, polarity, reactivity, and fluorescence, making them applicable to diverse applications in chemical sensors, biosensors, drug delivery, and heavy metal extraction. While spiropyran has been successfully incorporated into various material platforms with SiO 2 surfaces, its application on flat surfaces has been limited due to surface area constraints and a lack of standardized evaluation methods, which largely depend on the integration approach and substrate type used. In this study, we systematically review the existing literature and categorize integration methods and substrate types first and then report on our experimental work, in which we developed a streamlined three-step immobilization protocol, which includes surface activation, amination with (3-aminopropyl) triethoxysilane (APTES), and subsequent functionalization with carboxylic spiropyran (SP-COOH). Using SiO 2 surfaces as a demonstration, we have also established a robust characterization protocol, consisting of contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and fluorometric analysis. Our results evaluate the newly developed immobilization protocol, demonstrating effective activation and optimal amination using a 2% APTES solution, achieved in 5 min at room temperature. Fluorescence imaging provided clear contrast between the SP and the MC forms. Furthermore, we discuss limitations in the surface density of functional groups and steric hindrance and propose future improvements. Our work not only underscores the versatility of spiropyran in surface patterning but also provides optimized protocols for its immobilization and characterization on SiO 2 surfaces, which may be adapted for use on other substrates. These advancements lay the groundwork for on-chip sensing technologies and other applications.

ABSTRACT:
In-situ experimental techniques are essential for understanding the deformation evolution of materials by enabling real-time tracking of microstructure changes. This study employs in-situ electron backscatter diffraction (EBSD), high-resolution digital image correlation (HR-DIC), and in-situ neutron diffraction to investigate the deformation mechanism of IN690. The results reveal that the geometrically necessary dislocation (GND) density does not increase during elastic deformation but exhibits a linear increase during plastic deformation when the strain is less than 10%. Initially, during the onset of plastic deformation, GND density primarily accumulates along grain boundaries, with high-density areas developing within grains as deformation progresses. Careful analysis shows that the free surface effect during deformation does not impact GND density measurements. High resolution digital image correlation (HR-DIC) shear strain maps demonstrate local strain heterogeneity, with long and intense slip traces observed near twin boundaries and an increase in number and intensity of slip traces as deformation progresses. In-situ neutron diffraction indicates that the total dislocation density of IN690, which includes statistically stored dislocations (SSD) and remains unchanged during elastic deformation and increases linearly during plastic deformation. The GND density measured by EBSD constitutes less than 7% of the total dislocation density measured by neutron diffraction.

ABSTRACT:
The work functions of two polar surfaces of ZnO (wurtzite), i.e., O-(000–1) and Zn-(0001) are determined by photoelectron spectroscopy in ultrahigh vacuum or in the presence of oxygen or water vapor at near-ambient pressures, and by Kelvin probe in air. The work functions were also determined by Mott-Schottky analysis in aqueous or aprotic (acetonitrile) electrolyte solutions. The values obtained by different techniques and in different environments are much less scattered compared to the fluctuations, reported for TiO 2 (anatase or rutile). The Zn-(0001) surface has a smaller work function for all the solid/vacuum and solid/gas interfaces, and also in the acetonitrile electrolyte solution. Solely at the aqueous electrochemical interface, the difference is small or even opposite. We propose a hypothesis that the dissociative water adsorption on the O-(000–1) is responsible for this irregular downshift of the work function in aqueous medium.

ABSTRACT:
Twisted 2D material heterostructures provide an exciting platform for investigating new fundamental physical phenomena. Many of the most interesting behaviours emerge at small twist angles, where the materials reconstruct to form areas of perfectly stacked crystal separated by partial dislocations. However, understanding the properties of these systems is often impossible without correlative imaging of their local reconstructed domain architecture, which exhibits random variations due to disorder and contamination. Here we demonstrate a simple and widely accessible route to visualise domains in as-produced twisted transition metal dichalcogenide (TMD) heterostructures using electron channelling contrast imaging (ECCI) in the scanning electron microscope (SEM). This non-destructive approach is compatible with conventional substrates and allows domains to be visualised even when sealed beneath an encapsulation layer. Complementary theoretical calculations reveal how a combination of elastic and inelastic scattering leads to contrast inversions at specified detector scattering angles and sample tilts. We demonstrate that optimal domain contrast is therefore achieved by maximising signal collection while avoiding contrast inversion conditions.

ABSTRACT:
The 8.4 eV nuclear isomer state in Th-229 is resonantly excited in Th-doped CaF 2 crystals using a tabletop tunable laser system. A resonance fluorescence signal is observed in two crystals with different Th-229 dopant concentrations, while it is absent in a control experiment using Th-232. The nuclear resonance for the Th 4 þ ions in Th:CaF 2 is measured at the wavelength 148.3821(5) nm, frequency 2020.409(7) THz, and the fluorescence lifetime in the crystal is 630(15) s, corresponding to an isomer half-life of 1740(50) s for a nucleus isolated in vacuum. These results pave the way toward Th-229 nuclear laser spectroscopy and realizing optical nuclear clocks.
 
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ABSTRACT:
A novel iron oxide nanoparticlc (Fe 3 0 4 @C-S 0 3 H) fabricated with carbon and sulfonic acid was prepared w,ing the concept of green chemistTy protocol. The usage of agro-waste extract for core -shell Fe 3 0 4 preparation and its biochar powder a.<;a carbon source for the fabrication of the catalyst was the dual benefit. T his prepared catalyst was employed for the synthesis of 4H-chromene derivative via a three-componen t one-pot reaction of resorcinol, aryl aldehyde , and malononitrile in ethanol under microwave irradiation. The method was found to be nontoxic, inexpensive, faster, and simple work-up with greener solvent, and gave excellent product isolation with about 91 % yield in 4 min microwave irradiation in the presence of 25 mg catalyst. The catalyst could be recovered after the reaction by an elttemal magnet and reused for up to four runs without any considerable loss in its catalytic activity. The prepared catalyst was characterized by Ff -TR, and prominent bands were observed for surface functionalization. The XRD data revealed prominent peaks for the formation ofFe 3 0 4 @C-S 0 3 H, and the results arc comparable with the reported literature; the VSM data gives a clear idea about the magnetic nature of the catalyst and respective surface-modified core shells, the surface morphology, and the required elements present are confirmed by FE-SEM and EDX . TGA admits that the thermal stability of the catalyst is up to 600 °C under a nitrogen atmosphere. The 1 H- & 13 C-NMR and LC-MS analysis arc explored for the analysis of the fonnation of final 2-arnino-4H-chromene derivatives. Further antimicrobial activities of the selected compounds were performed, and the results arc promising and comparable with the reference.

ABSTRACT:
We report the simple method of fabrication, self-supported nanostructure of Co – P – O nanoparticles (NPs) on carbon cloth scaffold by electroless plating. Co – P – O demonstrates exceptional bi-functional catalytic performance in water electrolysis, efficiently producing hydrogen (H 2 ) and oxygen (O ) gases simultaneously due to optimized adsorption energy for intermediates and the excellent conductivity of2 Cobalt-metallic nanoparticles. Co – P – O achieves a geometric current of 10 mA/cm 2 with 190 mV and 280 mV overpotential for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, while its continuous catalytic nanoparticle coating on the carbon cloth scaffold ensures superior charge transport with minimal resistance. It is highly encouraging to observe that the HER and OER performance of Co – P – O electrodes far surpasses that of carbon cloth, approaching the benchmark set by noble electrocatalysts Pt/C and RuO 2 . The alkaline electrolyser based on the two-electrode cell using Co – P – O electrodes demonstrates bi-functional water splitting at 1.64 V and 1.98 V at 10 and 100 mA/cm 2 . Furthermore, the alkaline electrolyser exhibits stable electrocatalytic activity for about more than 16 h at the current density of 50 mA/cm 2 .

ABSTRACT:
Sulforaphane, an organosulfur phytochemical, has been demonstrated to have significant anticancer potential in both in vitro and in vivo studies, exhibiting mechanisms of action that include inducing apoptosis, inhibiting cell proliferation, and modulating key signalling pathways involved in cancer development. However, its instability presents a major obstacle to its clinical application due to its limited bioavailability. This study aimed to improve the stability and thus the bioavailability of sulforaphane from broccoli by microencapsulation with whey (BW) and pea protein (BP) by freeze-drying. BW and BP were characterised by particle size measurement, colour, infrared spectroscopy, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. Dynamic in vitro gastrointestinal digestion was performed to measure sulforaphane bioaccessibility, in BP, BW and dried broccoli. A Caco-2-HT29-MTX-E12 intestinal absorption model was used to measure sulforaphane bioavailability. The in vitro dynamic gastrointestinal digestion revealed that sulforaphane bioaccessibility of BW was significantly higher (67.7 ± 1.2%) than BP (19.0 ± 2.2%) and dried broccoli (19.6 ± 10.4%) (p < 0.01). In addition, sulforaphane bioavailability of BW was also significantly greater (54.4 ± 4.0%) in comparison to BP (9.6 ± 1.2%) and dried broccoli (15.8 ± 2.2%) (p < 0.01). Microencapsulation of broccoli sulforaphane with whey protein significantly improved its in vitro bioaccessibility and bioavailability. This suggests that whey protein isolate could be a promising wall material to protect and stabilise sulforaphane for enhanced bioactivity and applications (such as nutraceutical formulations).

ABSTRACT:
We present a new set of reference materials, the ND70-series, for in situ measurement of volatile elements (H2 O, CO2 , S, Cl, F) in silicate glass of basaltic composition. The materials were synthesised in piston cylinders at pressures of 1 to 1.5 GPa under volatileundersaturated conditions. They span mass fractions from 0 to 6% m/m H2 O, from 0 to 1.6% m/m CO 2 and from 0 to 1% m/m S, Cl and F. The materials were characterised by elastic recoil detection analysis for H2 O, by nuclear reaction analysis for CO2 , by elemental analyser for CO2 , by Fourier transform infrared spectroscopy for H2 O and CO2 , by secondary ion mass spectrometry for H2 O, CO2 , S, Cl and F, and by electron probe microanalysis for CO2 , S, Cl and major elements. Comparison between expected and measured volatile amounts across techniques and institutions is excellent. It was found however that SIMS measurements of CO 2 mass fractions using either Cs + or O − primary beams are strongly a×ected by the glass H2 O content. Reference materials have been made available to users at ion probe facilities in the US, Europe and Japan. Remaining reference materials are preserved at the Smithsonian National Museum of Natural History where they are freely available on loan to any researcher.

ABSTRACT:
Meticulous sample preparation and strict adherence to preservation procedures are essential for electron microscopy investigations, which enable accurate capture of organisms’ morphology, size, and potential interactions within the sample. Here, we present a protocol for preserving cells of the model diatom Phaeodactylum tricornutum and its native bacterial community. We describe steps for diatom fixation and coverslip preparation and washing. We then detail procedures for dehydrating, drying, and metallizing samples followed by observation using scanning electron microscopy.
 
 
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ABSTRACT:
Composites from 2D nanomaterials show uniquely high electrical, thermal and mechanical properties1,2 . Pairing their robustness with polarization rotation is needed for hyperspectral optics in extreme conditions3,4 . However, the rigid nanoplatelets have randomized achiral shapes, which scramble the circular polarization of photons with comparable wavelengths. Here we show that multilayer nanocomposites from 2D nanomaterials with complex textured surfaces strongly and controllably rotate light polarization, despite being nano-achiral and partially disordered. The intense circular dichroism (CD) in nanocomposite films originates from the diagonal patterns of wrinkles, grooves or ridges, leading to an angular offset between axes of linear birefringence (LB) and linear dichroism (LD). Stratification of the layer-by-layer (LBL) assembled nanocomposites affords precise engineering of the polarization-active materials from imprecise nanoplatelets with an optical asymmetry g-factor of 1.0, exceeding those of typical nanomaterials by about 500 times. High thermal resilience of the composite optics enables operating temperature as high as 250 °C and imaging of hot emitters in the near-infrared (NIR) part of the spectrum. Combining LBL engineered nanocomposites with achiral dyes results in anisotropic factors for circularly polarized emission approaching the theoretical limit. The generality of the observed phenomena is demonstrated by nanocomposite polarizers from molybdenum sulfide (MoS 2 ), MXene and graphene oxide (GO) and by two manufacturing methods. A large family of LBL optical nanocomponents can be computationally designed and additively engineered for ruggedized optics.

ABSTRACT:
The observation of photosynthetic biofilms growing on the Fine Residue Deposit (FRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa suggests that processed kimberlite supports bacterial growth. The presence of this biofilm may aid in the acceleration of weathering of this ultra-mafic host material – a process that can sequester CO 2 via carbon mineralization. Laboratory and field trial experiments were undertaken to understand the microbe–mineral interactions occurring in these systems, and how these interactions impact geochemical cycling and carbonate precipitation. At laboratory scale it was discovered that using kimberlite as a growth supplement increased biomass production (up to 25-fold) and promoted microbiome diversity, while the inoculation of FRD systems aided in the aggregation, settling, and dewatering of kimberlitic slurries. Field trial studies combining photosynthetic biofilms (cultured in 3 × 1,000 L bioreactors) with FRD material were initiated to better understand microbially enhanced mineral carbonation across different depths, and under field environmental conditions. Over the 15-month experiment the microbial populations shifted with the kimberlitic environmental pressure, with the control and inoculated systems converging. The natural endogenous biosphere (control) and the inoculum accelerated carbonate precipitation across the entire 40 cm bioreactor depth, producing average 15-month carbonation rates of 0.57 wt.% and 1.17 wt.%, respectively. This corresponds to an annual CO2 e mine offset of ~4.48% and ~ 9.2%, respectively. Millimetre-centimetre scale secondary carbonate that formed in the inoculated bioreactors was determined to be biogenic in nature (i.e., possessing microbial fossils) and took the form of radiating colloform precipitates with the addition of new, mineralized colonies. Surficial conditions resulted in the largest production of secondary carbonate, consistent with a ca. 12% mine site CO2 e annual offset after a 15-month incubation period.

ABSTRACT:
Direct fabrication of pure metallic nanostructures is one of the main aims of focused electron beam-induced deposition (FEBID). It was recently achieved for gold deposits by the co-injection of a water precursor and the gold precursor Au(tfac)Me 2 . In this work results are reported, using the same approach, on a different gold precursor, Au(acac)Me 2 , as well as the frequently used platinum precursor MeCpPtMe 3 . As a water precursor MgSO 4 ·7H 2 O was used. The purification during deposition led to a decrease of the carbon-to-gold ratio (in atom %) from 2.8 to 0.5 and a decrease of the carbon-to-platinum ratio (in atom %) from 6–7 to 0.2. The purification was done in a regular scanning electron microscope using commercially available components and chemicals, which paves the way for a broader application of direct etching-assisted FEBID to obtain pure metallic structures.

ABSTRACT:
Nanoceria (NC) are widely studied as potent nanozyme antioxidants, featuring unique multifunctional, self-regenerative, and high-throughput enzymatic functions. However, bare NC are reported to show poor colloidal stability in biological media. Despite this, the nexus between colloidal stability and antioxidant activity has rarely been assessed. Here, a library of three copolymeric stabilising agents was synthesised, each consisting of hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) brushes (P(OEGMA)) and a novel catechol anchoring block, and used for surface engineering of NC. The colloidal stability of the surface-engineered NC was assessed in phosphate buffered saline (PBS) by monitoring their precipitation via UV-Vis spectrophotometry, and their catalase (CAT)- and superoxide dismutase (SOD)-like activities were analysed using fluorospectrophotometry. The obtained results indicate that P(OEGMA) coating improves colloidal stability of NC over 48 h, highlighting the stable attachment of catechol functionalities to the surface of NC. In addition, X-ray photoelectron spectroscopy (XPS) indicates that the catechol functionalities lead to an increase in Ce3+ /Ce 4+ ratio and the concentration of oxygen vacancies, depending on the number of catechol units. Altogether, surface engineering of NC optimally results in an increase in CAT- and SOD-like activities by, respectively, 41% (=57.7% H2 O 2 elimination) and 78% (=78.0% O 2 •− elimination) relative to bare NC, signifying a positive correlation between colloidal stability and antioxidant activity of the NC nanozymes.

ABSTRACT:
The chemical bath deposition (CBD) process enables the deposition of ZnO nanowires (NWs) on various substrates with customizable morphology. However, the hydrogen-rich CBD environment introduces numerous hydrogen-related defects, unintentionally doping the ZnO NWs and increasing their electrical conductivity. The oxygen-based plasma treatment can modify the nature and amount of these defects, potentially tailoring the ZnO NW properties for specific applications. This study examines the impact of the average ion energy on the formation of oxygen vacancies (V O ) and hydrogen-related defects in ZnO NWs exposed to low-pressure oxygen plasma. Using X-ray photoelectron spectroscopy (XPS), 5 K cathodoluminescence (5K CL), and Raman spectroscopy, a comprehensive understanding of the effect of the oxygen ion energy on the formation of defects and defect complexes was established. A series of associative and dissociative reactions indicated that controlling plasma process parameters, particularly ion energy, is crucial. The XPS data suggested that increasing the ion energy could enhance Fermi level pinning by increasing the amount of V O and favoring the hydroxyl group adsorption, expanding the depletion region of charge carriers. The 5K CL and Raman spectroscopy further demonstrated the potential to adjust the ZnO NW physical properties by varying the oxygen ion energy, affecting various donor- and acceptor-type defect complexes. This study highlights the ability to tune the ZnO NW properties at low temperature by modifying plasma process parameters, offering new possibilities for a wide variety of nanoscale engineering devices fabricated on flexible and/or transparent substrates.

ABSTRACT:
The heterogeneous photocatalysis of organic dyes using ZnO nanowires (NWs) is of high interest to face the challenge of eco-eÕcient water remediation. However, the e×ects of the wurtzite structure of ZnO and hence of the shape of nanostructures on the photocatalytic processes are still under debate. Herein, it is shown that the photocatalytic activity of ZnO single crystals with Òve di×erent orientations follows a pseudo-Òrst-order kinetics as: (000 ¯1) < {10 ¯1 2} < {20 ¯2 1} < {10 ¯1 0} < (0001). The photocatalytic processes are independent of the nature of the crystallographic planes, apart from the semipolar {20 ¯2 1} orientation. Interestingly, ZnO NWs exhibit a photocatalytic activity that is relatively independent of their length, which is neither due to the penetration of organic dyes nor to the penetration of UV light. Instead, the sidewalls of ZnO NWs are much less eÕcient than the ZnO single crystal with the same nonpolar m-plane orientation, indicating that the structural morphology and chemical composition of the surface, as well as their much higher doping level, govern the photocatalytic activity and processes. These Òndings indicate that the increase in the photocatalytic activity of ZnO NWs should be addressed by designing more active surfaces rather than simply increasing their total surface area.

ABSTRACT:
The behavior of catalytic particles depends on their chemical structure and morphology. To reveal this information, the characterization with atom probe tomography has huge potential. Despite progresses and papers proposing various approaches towards the incorporation of particles inside atom probe tips, no single approach has been broadly applicable to date. In this paper, we introduce a workflow that allowed us to prepare atom probe specimens from Ga particles in suspension in the size range of 50 nm up to 2 μ m. By combining dielectrophoresis and electrodeposition in a suitable way, we achieve a near-tip shape geometry, without a time-consuming FIB lift-out. This workflow is a simple and quick method to prepare atom probe tips and allows for a high preparation throughput. Also, not using a lift-out allowed us to use a cryo-stage, avoiding melting of the Ga particles, while ensuring a mechanical stable atom probe tip. The specimen prepared by this workflow enable a stable measurement and low fracture rates.

ABSTRACT:
The remarkable physical properties of dental enamel can be largely attributed to the structure of the hydroxyapatite (HAp) crystallites on the sub-micrometre scale. Characterising the HAp microstructure is challenging, due to the nanoscale of individual crystallites and practical challenges associated with HAp examination using electron microscopy techniques. Conventional methods for enamel characterisation include imaging using transmission electron microscopy (TEM) or specialised beamline techniques, such as polarisation-dependent imaging contrast (PIC). These provide useful information at the necessary spatial resolution but are not able to measure the full crystallographic orientation of the HAp crystallites. Here we demonstrate the effectiveness of enamel analyses using transmission Kikuchi diffraction (TKD) in the scanning electron microscope, coupled with newly-developed pattern matching methods. The pattern matching approach, using dynamic template matching coupled with subsequent orientation refinement, enables robust indexing of even poor-quality TKD patterns, resulting in significantly improved data quality compared to conventional diffraction pattern indexing methods. The potential of this method for the analysis of nanocrystalline enamel structures is demonstrated by the characterisation of a human enamel TEM sample and the subsequent comparison of the results to high resolution TEM imaging. The TKD – pattern matching approach measures the full HAp crystallographic orientation enabling a quantitative measurement of not just the c-axis orientations, but also the extent of any rotation of the crystal lattice about the c-axis, between and within grains. Results presented here show how this additional information highlights potentially significant aspects of the HAp crystallite structure, including intra-crystallite distortion and the presence of multiple high angle boundaries between adjacent crystallites with rotations about the c-axis. These and other observations enable a more rigorous understanding of the relationship between HAp structures and the physical properties of dental enamel.

ABSTRACT:
The development of the super-lyophilic surface has gained tremendous attention due to its wide applications in the industrial and engineering fields. However, there are still challenges in preparing super-amphiphilic surfaces, especially microstructure surfaces. This study reports the progress of fabricating the super -amphiphilic microgroove surface (SAMS) for multi-purposes via physical and chemical modification. First, the microgroove structure is achieved via the fused deposition modeling 3D printing method with layer-by-layer (XZ direction) printing; then, the surface chemical composition is adjusted via a low-pressure argon plasma treatment. Besides, the surface roughness factor and the hydroxyl group content are controlled via the printed layer height/nozzle diameter ratio and plasma treatment time to optimize the capillary force between grooves to obtain the most appropriate SAMS. The achieved SAMS shows the versatile ability to wick common solvents of various polarities, including carbon tetrach loride, ethylene glycol, ethanol, 1-decanol, hexane, and water. The wicking dynamic of liquids on SAMS fits well with Washburn’s model at the initial stage, but it gradually moves out of the model. The simple and cost-efficient manufacturing process of SAMS can be scaled up for industrial applications like microfluidic and solvent recovery.

ABSTRACT:
Multiple immune pathways in humans conjugate ubiquitin-like proteins to virus and host molecules as a means of antiviral defense. Here we studied an anti-phage defense system in bacteria, comprising a ubiquitin-like protein, ubiquitin-conjugating enzymes E1 and E2, and a deubiquitinase. We show that during phage infection, this system specifically conjugates the ubiquitin-like protein to the phage central tail fiber, a protein at the tip of the tail that is essential for tail assembly as well as for recognition of the target host receptor. Following infection, cells encoding this defense system release a mixture of partially assembled, tailless phage particles, and fully assembled phages in which the central tail fiber is obstructed by the covalently attached ubiquitin-like protein. These phages exhibit severely impaired infectivity, explaining how the defense system protects the bacterial population from the spread of phage infection. Our findings demonstrate that conjugation of ubiquitin-like proteins is an antiviral strategy conserved across the tree of life.

ABSTRACT:
We have investigated the influence of the deformation temperature from 25 ◦ C (RT) to -196 ◦ C on the dislocation structures associated with strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C (wt.%) low-density steel by electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and bright-field transmitted forescattered electron imaging ((BF) t-FSEI) techniques. The characteristics of the dislocation structures were evaluated on the main texture components, i.e. <111>//tensile axis, <112>//tensile axis, and <001>//tensile axis directions. The inhomogeneous character of the plastic behavior is promoted upon cryogenic deformation due to the formation of dislocation structures associated with strain localization, namely microbands (MBs) and deformation bands (DBs). ECCI analysis of the dislocation structure reveals that the deformation temperature has a strong influence on the thermal-assisted dislocation processes controlling the dislocation configurations and MB formation mechanisms. The MB nucleation mechanism evolves from a crossslip-assisted mechanism at RT deformation conditions to a slip band-assisted mechanism at cryogenic deformation temperatures. This effect has a profound effect on the grain orientation dependence of the MB structure but not on its crystallographic alignment. On the other hand, cryogenic deformation temperatures (-196 ◦ C) enhance the material’s mechanical strength and ductility due to the activation of deformation twinning, which is associated with the reduction of the stacking fault energy. We find that MBs have a small contribution to strain-hardening and ductility due to the small mechanical resistance of these dislocation structures against the advance of deformation twins and dense dislocation layers, and the comparatively small plastic strain accommodated by them, respectively. These findings provide new insights into the microband-induced plasticity (MBIP) effect.

ABSTRACT:
In order to adhere to strict emissions standards, it is necessary to reduce diesel particulate emissions under real driving conditions. This can be achieved by reducing the production of soot particles and optimising the combustion process within the combustion chamber. This investigation examines the impact of engine operating conditions (transient and steady-state) on the characterisation of the soot particles. Soot samples from a common rail direct injection (CRDI), turbocharged six-cylinder diesel engine without any aftertreatment devices were collected on TEM grids. This investigation utilised both pure diesel and diesel-dioctyl phthalate (DOP) blends (D90DOP10 and D80DOP20). To correlate the soot characterisation results, diesel particulate emissions were also measured using a fast particle analyser (DMS500). The results indicate that emissions from transient cycles are higher in comparison to steady-state engine operation. Smaller primary particle diameter with a compact structure were observed for transient cycles when compared to steady-state operating conditions. Parameters such as number of primary particles within a single aggregate, radius of gyration, and soot aggregate area were also studied. Nanostructure analysis reveals that the soot particles from transient cycles could have lower oxidation reactivity and longer fringes with less curvature and interplanar spacing.

ABSTRACT:
Indium-based solder alloys are considered candidates for the next generation of low-temperature solder materials, especially for superconducting joints because of the properties of the β-In₃Sn phase. The temperature-dependent phase transformation and thermal expansion behaviour of two different solder compositions including In-35Sn (in wt.%) and In-25.6Sn have been charac- terised using an in situ synchrotron powder X-ray diffraction method. The c- axis of the β-In₃Sn unit cell in the In-35Sn alloy exhibited a complex rela- tionship with increasing temperature compared to the positive increasing trend in In-25.6Sn due to the temperature-dependent solubility of Sn in β- In₃Sn and change in the volume fraction of phases commencing at 80°C. In situ heating scanning electron microscopy recorded a real-time melting-so- lidification microstructure variation and phase transition during annealing at 90°C that was further analysed using energy dispersive X-ray spectroscopy. The observations are discussed with respect to the lattice parameters of the γ- InSn₄ and β-In₃Sn phases and the proportions and composition of both phases present within the alloys.

ABSTRACT:
Reliable and consistent preparation of atom probe tomography (APT) specimens from aqueous and hydrated biological specimens remains a significant challenge. One particularly difficult process step is the use of a focused ion beam (FIB) instrument for preparing the required needle-shaped specimen, typically involving a “lift-out” procedure of a small sample of material. Here, two alternative substrate designs are introduced that enable using FIB only for sharpening, along with example APT datasets. The first design is a laser-cut FIB-style half-grid close to those used for transmission-electron microscopy, that can be used in a grid holder compatible with APT pucks. The second design is a larger, standalone self-supporting substrate called a “crown,” with several specimen positions that self-aligns in APT pucks, prepared by electrical discharge machining (EDM). Both designs are made nanoporous, to provide strength to the liquid-substrate interface, using chemical and vacuum dealloying. We select alpha brass a simple, widely available, lower-cost alternative to previously proposed substrates. We present the resulting designs, APT data, and provide suggestions to help drive wider community adoption.

ABSTRACT:
Columnar mesoporous silicon (PSi) with hydrophobic vs. hydrophilic chemistries was chosen as a model for the local (pore-by-pore) study of water-pore interactions. Tomographic reconstructions provided a 3D view of the ramified pore structure. An in situ study of PSi wetting was conducted for categorized pore diameters by environmental scanning TEM. An appropriate setting of the contrast allows for the normalization of the gray scale in the images as a function of relative humidity (RH). This allows constructing an isotherm for each single pore and a subsequent averaging provides an isotherm for each pore size range. The isotherms systematically point to an initial adsorption through the formation of water adlayers, followed by a capillary filling process at higher RH. The local isotherms correlate with (global) gravimetric determination of wetting. Our results point at the validation of a technique for the study of aging and stability of single-pore nanoscale devices.

ABSTRACT:
Transition meta! oxides-based catalytic layers often present a complex 30 porous architecture affecting the evaluation of their intrinsic electrocatalytic activity. In this work the oxygen evolution reaction activity of coreshell Fe3O4@CoFe2O4 nanoparticles combining a conductive magnetite core and a catalytically active cobalt ferrite shell was studied at different loading and thickness of the catalytic layer. lt was observed that their apparent activity is decreasing and that the Tafel slopes are becoming convex when the loading increases. The activity decay could be attributed to the significant resistance to charge transport in the thick porous catalyst layer. This resistance could be estimated by fitting the electrochemical impedance spectra using the transmission line model. The influence of the layer thickness on the experimental current-potential curves and on their Tafel slopes could be simulated using a simple model based on the Telegrapher·s equations. lt is concluded that in order to measure accurately the activity and Tafel slopes of an electrocatalyst, thin layers must be used, notably for catalyst layers that are not highly conductive.

ABSTRACT:
Mined sub-aerially stored kimberlite provided a natural laboratory in which to examine the potential for carbon sequestration in ultramafic materials. A 15 cm hand sample of ~50-year-old ‘cemented” coarse residue deposit (CRD) collected from a cemented surface layer in the Cullinan Diamond Mine tailings in Gauteng, South Africa, petrographic sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron – energy dispersive spectroscopy demonstrated that weathering produced extensive, secondary Ca/Mg carbonates demonstrated the encouraging effects of weathering on mineral carbonation of kimberlite. The examination of that acted as an inter-granular cement, increasing the competency of the CRD, i.e., producing a hand sample.
Nearly every grain in the sample, including primary, un-weathered angular carbonate clasts were coated in secondary, μm- to mm-scale carbonate layers, which are interpreted as secondary materials. DNA analysis of an biome consistent with soils, metal cycling and hydrocarbon degradation that was found within the secondary internal, aseptic sample of secondary carbonate revealed that the weathered kimberlite hosts adiverse microcarbonate, interpreted as a biomateral. The formation of secondary carbonate demonstrates that ‘waste kimberlite’ from diamond mining can serve as a resource for carbon sequestration.

ABSTRACT:
This work analyzes the influence of several microscope settings, namely, sample-forescattered electron detector (FSD) distance, and tilting conditions on the characteristics of the dislocation contrast imaged in transmission forescattered electron imaging (t-FSEI). The dislocation contrast behaviors of characteristic dislocation configurations of two Fe-based alloys, namely an α’- martensitic (body-centered cubic, bcc) Fe-33Ni alloy (wt.%), and an austenitic (face-centered cubic, fcc) Fe-30Mn-6.5Al-0.3C alloy (wt.%) were investigated on thin foil samples by using different on-axis transmission Kikuchi diffraction (TKD) configurations, namely t-FSEI, brightfield (BF) t-FSEI and electron channeling contrast imaging (ECCI). The set-ups use transmission Kikuchi electron patterns to orient the crystal into controlled diffraction conditions. Imaging parameters such as dislocation contrast intensity and information depth are analyzed and compared to those obtained in the ECCI mode under the same microscope conditions. These effects are associated with the attenuation of Bragg scattering by high-angle scattering processes and the electron channeling mechanism, respectively. The experimental analysis sets the microscope settings for optimum dislocation imaging in t-FSEI.

ABSTRACT:
The efficient energy use in multiple sectors of modern industry is partly based on the efficient use of high-strength, high-performance alloys that retain remarkable mechanical properties at elevated and high temperatures. High-entropy alloys (HEAs) represent the most recent class of these materials with a high potential for high-temperature high-strength applications. Aside from their chemical composition and microstructure-property relationship, limited information on the effect of heat treatment as a decisive factor for alloy design is available in the literature. This work intends to contribute to this research topic by investigating the effect of heat treatment on the microstructure and mechanical performance of an Al4.4Co26Cr19Fe18Ni27Ti5.6 HEA. The solution annealed state is compared to aged states obtained at different heat treatment times at 750 C. The temporal evolution of the matrix and the ’-precipitates are analyzed in terms of chemical composition, crystallography, size, shape, and volume fraction by means of scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The yield strength evolution and strength contributions are calculated by classical state-of-the-art models as well as by ab-initio-based calculations of the critical resolved shear stress. The findings indicate promising mechanical properties of the investigated alloy and provide insight not only into possible strengthening mechanisms but also into the evolution of main phases during the heat treatment.

ABSTRACT:
Fatigue crack growth (FCG) tests were conducted on a medium-Mn steel annealed at two intercritical annealing temperatures, resulting in different austenite (!) to ferrite (“) phase fractions and different ! (meta-)stabilities. Novel in-situ hydrogen plasma charging was combined with in-situ cyclic loading in an environmental scanning electron microscope (ESEM). The in-situ hydrogen plasma charging increased the fatigue crack growth rate (FCGR) by up to two times in comparison with the reference tests in vacuum. Fractographic investigations showed a brittle-like crack growth or boundary cracking manner in the hydrogen environment while a ductile transgranular manner in vacuum. For both materials, the plastic deformation zone showed a reduced size along the hydrogen-influenced fracture path in comparison with that in vacuum. The difference in the hydrogen-assisted FCG of the medium-Mn steel with different microstructures was explained in terms of phase fraction, phase stability, yielding strength and hydrogen distribution. This refined study can help to understand the FCG mechanism without or with hydrogen under in-situ hydrogen charging conditions and can provide some insights from the applications point of view.

ABSTRACT:
Fatigue crack growth (FCG) test was done on a pre-cracked single-edge notched tensile (SENT) specimen with oligocrystalline ferritic structure. Innovative in-situ hydrogen (H)- charging by plasma inside an environmental scanning electron microscope (ESEM) was adopted to directly observe the H in!uence on the FCG behavior of this material. Diverse in-situ and post-mortem characterization methods including secondary electron imaging, backscatter electron imaging, electron backscatter diffraction (EBSD) and scanning probe microscopy (SPM) were used to investigate the material’s behavior. It was observed that the crack growth rate was enhanced by about one magnitude when H was charged, in comparison with the reference test in vacuum (Vac). The FCG procedure was concluded as strongly associated with the plasticity evolution in the vicinity of the crack-tip. A simple model based on the restricted plasticity was proposed for the H-enhanced FCG behavior. A peculiar frequency dependency of the H-enhanced FCG behavior was observed at low loading frequencies (0.015 Hze0.15 Hz): under the same in-situ H-charging condition, a lower frequency gave a slower crack growth rate and vice versa. This behavior was explained by the thermally activated dislocation motion correlated with the plasticity shielding effect during crack growth.

ABSTRACT:
It is demonstrated that UV (LED at 365 nm) irradiation with subsequent heating (90–110 C) of the polystyrene matrix containing a soluble Au(I) compound ((Ph3P)Au(n-Bu)) results in the growth of gold nanoparticles within the sample bulk, as confirmed by UV-vis spectroscopy and TEM electron microscopy. Pure heating of the samples without previous UV irradiation does not provide gold nanoparticles, thereby facilitating optical image printing. Comparing the nanoparticles’ growth kinetics in samples with different precursor content suggests the nanoparticle growth mechanism through Au(I) autocatalytic reduction at the surface of a gold nanoparticle. Within the polymer matrix, this mechanism is suggested for the first time.

 
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ABSTRACT:
The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. Havre pumices are predominantly white or grey, however pink pumice is common in the raft. In subaerial explosive eruptions, pink pumice is understood to result from high-temperature atmospheric iron-oxidation. The presence of pink pumice questions the effusive eruption model for the Havre raft. Here we report results from X-ray Absorption Near Edge Structure spectroscopy, magnetic mea- surements, TEM imaging and glass chemistry that collectively show the colour results from increasing amounts of magnetite nanolites in the raft pumice glass oxidizing to hematite. This suggests a short-lived but powerful explosive eruption phase penetrated the water column allowing hot pyroclasts to oxidise in air. Our results therefore challenge the known depth limits for explosive eruptions in the marine realm and suggest pink pumice can be an indi- cator of magnetite nanolite-driven explosive eruptions.

ABSTRACT:
Hydrogen embrittlement can cause a dramatic deterioration of the mechanical properties of high-strength metallic materials. Despite decades of experimental and modelling studies, the exact underlying mechanisms behind hydrogen embrittlement remain elusive. To unlock understanding of the mechanism and thereby help mitigate the influence of hydrogen and the associated embrittlement, it is essential to examine the interactions of hydrogen with structural defects such as grain boundaries, dislocations and stacking faults. Atom probe tomography (APT) can, in principle, analyse hydrogen located specifically at such microstructural features but faces strong challenges when it comes to charging specimens with hydrogen or deuterium. Here, we describe three different workflows enabling hydrogen/deuterium charging of site-specific APT specimens: namely cathodic, plasma and gas charging. All the experiments in the current study have been performed on a model twinning induced plasticity steel alloy. We discuss in detail the caveats of the different approaches in order to help future research efforts and facilitate further studies of hydrogen in metals. Our study demonstrates successful cathodic and gas charging, with the latter being more promising for the analysis of the high-strength steels at the core of our work.

ABSTRACT:
Mined sub-aerially stored kimberlite provided a natural laboratory in which to examine the potential for carbon sequestration in ultramafic materials. A 15 cm hand sample of ~50-year-old ‘cemented’ coarse residue deposit (CRD) collected from a cemented surface layer in the Cullinan Diamond Mine tailings in Gauteng, South Africa, demonstrated the encouraging effects of weathering on mineral carbonation of kimberlite. The examination of petrographic sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron – energy dispersive spectroscopy demonstrated that weathering produced extensive, secondary Ca/Mg carbonates that acted as an inter-granular cement, increasing the competency of the CRD, i.e., producing a hand sample. Nearly every grain in the sample, including primary, un-weathered angular carbonate clasts were coated in secondary, μm- to mm-scale carbonate layers, which are interpreted as secondary materials. DNA analysis of an internal, aseptic sample of secondary carbonate revealed that the weathered kimberlite hosts a diverse micro- biome consistent with soils, metal cycling and hydrocarbon degradation that was found within the secondary carbonate, interpreted as a biomaterial. The formation of secondary carbonate demonstrates that ‘waste kimberlite’ from diamond mining can serve as a resource for carbon sequestration.

ABSTRACT:
Microbiological weathering of coarse residue deposit (CRD) kimberlite produced by the Venetia Diamond Mine, Limpopo, South Africa enhanced mineral carbonation relative to untreated material. Cultures of photosynthetically enriched biolm produced maximal carbonation conditions when mixed with kimberlite and incubated under near surface conditions. Interestingly, mineral carbonation also occurred in the dark, under water-saturated conditions. The examination of mineralized biolms in ca. 150 μm- thick-sections using light microscopy, X-ray uorescence microscopy (XFM) and backscatter electron – scanning election microscopy-energy dispersive spectroscopy demonstrated that microbiological weathering aided in producing secondary Ca/Mg carbonates on silicate grain boundaries. Calcium/magnesium sulphate(s) precipitated under vadose conditions demonstrating that evaporites formed upon drying. In this system, mineral carbonation was only observed in regions possessing bacteria, preserved within carbonate as cemented microcolonies. 16S rDNA molecular diversity of bacteria in kimberlite and in natural biolms growing on kimberlite were dominated by Proteobacteria that are active in N, P and S cycling. Photosynthetic enrichment cultures provided with N & P (nutrients) to enhance growth, possessed increased diversity of bacteria, with Proteobacteria re-establishing themselves as the dominant bacterial lineage when incubated under dark, vadose conditions consistent with natural kimberlite. Overall, 16S rDNA analyses revealed that weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation. Enhanced weathering and carbonate-cemented microcolonies demonstrate that microorganisms are key to mineral carbonation of kimberlite.

ABSTRACT:
Acinetobacter baumannii causes high mortality in ventilator-associated pneumonia patients, and antibiotic treatment is compromised by multidrug-resistant strains resistant to b-lactams, carbapenems, cephalosporins, polymyxins, and tetracy- clines. Among COVID-19 patients receiving ventilator support, a multidrug-resistant A. baumannii secondary infection is associated with a 2-fold increase in mortality. Here, we investigated the use of the 8-hydroxyquinoline ionophore PBT2 to break the resist- ance of A. baumannii to tetracycline class antibiotics. In vitro, the combination of PBT2 and zinc with either tetracycline, doxycycline, or tigecycline was shown to be bactericidal against multidrug-resistant A. baumannii, and any resistance that did arise imposed a !tness cost. PBT2 and zinc disrupted metal ion homeostasis in A. baumannii, increasing cellular zinc and copper while decreasing magnesium accumulation. Using a murine model of pulmonary infection, treatment with PBT2 in combination with tetracycline or tigecycline proved ef!cacious against multi- drug-resistant A. baumannii. These !ndings suggest that PBT2 may !nd utility as a resistance breaker to rescue the ef!cacy of tetracycline-class antibiotics com- monly employed to treat multidrug-resistant A. baumannii infections.

ABSTRACT:
Gram-positive bacteria do not produce lipopolysaccharide as a cell wall component. As such, the polymyxin class of antibiotics, which exert bactericidal activity against Gram-negative pathogens, are ineffective against Gram-positive bacteria. The safe-for-human-use hydroxyquinoline analog ionophore PBT2 has been previously shown to break polymyxin resistance in Gram-negative bacteria, independent of the lipopolysaccharide modification pathways that confer polymyxin re- sistance. Here, in combination with zinc, PBT2 was shown to break intrinsic polymyxin resistance in Streptococcus pyogenes (Group A Streptococcus; GAS), Staphylococcus aureus (including methicillin- resistant S. aureus), and vancomycin-resistant Enterococcus faecium. Using the globally disseminated M1T1 GAS strain 5448 as a proof of principle model, colistin in the presence of PBT2 + zinc was shown to be bactericidal in activity. Any resistance that did arise imposed a substantial fitness cost. PBT2 + zinc dysregulated GAS metal ion homeostasis, notably decreasing the cellular manganese content. Using a murine model of wound infection, PBT2 in combination with zinc and colistin proved an efficacious treatment against streptococcal skin infection. These findings provide a founda- tion from which to investigate the utility of PBT2 and next-generation polymyxin antibiotics for the treatment of Gram-positive bacterial infections.

ABSTRACT:
Electron microprobe-based quantitative compositional measurement of first-row transition metals using their La X-ray lines is hampered by, among other effects, self-absorption. This effect, which occurs when a broad X-ray line is located close to a broad absorption edge, is not accounted for by matrix corrections. To assess the error due to neglecting self-absorption, we calculate the La X-ray intensity emitted from metallic Fe, Ni, Cu, and n targets, assuming a Lorentzian profile for the X-ray line and taking into account the energy dependence of the mass absorption coefficient near the absorption edge. We find that calculated X-ray intensities depart increasingly, for increasing electron beam energy, from those obtained assuming a narrow X-ray line and a single fixed absorption coefficient (conventional approach), with a maximum deviation of ~15% for Ni and of ~10% for Fe. In contrast, X-ray intensities calculated for metallic n and Cu do not differ significantly from those obtained using the conventional approach. The implications of these results for the analysis of transition-metal compounds by electron probe microanalysis as well as strategies to account for self-absorption effects are discussed.

ABSTRACT:
The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. Havre pumices are predominantly white or grey, however pink pumice is common in the raft. In subaerial explosive eruptions, pink pumice is understood to result from high-temperature atmospheric iron-oxidation. The presence of pink pumice questions the effusive eruption model for the Havre raft. Here we report results from X-ray Absorption Near Edge Structure spectroscopy, magnetic measurements, TEM imaging and glass chemistry that collectively show the colour results from increasing amounts of magnetite nanolites in the raft pumice glass oxidizing to hematite. This suggests a short-lived but powerful explosive eruption phase penetrated the water column allowing hot pyroclasts to oxidise in air. Our results therefore challenge the known depth limits for explosive eruptions in the marine realm and suggest pink pumice can be an indicator of magnetite nanolite-driven explosive eruptions.

ABSTRACT:
Ultrathin metallic films are important functional materials for optical and microelectronic devices. Dedicated characterization with high spatial resolution and sufficient field of view is key to the understanding of the relation between microstructure and optical and electrical properties of such thin films. Here, we have applied on-axis transmission Kikuchi diffraction (TKD) and scanning precession electron diffraction (SPED) to study the microstructure of 10 nm thick polycrystalline gold films. The study compares the results obtained from the same specimen region by the two techniques and provides insights on the limits of each diffraction technique. We compare the physical spatial resolution of on-axis TKD and SPED and discuss challenges due to the larger probe size in scanning electron microscopy (SEM). Moreover, we present an improvement for the physical spatial resolution (PSR) of on-axis TKD through acquisition in immersion mode. We show how this method extends the capabilities of SEM-based microstructure characterization of ultrathin films and achieve PSR comparable to semi-automated SPED.

ABSTRACT:
Gram-positive bacteria do not produce lipopolysaccharide as a cell wall component. As such, the polymyxin class of antibiotics, which exert bactericidal activity against Gram-negative pathogens, are ineffective against Gram-positive bacteria. The safe-for-human-use hydroxyquinoline analog ionophore PBT2 has been previously shown to break polymyxin resistance in Gram-negative bacteria, independent of the lipopolysaccharide modification pathways that confer polymyxin resistance. Here, in combination with zinc, PBT2 was shown to break intrinsic polymyxin resistance in Streptococcus pyogenes (Group A Streptococcus; GAS), Staphylococcus aureus (including methicillin-resistant S. aureus), and vancomycin-resistant Enterococcus faecium. Using the globally disseminated M1T1 GAS strain 5448 as a proof of principle model, colistin in the presence of PBT2 + zinc was shown to be bactericidal in activity. Any resistance that did arise imposed a substantial fitness cost. PBT2 + zinc dysregulated GAS metal ion homeostasis, notably decreasing the cellular manganese content. Using a murine model of wound infection, PBT2 in combination with zinc and colistin proved an efficacious treatment against streptococcal skin infection. These findings provide a foundation from which to investigate the utility of PBT2 and next-generation polymyxin antibiotics for the treatment of Gram-positive bacterial infections.

ABSTRACT:
The extracellular matrix (ECM) is an essential component of the tumor microenvironment. It plays a critical role in regulating cell-cell and cell-matrix interactions. However, there is lack of systematic and comparative studies on different widely-used ECM mimicking hydrogels and their properties, making the selection of suitable hydrogels for mimicking different in vivo conditions quite random. This study systematically evaluates the biophysical attributes of three widely used natural hydrogels (Matrigel, collagen gel and agarose gel) including complex modulus, loss tangent, diffusive permeability and pore size. A new and facile method was developed combining Critical Point Drying, Scanning Electron Microscopy imaging and a MATLAB image processing program (CSM method) for the characterization of hydrogel microstructures. This CSM method allows accurate measurement of the hydrogel pore size down to nanometer resolution. Furthermore, a microfluidic device was implemented to measure the hydrogel permeability (Pd) as a function of particle size and gel concentration. Among the three gels, collagen gel has the lowest complex modulus, medium pore size, and the highest loss tangent. Agarose gel exhibits the highest complex modulus, the lowest loss tangent and the smallest pore size. Collagen gel and Matrigel produced complex moduli close to that estimated for cancer ECM. The Pd of these hydrogels decreases significantly with the increase of particle size. By assessing different hydrogels’ biophysical characteristics, this study provides valuable insights for tailoring their properties for various three-dimensional cancer models.

ABSTRACT:
The nasopharynx and the skin are the major oxygen-rich anatomical sites for colonization by the human pathogen Streptococcus pyogenes (group A Streptococcus [GAS]). To establish infection, GAS must survive oxidative stress generated during aerobic metabo-lism and the release of reactive oxygen species (ROS) by host innate immune cells. Glutathione is the major host antioxidant molecule, while GAS is glutathione auxotrophic. Here, we report the molecular characterization of the ABC transporter substrate binding protein GshT in the GAS glutathione salvage pathway. We demonstrate that glutathione uptake is critical for aerobic growth of GAS and that impaired import of glutathione indu-ces oxidative stress that triggers enhanced production of the reducing equivalent NADPH. Our results highlight the interrelationship between glutathione assimilation, carbohydrate metabolism, virulence factor production, and innate immune evasion. Together, these find-ings suggest an adaptive strategy employed by extracellular bacterial pathogens to exploit host glutathione stores for their own benefit.

ABSTRACT:
Streptococcus pneumoniae is the primary cause of community-acquired bacterial pneumonia with rates of penicillin and multidrug-resistance exceeding 80% and 40%, respectively. The innate immune response gen­erates a variety of antimicrobial agents to control infection, including zinc stress. Here, we characterize the impact of zinc intoxication on S. pneumoniae, observing disruptions in central carbon metabolism, lipid biogenesis, and peptidoglycan biosynthesis. Characterization of the pivotal peptidoglycan biosynthetic enzyme GlmU indicates a sensitivity to zinc inhibition. Disruption of the sole zinc efflux pathway, czcD, renders S. pneumoniae highly susceptible to ß-lactam antibiotics. To dysregulate zinc homeostasis in the wild-type strain, we investigated the safe-for-human-use ionophore 5,7-dichloro-2-[(dimethylamino) methyl]quinolin-8-ol (PBT2). PBT2 rendered wild-type S. pneumoniae strains sensitive to a range of antibi­otics. Using an invasive ampicillin-resistant strain, we demonstrate in a murine pneumonia infection model the efficacy of PBT2 + ampicillin treatment. These findings present a therapeutic modality to break antibiotic resistance in multidrug-resistant S. pneumoniae.

ABSTRACT:
The influence of helium co-injection at rates from 0 to 4 appm He/dpa on swelling in ferritic-martensitic alloys T91 and HT9 was explored. Irradiations with 5.0 MeV Fe⁺⁺ ions and degraded He⁺⁺ ions were performed at 445°C up to damage levels of 150 dpa and helium co-injection rates of 0, 0.02, 0.2 and 4 appm He/dpa in T91, and at 460°C to a damage level of 188 dpa and helium co-injection rates of 0, 0.06 and 4 appm He/dpa in HT9. Helium was observed to enhance cavity nucleation at low damage levels, resulting in the maximum swelling at the highest helium co-injection rate. As the damage level was increased, the helium content at which swelling was maximized shifted to lower helium concentrations, ultimately resulting in the highest swelling occurring with zero helium by 150 dpa. This behavior was due to the helium-stabilized bubble microstructure that increased the cavity sink strength and reduced both cavity growth rate and swelling relative to the helium-free condition.

ABSTRACT:
The magnetron sputtered tantalum diboride (TaB_y) coatings from stoichiometric TaB₂ target are often reported to be deposited in broad B/Ta interval with diverse structure and mechanical properties. In this article, the effect of Ar neutrals reflected from TaB₂ target on the B/Ta ratio is examined. Two targets with different thickness are used to influence the current-voltage characteristic of the discharge and the energy of reflected Ar neutrals. In addition, external magnetic field from Helmholtz coils is applied to influence the plasma density in the substrate region. It is demonstrated that the reflected Ar neutrals have a significant effect on B/Ta ratio reduction from 1.9 to 1.4. While decreasing the B/Ta ratio, preferred TaB_y crystal orientation changes from (0001) to (101̅1). Intense Ar bombardment results in loss of crystallinity exemplified by diffraction maxima broadening. The variation of B/Ta ratio is accompanied by change of hardness and Young’s modulus in range from 48 GPa to 32 GPa and from 532 GPa to 390 GPa, respectively. The coatings with B/Ta ratio < 1.6 show material pile-up around cube-corner indents, an indication for improved ductility.

ABSTRACT:
Bio-concrete is known for its self-healing capacity although the corrosion resistance was not investigated previously. This study presents an innovative bio-concrete by mixing anaerobic granular sludge into concrete to mitigate sewer corrosion. The control concrete and bio-concrete (with granular sludge at 1% and 2% of the cement weight) were partially submerged in a corrosion chamber for 6 months, simulating the tidal-region corrosion in sewers. The corrosion rates of 1% and 2% bio-concrete were about 17.2% and 42.8% less than that of the control concrete, together with 14.6% and 35.0% less sulfide uptake rates, 15.3% and 55.6% less sulfate concentrations, and higher surface pH (up to 1.8 units). Gypsum and ettringite were major corrosion products but in smaller sizes on bio-concrete than that of control concrete. The total relative abundance of corrosion-causing microorganisms, i.e. sulfide-oxidizing bacteria, was significantly reduced on bio-concrete, while more sulfate-reducing bacteria (SRB) was detected. The corrosion-resistance of bio-concrete was mainly attributed to activities of SRB derived from the granular sludge, which supported the sulfur cycle between the aerobic and anaerobic corrosion sub-layers. This significantly reduced the net production of biogenic sulfuric acid and thus corrosion. The results suggested that the novel granular sludge-based bio-concrete provides a highly potential solution to reduce sewer corrosion.

ABSTRACT:
Meropenem (MER) is one of the last resort antibiotics used to treat resistant bacterial infections. However, the clinical effectiveness of MER is hindered due to chemical instability in aqueous solution and gastric pH, and short plasma half-life. Herein, a novel multi-material delivery system based on γ-cyclodextrin (γ-CD) and poly lactic-co-glycolic acid (PLGA) is demonstrated to overcome these challenges. MER showed a saturated solubility of 14 mg/100 mL in liquid CO2 and later it was loaded into γ-CD to form the inclusion complex using the liquid CO2 method. The γ-CD and MER inclusion complex (MER-γ-CD) was encapsulated into PLGA by the well-established double emulsion solvent evaporation method. The formation of the inclusion complex was confirmed using FTIR, XRD, DSC, SEM, and 1H NMR and docking study. Further, MER-γ-CD loaded PLGA nanoparticles (MER-γ-CD NPs) were characterized by SEM, DLS, and FTIR. The drug loading and entrapment efficiency for MER-γ-CD were 21.9 and 92. 2% w/w, respectively. However, drug loading and entrapment efficiency of MER-γ-CD NPs was significantly lower at up to 3.6 and 42.1% w/w, respectively. In vitro release study showed that 23.6 and 27.4% of active (non-degraded drug) and total drug (both degraded and non-degraded drug) were released from MER-γ-CD NPs in 8 h, respectively. The apparent permeability coefficient (Papp) (A to B) for MER, MER-γ-CD, and MER-γ-CD NPs were 2.63 × 10-6 cm/s, 2.81 × 10-6 cm/s, and 2.92 × 10-6 cm/s, respectively. For secretory transport, the Papp (B to A) were 1.47 × 10-6 cm/s, 1.53 × 10-6 cm/s, and 1.58 × 10-6 cm/s for MER, MER-γ-CD and MER-γ-CD NPs, respectively. Finally, the MER-γ-CD inclusion complex and MER-γ-CD NPs retained MER’s antibacterial activities against Staphylococcus aureus and Pseudomonas aeruginosa. Overall, this work demonstrates the significance of MER-γ-CD NPs to protect MER from gastric pH with controlled drug release, while retaining MER’s antibacterial activity.

ABSTRACT:
Meropenem (MER) is an effective broad-spectrum antibiotic currently only available in the parenteral form requiring frequent drug preparation and administration due to its extremely poor stability. The unavailability of oral Meropenem is primarily due to its ultrapoor handling and processing stability, hydrophilic nature that inhibits the passive diffusion across the gastrointestinal (GI) epithelium, degradation in the harsh gastric environment, and GI expulsion through enterocyte efflux glycoproteins. In this regard, we have developed an oral drug delivery system that confines MER into mesoporous silica nanoparticles (MSNs i.e, MCM-41 ∼141 nm) using a novel liquid carbon dioxide (CO2) method. MER was efficiently encapsulated within pristine, phosphonate (negatively charged MSN), and amine (positively charged MSN) modified MSNs with loading capacity ranging between 25 wt % and 31 wt %. Next, the MER-MCM-NH2 particles were electrostatically coated with Eudragit S100 enteric polymer that protected MER against gastric pH (pH 1.9) and enabled site-specific delivery in the small intestine (pH 6.8). Cellular uptake results in RAW 264.7 macrophage, Caco-2, and LS174T cells confirming the efficient cellular uptake of nanoparticles in all three cell lines. More importantly, the bidirectional transport (absorptive and secretory) of MER across Caco-2 monolayer was significantly improved for both MSN-based formulations, particularly MSNs coated with a polymer (Eud-MER-MCM-NH2) where permeability was significantly enhanced (∼2.4-fold) for absorptive transport and significantly reduced (∼1.8-fold) for secretory transport. Finally, in vitro antibacterial activity [minimum inhibitory concentration (MIC)] and time-kill assay against S. aureus and P. aeruginosa showed that drug-loaded nanoparticles were able to retain antibacterial activity comparable to that of free MER in a solution at equivalent dose. Thus, Eudragit-coated silica nanoparticles could offer a promising and novel solution for oral delivery of Meropenem and other such drugs.

ABSTRACT:
Bio-based plastics, produced from renewable biomass sources, may contribute to lowering greenhouse gases and the demand for fossil resources. However, their environmental fate is not well understood. Here, we compared the impacts of industrially produced granules (G) and micro-debris (MD) from three pristine bio-based plastics: high-density polyethylene (HDPE), polylactic acid (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) on natural bacterial communities in seawater and freshwater using metagenomics. After one month, we found a dissimilarity between the microbial communities forming a biofilm on the plastics and planktonic bacteria. Further, different bacterial groups became dominant on different bio-based plastics, i.e. Burkholderiaceae, Solimonadaceae, Oleiphilaceae, and Sneathiellaceae on HDPE and Alteromonadaceae on PLA and Rhodobacteraceae on PHBV in seawater, and Beijerinckiaceae and Chitinophagaceae on HDPE, Microtrichaceae on PLA and Caulobacteraceae and Sphingomonadaceae on PHBV in freshwater. Variovorax, Albimonas and Sphingomonas genera were recorded on bio-based plastics in both seawater and freshwater. This study describes how different bio-based plastic materials and granule sizes influence the development of natural bacterial communities.

ABSTRACT:
In this study, a single-stage up-flow fixed-bed sulfidogenic bioreactor was operated for 288 days (six stages), treating mine-impacted water at different concentrations of nickel (Ni), cobalt (Co) and other associated metals. The effect of metals on the sulfate reducing activity, metal recovery, extracellular proteins and microbial diversity was evaluated. The bioreactor configuration showed a positive synergistic effect on both sulfate reducing activity and metals recovery, which could treat up to 200 mg/L Ni. Over 99% of Ni and Co, as well as over 91% of the other metals in the influent, precipitated and settled in the bioreactor regardless of the initial metal concentration. The scanning electron microscopy (SEM) analysis of the precipitates showed the presence of extracellular polymeric substances (EPS), which may have helped to agglomerate the metal sulfide precipitates increasing their ‘particle size’ from 0.1 to 0.5 μm to 10–100 μm. Different extracellular proteins associated to these EPS increased in abundance upon variations of the bioreactor operation. These included proteins involved in enzymatic reactions and metal binding, such as periplasmic [NiFeSe] hydrogenase, standing out when Ni and Co was added. The biofilm characterization showed the dominance of metal-tolerant SRB genera (e.g., Desulfomicrobium spp. and Desulfovibrio spp.), but also of other non-SRB, demonstrating that a higher microbial diversity may help the biofilm endure higher metal concentrations.

ABSTRACT:
The construction of a solar sail from commercially available metallized film presents several challenges. The solar sail membrane is made by seaming together precut lengths of ultrathin metallized polymer film into the required geometry. This assembled sail membrane is then folded into a small stowage volume prior to launch. The sail membranes must have additional features for connecting to rigid structural elements (e.g., sail booms) and must be electrically grounded to the spacecraft bus to prevent charge build up. Space durability of the material and mechanical interfaces of the sail membrane assemblies will be critical for the success of any solar sail mission. In this study, interfaces of polymer/metal joints in a representative solar sail membrane assembly were tested to ensure that the adhesive interfaces and the fastening grommets could withstand the temperature range and expected loads required for mission success. Various adhesion methods, such as surface treatment, commercial adhesives, and fastening systems, were experimentally tested in order to determine the most suitable method of construction.

ABSTRACT:
The exploitation of facile preparation methods and novel applications of entropy alloys has gained ever-increasing attention in recent years. In this paper, homogeneous FeCoNiCu medium entropy alloys (MEAs) with a face-centered cubic (FCC) structure are prepared by the electrochemical reduction of oxides in molten Na₂CO₃-K₂CO₃ using a low-cost Ni10Cu11Fe oxygen-evolution inert anode. The current efficiency reaches 85.3% with a low energy consumption of 2.9 kWh/kg-MEA. At the cathode, Ni acts as a solvent to dissolve other elements and facilitate the formation of the FCC phase, and the co-reduction process enhances the element diffusion rate thereby ensuring the homogeneity of the electrolytic MEAs. In addition, the electrolytic MEAs are pressed into pellet electrodes with an in situformed oxides layer to catalyze oxygen evolution reactions (OER) in 1.0 M KOH solution. The electrocatalytic activity of the electrolytic MEAs outperforms the commercial IrO₂/Ta₂O₅-Ti electrode, i.e., the overpotential of the electrode is 439 mV at 50 mA/cm² and the electrode lasts for 10 h without any degradation. Therefore, this paper provides a facile approach to preparing homogeneous MEAs at below 1173 K using oxides feedstock, to accurately controlling compositions and structures of MEAs, and thereby to tailoring functionalities of MEAs.

ABSTRACT:
It is well known that carbon present in scanning electron microscopes (SEM), Focused ion beam (FIB) systems and FIB-SEMs, causes imaging artefacts and influences the quality of TEM lamellae or structures fabricated in FIB-SEMs. The severity of such effects depends not only on the quantity of carbon present but also on its bonding state. Despite this, the presence of carbon and its bonding state is not regularly monitored in FIB-SEMs. Here we demonstrated that Secondary Electron Hyperspectral Imaging (SEHI) can be implemented in different FIB-SEMs (ThermoFisher Helios G4-CXe PFIB and Helios Nanolab G3 UC) and used to observe carbon built up/removal and bonding changes resulting from electron/ion beam exposure. As well as the ability to monitor, this study also showed the capability of Plasma FIB Xe exposure to remove carbon contamination from the surface of a Ti6246 alloy without the requirement of chemical surface treatments.

ABSTRACT:
Vacuum chambers are frequently used in high-energy, high-peak-power laser systems to prevent deleterious nonlinear effects, which can result from propagation in air. In the vacuum sections of the Allegra laser system at ELI-Beamlines, we observed degradation of several optical elements due to laser-induced contamination (LIC). This contamination is present on surfaces with laser intensity above 30 GW/cm 2 with wavelengths of 515, 800, and 1030 nm. It can lead to undesired absorption on diffraction gratings, mirrors, and crystals and ultimately to degradation of the laser beam profile. Because the Allegra laser is intended to be a high-uptime source for users, such progressive degradation is unacceptable for operation. Here, we evaluate three methods of removing LIC from optics in vacuum. One of them, the radio-frequency-generated plasma cleaning, appears to be a suitable solution fromtheperspective of operating a reliable, on-demand source for users.
 

J. Saujauddin, T. Niemi, T. Lundquist, B. Niu, M. Cable

ABSTRACT:
anoprobing has become indispensable for the characterization of FEOL processes and FinFET performance in early process development and HVM yield improvements [1- 3]. When the processes and transistor performance are fully characterized such as transistor level I-V curves (performance) and leakage (power efficiency), the risk to process development is greatly reduced, providing high impact to the HVM-product performances.

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Ronald Vane, Ewa Kosmowska and Michael Cable

ABSTRACT:
The Evactron remote plasma cleaner was introduced in 1999 for cleaning SEM chambers and stages with air flowing through a hollow cathode RF plasma that produces oxygen radicals for chemical etching. Since the initial introduction of Evactron plasma cleaners over 3500 units have been sold worldwide.

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Barbara Armbruster, Michael Cable, Ewa Kosmowska, Kim Larsen, Patrick Trimby and Ronald Vane

ABSTRACT:
Plasma cleaners have been recognized as a necessary accessory for rapidly and effectively eliminating hydrocarbon contamination from vacuum chambers and samples. Operating at turbopump pressures, the Evactron plasma radical source with a unique RF hollow cathode generates a low-temperature RF plasma to create oxygen radicals when air is the feed gas. The oxygen radicals combine with surface hydrocarbons to form gaseous phases which are removed by the pumping system. The benefits of plasma cleaning include faster pumpdown times, improved image quality of serial block-face SEM volumetric sets, prevention of hydrocarbon deposition during imaging and no damage to EDS detectors or x-ray windows due to oxygen radical generation.

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Michael Tkadletza, Alexandra Lechnera, Nina Schalka, Bernhard Sartoryc, Andreas Starkd, Norbert Schelle, Christian Saringer, Christian Mitterer, Christoph Czettl

ABSTRACT:
Recently, it was shown that annealing of nanolamellar CVD fcc-Ti 1-x Al x N at temperatures of 1000-1200 °C results in the formation of complex phase fields consisting of still intact nanolamellar face centered cubic (fcc) zones, side by side with non-lamellar fully decomposed and transformed fcc and wurtzite (w) zones. It can be assumed that the observed phase fields and their microstructure strongly correlate with their mechanical properties. Consequently, this work focuses on the investigation of the effects of spinodal decomposition and fcc →w phase transformation of a nanolamellar CVD fcc-Ti 0.2 Al 0.8 N coating on the corresponding global and local mechanical properties. The sequence of spinodal decomposition and fcc →w phase transformation of a compact coating sample was investigated by in situ high temperature synchrotron X-ray diffraction up to a maximum temperature of ~1250 °C. Conventional nanoindentation experiments on the surfaces of samples annealed between 900 to 1300 °C in vacuum were performed to illustrate the age hardening and overaging behavior. Finally, the influence of the observed phase fields on the local mechanical properties was investigated by correlative SEM/EBSD and nanomechanical mapping experiments on a cross-section of a coating annealed at 1050 °C. Maps of the lateral microstructure, phase composition, Young´s modulus and hardness of the coating were successfully obtained with a resolution of ≤ 100 nm. The lateral phase fields could be clearly identified and correlated with the observed mechanical properties. The results indicate that age hardening of nanolamellar CVD fcc-Ti 0.2 Al 0.8 N coatings occurs homogeneously, while overaging is associated to the fcc →w transformation and thus, locally confined.

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Viktor Šroba, Tomáš Fiantok, Martin Truchlý, Tomáš Roch, Miroslav Zahoran, Branislav Grančič, Peter Švec, Jr., Štefan Nagy, Vitalii Izai, Peter Kúš and Marián Mikula

ABSTRACT:
Tantalum diboride (TaB2 ) belonging to the ultrahigh temperature ceramics family is proving to be a promising material for hard protective films, thanks to its high thermal stability and excellent mechanical properties. However, growth of TaB 2 ± x films prepared using physical vapor deposition techniques is strongly affected by Ar neutrals reflected from a stoichiometric TaB 2 target due to a significant mass difference of heavy Ta and light B atoms leading to substantial changes in the final chemical composition and structure of films. In this work, TaB 2 ± x films are experimentally prepared using high target utilization sputtering. Stopping and range of ions in matter simulations are used to investigate the behavior of Ar neutrals during deposition processes. A wide range of analytical methods is used to completely characterize the chemical composition, structure, and mechanical properties of TaB 2 ± x films, and the explanation of the obtained results is supported by density functional theory calculations. TaB 2 ± x films grow in a broad compositional range from TaB 1.36 to TaB 3.84 depending on the kinetic energy of Ar neutrals. The structure of overstoichiometric TaB 2 + x films consists of 0001 preferentially oriented α-TaB 2 nanocolumns surrounded by a boron-tissue phase. In the case of highly understoichiometric TaB 2 − x films, the boron-tissue phase disappears and the structure consisting of 0001 and 10
11 oriented α-TaB 2 nanocolumns is formed. All TaB 2 ± x films exhibit excellent mechanical properties with high hardness, ranging from 27 to 43 GPa and relatively low values of Young’s modulus in the range of 304–488 GPa.

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Aiden A. Martin, Jorge Filevich, Marcus Straw, Steven Randolph, Aur´elien Botman, Igor Aharonovich and Milos Toth

ABSTRACT:
Ultra nano-crystalline diamond (UNCD) is increasingly being used in the fabrication of devices and coatings due to its excellent tribological properties, corrosion resistance and bio-compatibility. Here, we study its response to irradiation with kiloelectronvolt electrons as a controlled model for extreme ionizing environments. Real time Raman spectroscopy reveals that the radiation damage mechanism entails dehydrogenation of UNCD grain boundaries, and we show that the damage can be recovered by annealing at 883 K. Our results have significant practical implications for the implementation of UNCD in extreme environment applications, and indicate that the films can be used as radiation sensors.

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Alex M. Lord, Vincent Consonni, Thomas Cossuet, Fabrice Donatini and Steve P. Wilks

ABSTRACT:
Polarity-controlled growth of ZnO by chemical bath deposition provides a method for controlling the crystal orientation of vertical nanorod arrays.

The ability to define the morphology and structure of the nanorods is essential to maximizing the performance of optical and electrical devices such as piezoelectric nanogenerators; however, well-defined Schottky contacts to the polar facets of the structures have yet to be explored. In this work, we demonstrate a process to fabricate metal−semiconductor−metal device structures from vertical arrays with Au contacts on the uppermost polar facets of the nanorods and show that the Opolar nanorods (∼0.44 eV) have a greater effective barrier height than the Znpolar nanorods (∼0.37 eV). Oxygen plasma treatment is shown by cathodoluminescence spectroscopy to affect midgap defects associated with radiative emissions, which improves the Schottky contacts from weakly rectifying to strongly rectifying. Interestingly, the plasma treatment is shown to have a much greater effect in reducing the number of carriers in O-polar nanorods through quenching of the donor-type substitutional hydrogen on oxygen sites (HO ) when compared to the zinc-vacancy-related hydrogen defect complexes (VZn −nH) in Zn-polar nanorods that evolve to lowercoordinated complexes. The effect on H O in the O-polar nanorods coincides with a large reduction in the visible-range defects, producing a lower conductivity and creating the larger effective barrier heights. This combination can allow radiative losses and charge leakage to be controlled, enhancing devices such as dynamic photodetectors, strain sensors, and light-emitting diodes while showing that the O-polar nanorods can outperform Zn-polar nanorods in such applications.

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Alona Keren-Paz, Malena Cohen-Cymberknoh, Dror Kolodkin-Gal, Iris Karunker, Simon Dersch, Sharon G. Wolf, Tsviya Olender, Elena Kartvelishvily, Sergey Kapishnikov, Peninnah Green-Zelinger, Michal Shteinberg, Gideon Zamir, Assaf Gal, Peter Graumann, Eitan Kerem and Ilana Kolodkin-Gal

ABSTRACT:
Bacterial biofilms produce a robust internal mineral layer, composed of calcite, which strengthens the colony and protects the residing bacteria from antibiotics. In this work, we provide evidence that the assembly of a functional mineralized macro-structure begins with mineral precipitation within a defined cellular compartment in a differentiated subpopulation of cells. Transcriptomic analysis of a model organism, Bacillus subtilis, revealed that calcium was essential for activation of the biofilm state, and highlighted the role of cellular metal homeostasis and carbon metabolism in biomineralization. The molecular mechanisms promoting calcite formation were conserved in pathogenic Pseudomonas aeruginosa biofilms, resulting in formation of calcite crystals tightly associated with bacterial cells in sputum samples collected from cystic fibrosis patients. Biomineralization inhibitors targeting calcium uptake and carbonate accumulation significantly reduced the damage inflicted by P. aeruginosa biofilms to lung tissues. Therefore, better understanding of the conserved molecular mechanisms promoting biofilm calcification can path the way to the development of novel classes of antibiotics to combat otherwise untreatable biofilm infections.

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Yue Hui, Xin Yi, David Wibowo, Guangze Yang, Anton P. J. Middelberg, Huajian Gao, Chun-Xia Zhao

ABSTRACT:
The ability of cells to sense external mechanical cues is essential for their adaptation to the surrounding microenvironment. However, how nanoparticle mechanical properties affect cell-nanoparticle interactions remains largely unknown. Here, we synthesized a library of silica nanocapsules (SNCs) with a wide range of elasticity (Young’s modulus ranging from 560 kPa to 1.18 GPa), demonstrating the impact of SNC elasticity on SNC interactions with cells. Transmission electron microscopy revealed that the stiff SNCs remained spherical during cellular uptake. The soft SNCs, however, were deformed by forces originating from the specific ligand-receptor interaction and membrane wrapping, which reduced their cellular binding and endocytosis rate. This work demonstrates the crucial role of the elasticity of nanoparticles in modulating their macrophage uptake and receptor-mediated cancer cell uptake, which may shed light on the design of drug delivery vectors with higher efficiency.

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Ling Tana, Thomas Ray Jonesb, Jordan Poitrasb, Jianping Xiea, Xinxing Liua, Gordon Southamb

ABSTRACT:
Palladium nanoparticles (PdNPs) can catalyse a range of reductive chemical reactions transforming both organic and inorganic environmental pollutants. PdNPs that ranged from < 2 to 2–40 nm were synthesized using chemical methods, and bacterial biomass with/without chemical fixatives. PdNP formation was enhanced by adsorption of Pd(II) to bacterial biomass, followed by fixation with formate or glutaraldehyde. TEM-SAED analyses confirmed that the cell associated PdNPs were polycrystalline with a face-centered cubic structure. Chemically formed PdNPs possessed a higher Pd(0):Pd(II) ratio and produced structurally similar nanoparticles as the biotic systems. These PdNPs were employed to catalyze two, reductive chemical reactions, transforming 4-nitrophenol (4-NP) and hexavalent chromium [Cr(VI)], into 4-aminophenol and Cr(IV), respectively. In the reduction of 4NP, the catalytic performance was directly proportional to PdNP surface area, i.e., the smallest PdNPs in formatePdCH34 cells had the fastest rate of reaction. The mass of Pd(0) as PdNPs was the main contributor to Cr(VI) reduction; the chemically synthesized PdNPs showed the highest removal efficiency with 96% at 20 min. The use of glutaraldehyde enhanced the reduction of Pd(II) and promoted PdNPs formation, i.e., creating an artefact of fixation; however, this treatment also enhanced the catalytic performance of these PdNPs.

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M. Asadipoora, A. Pourkamali Anarakia, J. Kadkhodapoura, S.M.H. Sharifib, A. Barnoushc

ABSTRACT:
The effect of hydrogen on the mechanical properties of X70 pipeline steel was investigated by a combination of macro- and microscale approaches. Various tensile tests under vacuum, in-situ H-plasma charging (IHPC), and ex-situ electrochemical H-charging (EEHC) conditions were conducted to elucidate the hydrogen effect in the macroscale approach. All tensile tests were performed inside an environmental scanning electron microscopy (ESEM) chamber. The IHPC, as a novel hydrogen charging technique, was compared with conventional EEHC while uncharged tensile specimens were used as a reference. The results demonstrated that the variations in the IHPC condition were negligible compared to the vacuum condition, whereas the differences in the ex-situ condition were more prominent. Furthermore, susceptibility to hydrogen in the vacuum-ex situ regime was manifested in the reduction of yield strength and ultimate tensile strength. These findings were confirmed by the fractographic analysis, where some of the effects of hydrogen (e.g. the formation of secondary cracks by detrimental inclusions (MnS and Al2O3) and the transition of fracture features from ductile dimples to cleavage patterns) were well illustrated. On the other hand, micro-cantilever bending tests were performed in the air to avoid hydrogen effects and applied inside a miniaturized electrochemical cell to promote hydrogen uptake. The bending results and post-mortem analysis of the tested cantilevers indicated that the hydrogen-reduced flow stress and hydrogen-induced cracking occurred for the H-charged bent cantilever, while only increased plastic behavior occurred for the cantilever bent in the air.

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Alan Levett, Emma J. Gagen, Hui Diao, Paul Guagliardo, Llew Rintoul, Anat Paz, Paulo M. Vasconcelos, Gordon Southam

ABSTRACT:
Demonstrating the biogenicity of presumptive microfossils in the geological record often requires supporting chemical signatures, including isotopic signatures. Understanding the mechanisms that promote the preservation of microbial biosignatures associated with microfossils is fundamental to unravelling the palaeomicrobiological history of the material. Organomineralization of microorgan- isms is likely to represent the first stages of microbial fossilisation and has been hypothesised to prevent the autolytic degradation of microbial cell envelope structures. In the present study, two distinct fossilisation textures (permineralised microfossils and iron oxide encrusted cell envelopes) identified throughout iron-rich rock samples were analysed using nanoscale secondary ion mass spectrometry (NanoSIMS). In this system, aluminium is enriched around the permineralised micro- fossils, while iron is enriched within the intracellularly, within distinct cell envelopes. Remarkably, while cell wall structures are indicated, carbon and nitrogen biosignatures are not preserved with permineralised microfossils. Therefore, the enrichment of aluminium, delineating these microfossils appears to have been critical to their structural preservation in this iron-rich environment. In contrast, NanoSIMS analysis of mineral encrusted cell envelopes reveals that preserved carbon and nitrogen biosignatures are associated with the cell envelope structures of these microfossils. Interestingly, iron is depleted in regions where carbon and nitrogen are preserved. In contrast aluminium appears to be slightly enriched in regions associated with remnant cell envelope structures. The correlation of aluminium with carbon and nitrogen biosignatures suggests the complexation of aluminium with preserved cell envelope structures before or immediately after cell death may have inactivated autolytic activity preventing the rapid breakdown of these organic, macromolecular structures. Combined, these results highlight that aluminium may play an important role in the preservation of microorganisms within the rock record.

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Alice Bastos S. Fanta, Adam Fuller, Hossein Alimadadi, Matteo Todeschini, Daniel Goran, Andrew Burrows

ABSTRACT:
Transmission Kikuchi Diffraction (TKD) in the scanning electron microscope has been developing at a fast pace since its introduction less than a decade ago. The recently presented on-axis detector configuration, with its optimized geometry, has significantly increased the signal yield and facilitated the acquisition of STEM images in bright field (BF) and dark field (DF) mode, in addition to the automated orientation mapping of nanocrystalline electron transparent samples. However, the physical position of the integrated imaging system, located outside the detector screen, requires its movement in order to combine high resolution STEM images with high re- solution orientation measurements. The difference between the two positions makes it impossible to acquire optimal signals simultaneously, leading to challenges when investigating site-specific nanocrystalline micro- structures. To eliminate this drawback, a new imaging capability was added at the centre of the on-axis TKD detector, thus enabling acquisition of optimal quality BF images and orientation maps without detector move- ment. The advantages brought about by this new configuration are presented and the associated limitations are discussed.

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Jun Li, Guangxu Chen, Yangying Zhu, Zheng Liang, Allen Pei, Chun-Lan Wu, Hongxia Wang, Hye Ryoung Lee, Kai Liu, Steven Chu and Yi Cui

ABSTRACT:
Electrochemical CO₂ reduction is a critical approach to reducing the globally accelerating CO₂ emission and generating value- added products. Despite great efforts to optimize catalyst activity and selectivity, facilitating the catalyst accessibility to high CO₂ concentrations while maintaining electrode durability remains a significant challenge. Here, we designed a catalytic system that mimics the alveolus structure in mammalian lungs with high gas permeability but very low water diffusibility, enabling an array of three-phase catalytic interfaces. Flexible, hydrophobic, nanoporous polyethylene membranes with high gas permeabil- ity were used to enable efficient CO₂ access and a high local alkalinity on the catalyst surface at different CO₂ flow rates. Such an alveolus-mimicking structure generates a high CO production Faradaic efficiency of 92% and excellent geometric current densities of CO production (25.5 mA cm⁻²) at −0.6 V versus the reversible hydrogen electrode, with a very thin catalyst thick- ness of 20−80 nm.

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Stephen M. Elardo, Anat Shahar, Timothy D. Mock, Corliss K. Sio

ABSTRACT: We have conducted high-pressure, high-temperature isotope exchange experiments between molten silicate and molten Fe–Si–C-alloys to constrain the effect of Si on equilibrium Fe isotope fractionation during planetary core formation. The values of ?Δ⁵⁷ Fe_{Metal-Silicate} at 1850 ° C and 1 GPa determined by high-resolution MC-ICP-MS in this study range from −0.013 ± 0.054‰ (2SE) to 0.072 ± 0.085‰ with 1.34–8.14 atom % Si in the alloy, respectively. These results, although not definitive on their own, are consistent with previous experimental results from our group and a model in which elements that substitute for Fe atoms in the alloy structure (i.e., Ni, S, and Si) induce a fractionation of Fe isotopes between molten silicate and molten Fe-alloys during planetary differentiation. Using in situ synchrotron X-ray diffraction data for molten Fe-rich alloys from the literature, we propose a model to explain this fractionation behavior in which impurity elements in Fe-alloys cause the nearest neighbor atomic distances to shorten, thereby stiffening metallic bonds and increasing the preference of the alloy for heavy Fe isotopes relative to the silicate melt. This fractionation results in the bulk silicate mantles of the smaller terrestrial planets and asteroids becoming isotopically light relative to chondrites, with an enrichment of heavy Fe isotopes in their cores, consistent with magmatic iron meteorite compositions. Our model predicts a bulk silicate mantle δ⁵⁷Fe ranging from −0.01‰ to −0.12‰ for the Moon, −0.06‰ to −0.33‰ for Mars, and −0.08‰ to −0.33‰ for Vesta. Independent estimates of the δ⁵⁷Fe of primitive mantle source regions that account for Fe isotope fractionation during partial melting agree well with these ranges for all three planetary bodies and suggest that Mars and Vesta have cores with impurity (i.e., Ni, S, Si) abundances near the low end of published ranges. Therefore, we favor a model in which core formation results in isotopically light bulk silicate mantles for the Moon, Mars, and Vesta. The processes of magma ocean crystallization, mantle partial melting, and fractional crystallization of mantle-derived melts are all likely to result in heavy Fe isotope enrichment in the melt phase, which can explain why basaltic samples from these planetary bodies have variable δ⁵⁷Fe values consistently heavier than our bulk mantle estimates. Additionally, we find no clear evidence that Fe isotopes were fractionated to a detectable level by volatile depletion processes during or after planetary accretion, although it cannot be ruled out.

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M.H. Jomaaa, L. Roibana, D.S. Dhunganaa, J. Xiaoa, J.Y. Cavailléa, L. Seveyratc, L. Lebrunc, G. Diguetb, K. Masenelli-Varlota

ABSTRACT: Electroactive devices are developed for energy conversion purposes. In particular, polyurethanes (PU) are lightweight and flexible materials, which have demonstrated their ability to convert electrical energy into mechanical energy (actuation by electrostriction) and vice-versa (energy harvesting). It has been shown that energy conversion efficiency can be increased by incorporating carbon nanotubes (CNTs) into a PU matrix. The counterpart of this improvement is the stiffness increase, which in turn limits the electrostriction efficiency. On the other hand, it is well known that CNTs are hardly dispersed in a polymeric matrix, and that the interfacial adhesion strength is generally poor. One solution to improve both dispersion and adhesion consists in grafting polymeric chains onto the CNT surfaces. As most of the works dedicated to improve material electroactivity are mainly empirical, this work aims to (i) better characterize these material microstructures by electron tomo- graphy, through the measurement of the CNT tortuosity, the CNT-CNT minimum distance and the number of their contacts, and (ii) and to predict their mechanical stiffness from these microstructural data. From electron microscopy observations of the studied materials, CNTs can be assumed to be composed of successive stiff rods of measured length and orientation, linked together by flexible kinks. Their mechanical stiffening effect in PU is, simply and in an original way, evaluated using the classical analytical equations derived by Halpin and Kardos, accounting for the microstructural parameters determined by electron tomography. It appears clearly that, due to their tortuosity and despite their ultra-high longitudinal stiffness, CNTs only poorly stiffen soft matrices. Fully stretching 10 μm long nanotubes increases the composite modulus by almost 10 for a fraction of only 2 vol%.

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Kristin A. Marshall¹ · Travis W. Walker²

ABSTRACT: A microfluidic device, deemed the Plateau-Rayleigh microfluidic extensional rheometer (PRIMER), is presented that uses a cross-slot geometry to observe a two-phase droplet-breakup event in which the viscoelastic fluid is in the dispersed (or droplet) phase. For viscoelastic fluids, we report that a cylindrical filament forms between droplet segments with a diameter that decays exponentially in time. In optically tracking this decay, both transient extensional viscosity and extensional relaxation times can be evaluated. For validating and optimizing the device, a range of poly(ethylene oxide) (PEO) solutions and Newtonian solutions were tested. Comparisons of the evolution profiles as a result of the presence of elasticity are made, and these results are compared with the results from dripping-onto-a-substrate (DoS), another emerging extensional technique.

¹ School of Chemical, Biological, and Environmental Engineering, Oregon State University, Corvallis, OR, 97331, USA
² Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, 57701, USA

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Ewa Kosmowska¹, Michael Almond², Josh Wong², Brian Law², Barbara Armbruster¹ and Ronald Vane¹

1. XEI Scientific, Inc., Redwood City, CA, USA.
2. Moxtek Inc., Orem, UT, USA.

XEI Scientific Inc. is a recognized manufacturer of plasma cleaners that have been proven to be very effective in removing adventitious hydrocarbon contamination from electron microscope chambers. Over 15 years there are no reports of X-ray window failure or damage to EDS detectors on SEM chambers due to oxygen radicals generated by the Evactron plasma cleaners.

The oxygen radicals created in the plasma oxidize carbon compounds, producing CO, CO2 and H2O, which are then evacuated from the instrument. Quantum chemistry rules regarding energy loss state that these oxygen atoms do not react with diatomic molecules in two body collisions but require a third body to kinetically carry away excess energy. Oxygen radicals also react on solid surfaces such as metals where they can react or recombine with hydrocarbons. Numerous studies performed at XEI Scientific using previously contaminated quartz crystal microbalances to measure cleaning rates have shown that Evactron plasma cleaning is very effective at removing hydrocarbons.

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Barbara Armbruster¹, Stefan Diller², James Grande³ and Ronald Vane¹

1. XEI Scientific, Inc., Redwood City, CA USA
2. Stefan Diller – Scientific Photography, Wuerzburg, Germany
3. General Electric Global Research, Niskayuna, NY USA

XEI has recently invented a new plasma generation technology with RF external hollow cathode excitation. This new Evactron E50 plasma cleaner operates from a lower base pressure compared to previous models and rapidly removes most hydrocarbons from a vacuum chamber. At turbo pump pressures, Evactron cleaning becomes faster and the downstream plasma afterglow spreads throughout the chamber, removing contamination and significantly shortening pump down time, allowing for high throughput of sample processing and analysis.

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Ronald Vane¹, Barbara Armbruster¹, Michael Cable¹, Ewa Kosmowska1 and George Safar¹

1. XEI Scientific, Inc., Redwood City, CA, USA

XEI Scientific invented the Evactron De-Contaminator, a practical plasma cleaning system for Scanning Electron Microscopes (SEMs) in 1999 that could be mounted on the chamber to clean in situ. Plasma cleaners have now become a standard accessory to quickly and effectively remove hydrocarbons from vacuum chambers and specimens. Eliminating hydrocarbons prevents contamination artifacts such as black squares, scan deposits, and carbon peaks in EDS spectra. The Evactron plasma radical source uses a unique RF hollow cathode to create a low-temperature RF plasma in a vacuum that is able to make oxygen radicals from air. These radicals (oxygen atoms) gently combine with hydrocarbons in the vacuum chamber to form CO and H2O gases that are removed by viscous flow to the vacuum pump.

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Ronald Vane¹ and Michael Cable¹

1. XEI Scientific Inc, Redwood City, CA.

Residual Gas Analyzers (RGA) are powerful tools to measure and identify gases and contaminants in vacuum chambers. XEI Scientific has manufactured Evactron® plasma cleaners for SEMs since 1999 to remove hydrocarbon contamination. XEI has recently invented a new plasma generation technology with RF external hollow cathode excitation. This new Evactron E50 plasma cleaner operates from a lower base pressure and rapidly removes most hydrocarbons from a vacuum chamber. Because the E50 model operates at lower pressures, RGA spectra can be obtained quickly after the plasma cleaning is stopped. Previous results documented faster pump down times after plasma cleaning with the E50. Fast pump down allows a RGA spectrum to be taken soon after the plasma is stopped so that hydrocarbons can be monitored before being changed by migration.

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E. S. Steenstra, N. Agmon, J. Berndt, S. Klemme, S. Matveev & W. van Westrenen

ABSTRACT: The depletions of potassium (K) and sodium (Na) in samples from planetary interiors have long been considered as primary evidence for their volatile behavior during planetary formation processes. Here, we use high-pressure experiments combined with laser ablation analyses to measure the sulfide- silicate and metal-silicate partitioning of K and Na at high pressure (P) – temperature (T) and find that their partitioning into metal strongly increases with temperature. Results indicate that the observed Vestan and Martian mantle K and Na depletions can reflect sequestration into their sulfur-rich cores in addition to their volatility during formation of Mars and Vesta. This suggests that alkali depletions are not affected solely by incomplete condensation or partial volatilization during planetary formation and differentiation, but additionally or even primarily reflect the thermal and chemical conditions during core formation. Core sequestration is also significant for the Moon, but lunar mantle depletions of K and Na cannot be reconciled by core formation only. This supports the hypothesis that measured isotopic fractionations of K in lunar samples represent incomplete condensation or extensive volatile loss during the Moon-forming giant impact.

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ANTON A. SMIRNOV, ANDREY AFANASIEV, SERGEY GUSEV, DMITRY TATARSKIY, NICKOLAI ERMOLAEV, AND NIKITA BITYURIN

ABSTRACT: Evolution of the UV-induced absorption within the polymer matrix possessing a highly soluble CdS precursor is studied. The initially optically transparent (polymethylmethacrylate based) samples are irradiated by a light-emitting diode operated at 365 nm for different intensities and different temperatures. In situ monitoring of the process is performed at a wavelength of 405 nm where the samples are initially transparent. The study shows that the increase in absorbance is temperature dependent, and at a fixed temperature it is determined by UV exposure rather than the intensity or irradiation time separately. TEM, HR TEM data, as well as data on absorption and luminescent spectra, allow the relation of the optical absorption evolution to the CdS nanoparticles growth process. This provides new valuable information on the kinetics of this phenomenon in UV irradiated polymer films with a soluble precursor.

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Nhung H. A. Nguyen, Roman Špánek, Vojtěch Kasalický, David Ribas, Denisa Vlková, Hana Řeháková, Pavel Kejzlara and Alena Ševců

ABSTRACT: While nano-scale and micro-scale zero-valent iron (nZVI and mZVI) particles show high potential for reme- diation of polluted soil aquifers and elimination of cyanobacterial blooms, this has required their release into the environment. This study compares the impact of 100 mg L−1 of nZVI and mZVI on natural plank- tonic microorganisms from a reservoir, incubated in 1.5 L batches over 21 days. In addition to counting cyanobacterial and algal cell numbers, bacterial community structure was assessed using Ion Torrent se- quencing and the number of cultivable bacteria determined using standard cultivation methods. Surpris- ingly, while mZVI had no significant effect on algal cell number, cyanobacteria numbers increased slightly after 14 days (P < 0.05). Algae were only marginally affected by nZVI after seven days (P < 0.05), while cyanobacteria numbers remained unaffected after 21 days. Total species richness and less common bacte- ria increased significantly when treated with mZVI (compared to nZVI). The abundance of Limnohabitans (Betaproteobacteria), Roseiflexus (Chloroflexi), hgcl_clade (Actinobacteria) and Comamonadaceae_unclassified (Betaproteobacteria) increased under nZVI treatment, while mZVI enhanced Opitutae_vadinHA64 (Verrucomicrobia) and the OPB35_soil_group (Verrucomicrobia). Interestingly, the number of cultivable bacteria increased significantly after three days in water with nZVI, and further still after seven days. nZVI shaped bacterial community both directly, through release of FeIJII)/FeIJIII), and indirectly, through rapid oxygen consumption and establishment of reductive conditions. The strong physico-chemical changes caused by nZVI proved temporary; hence, it can be assumed that, under natural conditions in resilient reservoirs or lakes, microbial plankton would recover within days or weeks.

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Alice Bastos Fanta⁎, Matteo Todeschini, Andrew Burrows, Henri Jansen, Christian D. Damsgaard, Hossein Alimadadi, Jakob B. Wagner

ABSTRACT: Transmission Kikuchi diffraction (TKD) facilitates automated orientation mapping of thin films in scanning electron microscopes (SEM). In this study TKD is applied for the first time to perform in-situ annealing ex- periments on gold thin films deposited on a MEMS-based heating system. The very local heating associated with this system enables reliable TKD measurements at elevated temperatures without notable disturbance from infrared radiation. The dewetting of an Au thin film into Au nanoparticles upon heating is followed with or- ientation mapping in a temperature range between 20 °C and 900 °C. The local thickness variation associated with the dewetting is observed qualitatively by observing the intensity of the transmitted beam, which decreases as the film thickness increases locally. The results of this study reveal that TKD is a well suited technique to study thin-film stability and solid state dewetting. Moreover, the outcome of this methodological study provides a baseline for further in-situ crystallographic studies of electron transparent samples in the SEM.

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Michael T. Postek and András Vladár , NIST, Gaithersburg, MD
Proc SPIE Int. Soc. Opt. Eng. Vol. 9636: 963605 (2015)

Abstract: This is the fourth part of a series of tutorial papers discussing various causes of measurement uncertainty in scanned particle beam instruments, and some of the solutions researched and developed at NIST and other research institutions. Scanned particle beam instruments, especially the scanning electron microscope (SEM), have gone through tremendous evolution to become indispensable tools for many and diverse scientifc and industrial applications. These improvements have significantly enhanced their performance and made them far easier to operate. But, the ease of operation has also fostered operator complacency. In addition, the user-friendliness has reduced the apparent need for extensive operator training. Unfortunately, this has led to the idea that the SEM is just another expensive “digital camera” or another peripheral device connected to a computer and that all of the problems in obtaining good quality images and data have been solved. Hence, one using these instruments may be lulled into thinking that all of the potential pitfalls have been fully eliminated and believing that, everything one sees on the micrograph is always correct. But, as described in this and the earlier papers, this may not be the case. Care must always be taken when reliable quantitative data are being sought. The first paper in this series discussed some of the issues related to signal generation in the SEM, including instrument calibration, electron beam-sample interactions and the need for physics-based modeling to understand the actual image formation mechanisms to properly interpret SEM images. The second paper has discussed another major issue confronting the microscopist: specimen contamination and methods to eliminate it. The third paper discussed mechanical vibration and stage drift and some useful solutions to mitigate the problems caused by them, and here, in this the fourth contribution, the issues related to specimen “charging” and its mitigation are discussed relative to dimensional metrology.

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Michael T. Postek, András Vladár and Kavuri P. Purushotham , NIST, Gaithersburg, MD
SCANNING Vol. 36: 347-355 (2014)

Summary: The scanning electron microscope (SEM) has gone through a tremendous evolution to become indispensable for many and diverse scientific and industrial applications. The improvements have signifi- cantly enriched and augmented the overall SEM performance and have made the instrument far easier to operate. But, the ease of operation also might lead, through operator complacency, to poor results. In addition, the user friendliness has seemingly reduced the need for thorough operator training for using these complex instruments. One might then conclude that the SEM is just a very expensive digital camera or another peripheral device for a computer. Hence, a person using the instrument may be lulled into thinking that all of the potential pitfalls have been eliminated and they believe everything they see on the micrograph is always correct. But, this may not be the case. An earlier paper (Part 1), discussed some of the potential issues related to signal generation in the SEM, instrument calibration, electron beam interactions and the need for physics-based modeling to understand the actual image formation mechanisms. All these were summed together in a discussion of how these issues effect measurements made with the instrument. This second paper discusses another major issue confronting the microscopist: electron-beam-induced specimen contamination. Over the years, NIST has done a great deal of research into the issue of sample contamination and its removal and elimination and some of this work is reviewed and discussed here.

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Michael T. Postek and András Vladár , NIST, Gaithersburg, MD
SCANNING Vol. 35: 355-361 (2013)

Summary: The scanning electron microscope (SEM) has gone through a tremendous evolution to become a critical tool for many and diverse scientific and industrial applications. The high resolution of the SEM is especially suited for both qualitative and quantitative applications especially for nanotechnology and nanomanufacturing. Quantitatively, measurement, or metrology is one of the main uses. It is likely that one of the first questions asked before even the first scanning electron micrograph was ever recorded was: “… how big is that?” The quality of that answer has improved a great deal over the past few years especially since today these instruments are being used as a primary measurement tool on semiconductor processing lines to monitor the manufacturing processes. The well‐articulated needs of semiconductor production prompted a rapid evolution of the instrument and its capabilities. Over the past 20 years or so, instrument manufacturers, through substantial semiconductor industry investment of research and development (R&D) money, have vastly improved the performance of these instru- ments. All users have benefited from this investment, especially where quantitative measurements with an SEM are concerned. But, how good are these data? This article discusses some of the most important aspects and larger issues associated with imaging and measurements with the SEM that every user should know, and understand before any critical quantitative work is attempted.

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James Bishop, Marco Fronzi, Christopher Elbadawi, Vikram Nikam, Joshua Pritchard, Johannes E. Fröch, Ngoc My Hanh Duong, Michael J. Ford, Igor Aharonovich, Charlene J. Lobo and Milos Toth

ABSTRACT: Diamond is an ideal material for a broad range of current and emerging applications in tribology, quantum photonics, high-power electronics, and sensing. However, top-down processing is very challenging due to its extreme chemical and physical properties. Gas-mediated electron beam-induced etching (EBIE) has recently emerged as a minimally invasive, facile means to dry etch and pattern diamond at the nanoscale using oxidizing precursor gases such as O2 and H2O. Here we explain the roles of oxygen and hydrogen in the etch process and show that oxygen gives rise to rapid, isotropic etching, while the addition of hydrogen gives rise to anisotropic etching and the formation of topographic surface patterns. We identify the etch reaction pathways and show that the anisotropy is caused by preferential passivation of specific crystal planes. The anisotropy can be controlled by the partial pressure of hydrogen and by using a remote RF plasma source to radicalize the precursor gas. It can be used to manipulate the geometries of topographic surface patterns as well as nano- and microstructures fabricated by EBIE. Our findings constitute a comprehensive explanation of the anisotropic etch process and advance present understanding of electron-surface interactions.

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Gayan C. Bandara, Christopher A. Heist, Vincent T. Remcho

ABSTRACT: Membrane based microfluidic devices have gained much popularity in recent years, as they make possible rapid, inexpensive analytical techniques that can be applied to a wide variety of areas. The ability to modify device hydrophilicity and hydrophobicity is critically important in fabricating membrane based microfluidic devices. Polar hydrophilic membranes, such as glass microfiber (GMF) membranes, hold great potential as they are inexpensive, chemically inert, and stable. Filling of these membranes with non-polar polymers such as polycaprolactone (PCL) converts the hydrophilic GMF into a hydrophobic medium. Controlled alteration of the surface chemistry of PCL/GMF substrates allows for the fabrication of microfluidic patterns on the surface. Using this approach, we have developed a simple and rapid technique for fabrication of highly adaptable complex multidimensional (2D and 3D) microfluidic pathways on a single membrane. PCL-filled GMF media were masked and selectively exposed to oxygen radicals so that the exposed surface became permanently superhydrophilic in its behavior. The desired microfluidic pattern was cut into the mask prior to assembly and exposure, and the mask was removed after exposure to reveal the ready-to-use microfluidic device. To verify and demonstrate the performance of this novel fabrication method, a colorimetric total protein assay was applied to the determination of protein concentrations in real samples.

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G.S. Was, S. Taller, Z. Jiao, A.M. Monterrosa, D. Woodley, D. Jennings, T. Kubley, F. Naab, O. Toader, E. Uberseder

ABSTRACT: The widely experienced problem of carbon uptake in samples during ion irradiation was systematically investigated to identify the source of carbon and to develop mitigation techniques. Possible sources of carbon included carbon ions or neutrals incorporated into the ion beam, hydrocarbons in the vacuum sys- tem, and carbon species on the sample and fixture surfaces. Secondary ion mass spectrometry, atom probe tomography, elastic backscattering spectrometry, and principally, nuclear reaction analysis, were used to profile carbon in a variety of substrates prior to and following irradiation with Fe2+ ions at high temperature. Ion irradiation of high purity Si and Ni, and also of alloy 800H coated with a thin film of alumina eliminated the ion beam as the source of carbon. Hydrocarbons in the vacuum and/or on the sample and fixtures was the source of the carbon that became incorporated into the samples during irra- diation. Plasma cleaning of the sample and sample stage, and incorporation of a liquid nitrogen cold trap both individually and especially in combination, completely eliminated the uptake of carbon during heavy ion irradiation. While less convenient, coating the sample with a thin film of alumina was also effective in eliminating carbon incorporation.

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Andrew J. Breen, Katharina Babinsky, Alec C. Day, K. Eder, Connor J. Oakman, Patrick W. Trimby,Sophie Primig, Julie M. Cairney and Simon P. Ringer

ABSTRACT: Correlative microscopy approaches offer synergistic solutions to many research problems. One such combination, that has been studied in limited detail, is the use of atom probe tomography (APT) and transmission Kikuchi diffraction (TKD) on the same tip specimen. By combining these two powerful microscopy techniques, the microstructure of important engineering alloys can be studied in greater detail. For the first time, the accuracy of crystallographic measurements made using APT will be independently verified using TKD. Experimental data from two atom probe tips, one a nanocrystalline Al–0.5Ag alloy specimen collected on a straight flight-path atom probe and the other a high purity Mo specimen collected on a reflectron-fitted instrument, will be compared. We find that the average minimum misorientation angle, calculated from calibrated atom probe reconstructions with two different pole combinations, deviate 0.7° and 1.4°, respectively, from the TKD results. The type of atom probe and experimental conditions appear to have some impact on this accuracy and the reconstruction and measurement procedures are likely to contribute further to degradation in angular resolution. The challenges and implications of this correlative approach will also be discussed.

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Yuji Tanaka1, Takako Yamashita, and Masayasu Nagoshi

ABSTRACT: Hydrocarbon contamination introduced during point, line and map analyses in a field emission electron probe microanalysis (FE-EPMA) was investigated to enable reliable quantitative analysis of trace amounts of carbon in steels. The increment of contamination on pure iron in point analysis is proportional to the number of iterations of beam irradi- ation, but not to the accumulated irradiation time.

Benoît Kalman, Catherine Picart, and Thomas Boudou

ABSTRACT: Over the past decade, a major effort was made to miniaturize engineered tissues, as to further improve the throughput of such approach. Most existing methods for generating microtissues thus rely on T-shaped cantilevers made by soft lithography and based on the use of negative SU-8 photoresist. However, photopatterning T-shaped microstructures with these negative photoresists is fastidious and time-consuming.

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Zhen Li, Sisi Yang, Rohan Dhall, Ewa Kosmowska, Haotian Shi, Ioannis Chatzakis, and Stephen B. Cronin

ABSTRACT: We report Raman and photoluminescence spectra of mono- and few-layer WSe2 and MoSe2 taken before and after exposure to a remote oxygen plasma. For bilayer and trilayer WSe2, we observe an increase in the photoluminescence intensity and a blue shift of the photoluminescence peak positions after oxygen plasma treatment. The photoluminescence spectra of trilayer WSe2 exhibit features of a bilayer after oxygen plasma treatment.

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Rohan Dhall, Kyle Seyler, Zhen Li,Darshana Wickramaratne, Mahesh R. Neupane, Ioannis Chatzakis, Ewa Kosmowska, Roger K. Lake, Xiaodong Xu, and Stephen Cronin

ABSTRACT: We report circularly polarized photoluminescence spectra taken from few layer MoS2 after treatment with a remotely generated oxygen plasma. Here, the oxygen plasma decouples the individual layers in MoS2 by perturbing the weak interlayer van der Waals forces without damaging the lattice structure.

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Abdel-Aziz El Mel,  Nicolas Stephan,  Jonathan Hamon,  Damien Thiry, Adrien Chauvin, Meriem Chettab, Eric Gautron, Stephanos Konstantinidis, Agnès Graniera  and Pierre-Yves Tessiera

Nanoporous materials are of great importance for a broad range of applications including catalysis, optical sensors and water filtration. Although several approaches already exist for the creation of nanoporous materials, the race for the development of versatile methods, more suitable for the nanoelectronics industry, is still
ongoing.

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Rohan Dhall , Mahesh R. Neupane , Darshana Wickramaratne , Matthew Mecklenburg , Zhen Li , Cameron Moore , Roger K. Lake, and Stephen Cronin

2D materials, such as graphene and few-layer transition metal dichalcogenides (TMDCs), have attracted great research interest in the past decade, since mechanical exfoliation of these materials from their 3D bulk counterparts was demonstrated.

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András E. Vladár*, Michael T. Postek* and Ronald Vane**, *National Institute of Standards and Technology, Gaithersburg, MD **XEI Scientific, Inc., Redwood City, CA
Presentation at SPIE Microlilthography Conference Feb 27-28, 2001; Proc SPIE, Vol. 4344(2001): 835.

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Neal Sullivan*, Tung Mai*, Scott Bowdoin*, and Ronald Vane**, *Schlumberger Technologies, 45 Winthrop St., Concord, MA **XEI Scientific, Inc., Redwood City, CA
Presentation at Microscopy and Microanalysis Meeting, August, 2002, Quebec City, Canada (Microscopy& Microscroanalysis Vol. 8, Supplement 2, 720CD)

A complete paper with CD SEM data.

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András E. Vladár, K. P. Purushotham and Michael T. Postek, NIST, Gaithersburg, MD
Presented at SPIE Advanced Microlithograpy Feb 2008, San Jose, CA

Electron beam-induced contamination is becoming one of the most bothersome problems of the scanning electron microscopes. Even in clean-vacuum instruments it is possible that the image gradually darkens because a polymerized hydrocarbon layer with low secondary electron yield is deposited. This contamination layer can get so thick that it changes the size and shape of the small structures of current and future state-of-the art ICs. This greatly disturbs the measurement process and the erroneous results can lead to wrong process control decisions. NIST has developed cleaning procedures and a viable contamination specification that offer an effective solution for this problem.

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Christopher G. Morgan*, Patrick P. Naulleau**, Senajith B. Rekawa**, Paul E. Denham**, Brian H. Hoef**, Michael S. Jones**, and Ronald Vane*, *XEI Scientific, Inc., 1755 E. Bayshore Blvd., Redwood City, CA, **Center for X-Ray Optics (CXRO), Lawrence Berkeley National Laboratory, Berkeley, CA
Poster Presentation at SPIE Advanced Lithography Conference, February 2010, San Jose, CA

The problem of carbon contamination on extreme ultraviolet (EUV) optics, causing unacceptably low reflectivity in mirrors, must be solved before industry will adopt the technology on a production scale. The quantity of oxygen radicals produced by the low-power downstream plasma cleaner is sufficient to remove contamination from EUV optics as demonstrated by the experiments. Additionally, EUV reflectance measurements show that this method of cleaning optics does not reduce the reflectivity of the optic through formation of an oxide on the capping layer of the optic.

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