Carbon Contamination – Science Papers
Publications about contamination and the effectiveness of the Evactron system
THE SCIENTIFIC BACKGROUND
In SEMs, FIBs, and TEMs, contamination is a serious problem for specimen analysis and the production of high-resolution images. Beam-induced carbonaceous material is deposited on the region under study, causing loss of resolution. Hydrocarbon contamination causes the image darkening or “Black Square” in a typical SEM image. The Evactron De-Contaminator removes hydrocarbon contamination from electron microscopes. A radio frequency (RF) generated plasma is attached to the microscope vacuum chamber. Room air or other oxygen containing gas passes through the plasma, producing oxygen radicals in situ. These radicals clean organic contaminants from the interior of vacuum systems and sample surfaces. The oxygen radicals decompose carbon-containing material into H2O, CO, and CO2, which are evacuated from the system.
Preparation of atom probe tips from (nano)particles in dispersion using (di)electrophoresis and electroplating
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.
The characterisation of dental enamel using transmission Kikuchi diffraction in the scanning electron microscope combined with dynamic template matching
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.
3D-printed plasma-treated super-amphiphilic microgroove surface for outperformance of liquid vertical transportation
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.
Bacteria conjugate ubiquitin-like proteins to interfere with phage assembly
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.
Effect of deformation temperature on strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C low-density steel
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.
Morphology and nanostructure of soot particles from diesel engine under transient and steady-state operating conditions with a microalgae fuel component, dioctyl phthalate biofuel
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.
The Temperature-Dependent Phase Transformation and Microstructural Characterisation in In-Sn Solder Alloys
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.
Scalable Substrate Development for Aqueous Biological Samples for Atom Probe Tomography
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.
Electron microscopy approach to the wetting dynamics of single organosilanized mesopores
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.
Influence of the catalyst layer thickness on the determination of the OER activity of Fe304@C0Fe204 core-shell nanoparticles
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.
Historical diamond mine waste reveals carbon sequestration resource in kimberlite residue
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.
Influence of microscope settings on dislocation imaging in transmission forescattered electron imaging (t-FSEI)
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.
Microstructure-Property Correlation and Its Evolution during Aging in an Al4.4Co26Cr19Fe18Ni27Ti5.6 High-Entropy Alloy
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.
Evaluation of hydrogen effect on the fatigue crack growth behavior of medium-Mn steels via in-situ hydrogen plasma charging in an environmental scanning electron microscope
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.
Hydrogen-enhanced fatigue crack growth in a single-edge notched tensile specimen under in-situ hydrogen charging inside an environmental scanning electron microscope
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.
UV-Induced Gold Nanoparticle Growth in Polystyrene Matrix with Soluble Precursor
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.
Havre 2012 pink pumice is evidence of a short- lived, deep-sea, magnetite nanolite-driven explosive eruption
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.
Hydrogen and deuterium charging of lifted-out specimens for atom probe tomography
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.
Historical diamond mine waste reveals carbon sequestration resource in kimberlite residue
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.
Accelerated mineral carbonation of coarse residue kimberlite material by inoculation with photosynthetic microbial mats
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.
Rescuing Tetracycline Class Antibiotics for the Treatment of Multidrug-Resistant Acinetobacter baumannii Pulmonary Infection
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.
Neurodegenerative Disease Treatment Drug PBT2 Breaks Intrinsic Polymyxin Resistance in Gram-Positive Bacteria
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.
Electron Probe Microanalysis of Transition Metals using L lines: The Effect of Self-absorption
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.
Havre 2012 pink pumice is evidence of a shortlived, deep-sea, magnetite nanolite-driven explosive eruption
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.
High resolution crystal orientation mapping of ultrathin films in SEM and TEM
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.
Neurodegenerative Disease Treatment Drug PBT2 Breaks Intrinsic Polymyxin Resistance in Gram-Positive Bacteria
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.
Biophysical properties of hydrogels for mimicking tumor extracellular matrix
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.
Streptococcus pyogenes Hijacks Host Glutathione for Growth and Innate Immune Evasion
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.
Dysregulation of Streptococcus pneumoniae zinc homeostasis breaks ampicillin resistance in a pneumonia infection model
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.
The Role of Co-injected Helium on Swelling and Cavity Evolution at High Damage Levels in Ferritic-Martensitic Steels
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.
Effect of reflected Ar neutrals on tantalum diboride coatings prepared by direct current magnetron sputtering
ABSTRACT:
The magnetron sputtered tantalum diboride (TaBy) 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 TaBy 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.
A novel granular sludge-based and highly corrosion-resistant bio-concrete in sewers
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.
PLGA encapsulated γ-cyclodextrin-meropenem inclusion complex formulation for oral delivery
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.
Liquid CO2 Formulated Mesoporous Silica Nanoparticles for pH-Responsive Oral Delivery of Meropenem
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.
Attached and planktonic bacterial communities on bio-based plastic granules and micro-debris in seawater and freshwater
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.
Enhanced metal recovery by efficient agglomeration of precipitates in an up-flow fixed-bed bioreactor
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.
Durability characterization of mechanical interfaces in solar sail membrane structures
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.
Electrochemical preparation and homogenization of face-centered FeCoNiCu medium entropy alloy electrodes enabling oxygen evolution reactions
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.
Monitoring Carbon in Electron and Ion Beam Deposition within FIB-SEM
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.
Mitigation of laser-induced contamination in vacuum in high-repetition-rate high-peak-power laser systems
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.
Tungsten Probe Tip Cleaning
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.
Plasma Cleaning with Alternate Gases
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.
The Benefits of Plasma Cleaning for TKD/EBSD Analysis
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.
Influence of spinodal decomposition and fcc → w phase transformation on global and local mechanical properties
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.
Structure evolution and mechanical properties of hard tantalum diboride films
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.
Radiation-Induced Damage and Recovery of Ultra Nano-Crystalline Diamond
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.
Schottky Contacts on Polarity-Controlled Vertical ZnO Nanorods
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.
A novel calcium-concentrating compartment drives biofilm formation and persistent infections
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.
Nanoparticle elasticity regulates phagocytosis and cancer cell uptake
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.
Biochemical synthesis of palladium nanoparticles
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.
Macro- and microscale investigations of hydrogen embrittlement in X70 pipeline steel
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.
The role of aluminium in the preservation of microbial biosignatures
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.
Improving the imaging capability of an on-axis transmission Kikuchi detector
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.
Efficient electrocatalytic CO2 reduction on a three-phase interface
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.
The effect of core composition on iron isotope fractionation between planetary cores and mantles
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 FeMetal-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.
Quantitative analysis of grafted CNT dispersion and of their stiffening of polyurethane (PU)
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%.
Investigating the dynamics of droplet breakup in a microfluidic cross-slot device for characterizing the extensional properties of weakly-viscoelastic fluids
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
Advancements of Evactron® Plasma Cleaning of Moxtek® X-ray Windows
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.
Visualizing Evactron® Turbo PlasmaTM Cleaning in nanoflight® Movies
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.
20th Anniversary of Evactron® Plasma Cleaners for SEMs and FIBs
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.
Using a Residual Gas Analyzer to Monitor Plasma Cleaning of SEM Chambers and Specimens
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.
Depletion of potassium and sodium in mantles of Mars, Moon and Vesta by core formation
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.
Exposure dependence of the UV initiated optical absorption increase in polymer films with a soluble CdS precursor and its relation to the photoinduced nanoparticle growth
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.
Different effects of nano-scale and micro-scale zero-valent iron particles on planktonic microorganisms from natural reservoir water
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.
Elevated temperature transmission Kikuchi diffraction in the SEM
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.
Does Your SEM Really Tell the Truth? – How Would You Know? Part 4
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.
Does Your SEM Really Tell the Truth? – How Would You Know? Part 2
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.
Does Your SEM Really Tell the Truth? – How Would You Know? Part 1
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.
Deterministic Nanopatterning of Diamond Using Electron Beams
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.
Patterned polycaprolactone-filled glass microfiber microfluidic devices for total protein content analysis
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.
Resolution of the carbon contamination problem in ion irradiation experiments
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.
Correlating Atom Probe Crystallographic Measurements with Transmission Kikuchi Diffraction Data
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.
Quantitative FE-EPMA measurement of formation and inhibition of carbon contamination on Fe for trace carbon analysis
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.
Quick and easy microfabrication of T-shaped cantilevers to generate arrays of microtissues
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.
Layer Control of WSe2 via Selective Surface Layer Oxidation
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.
Strong Circularly Polarized Photoluminescence from Multilayer MoS2 2 Through Plasma Driven Direct-Gap Transition
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.
Creating nanoporosity in silver nanocolumns by direct exposure to radio-frequency air plasma
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.
Direct Bandgap Transition in Many-Layer MoS 2 by Plasma-Induced Layer
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.
Active Monitoring and Control of Electron Beam Induced Contamination
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.
A Study of the Effectiveness of the Removal of Hydrocarbon Contamination by Oxidative Cleaning Inside the SEM
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.
Contamination Specification for Dimensional Metrology SEMs
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.
Removal of Surface Contamination from EUV Mirrors using Low-Power Downstream Plasma Cleaning
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.
Cleaning of Capped Multi-Layer Samples and Cleaning with Hydrogen using the Evactron® De-Contaminator
Christopher G. Morgan and Ronald Vane*, XEI Scientific, Inc., 1755 E. Bayshore Blvd., Redwood City, CA
Presentation at the EUV Lithography Workshop, June 2011, Maui, Hawaii
Carbon contamination on extreme ultraviolet (EUV) optics reduces their reflectivity. Further studies of the effect cleaning multilayer blanks capped with either silicon or ruthenium by the Evactron system are presented. Room air and argon/oxygen mixtures are used as the cleaning gas. EUV reflectivity of the blanks and surface roughness are measured post cleaning to determine if the cleaning process is both effective and not harmful. Preliminary data shows that the oxygen mixtures are very effective at removing PMMA resist from a silicon wafer. Additionally the use of hydrogen gas with the Evactron De-Contaminator is explored. Optical emission spectra of the plasma show that hydrogen radicals are created by the Evactron system. Cleaning effectiveness can be determined by using quartz crystal microbalances. The hydrogen atoms remove carbon contamination with maximum cleaning occurring at 100 mTorr chamber pressure. Rates around 1 nm per minute have been measured when the Evactron system is 15 cm from the quartz crystal microbalance.
Contamination-Free Transmission Electron Microscopy for High-Resolution Carbon Elemental Mapping of Polymers
Shin Horiuchi*, Takeshi Hanada**, Masaharu Ebisawa**, Yasuhiro Matsuda***, Motoyasu Kobayashi***, and Atsushi Takahara***,*AIST, Ibaraki, Japan, **Consulting Zero Loss Imaging, Tokyo, Japan ***Institute for Materials Chemistry and Engineering, Fukuoka, Japan
ACS Nano, 2009, 3(5), pp 1297-1304 Microscopy and Microanalysis Meeting Aug 2008
This study utilizes the Evactron® D-C for TEMs. The “contamination-free TEM” allowed researchers to accomplish high-resolution carbon elemental mapping by energy-filtered transmission electron microscopy (EFTEM) on the nanostructure of soft materials. In addition, this study illustrates that although TEM cryo-observation is known to be effective in reducing specimen damage, it was not observed to help in carbon mapping, suggesting that the cooling of the specimen may actually increase the contamination deposition rate. In the case of polymers, the detection of carbon is much simpler than those of other light elements because of its high content. Being able to do carbon analysis by elemental mapping and EELS with high spatial resolution without problematic contamination could lead to improvements for various soft-material nanoanalyses by EFTEM. This study suggests that the analytical technique utilizing the “contamination-free TEM” also offers possibilities in studies requiring extended exposure time of the electron beam, such as EELS, nanobeam diffraction and electron tomography.
Remote Plasma Cleaning from a TEM Sample Holder with an Evactron De-Contaminator
Christopher G. Morgan, David Varley, and Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Poster Presentation at Microscopy and Microanalysis Meeting, August 2010, Portland, OR
A new method for using the Evactron D-C to clean TEMs is reported. The RF electrode used to create the oxygen radicals is now mounted on the end of a TEM sample rod. The impedance matching network and gas delivery hardware are placed on the other end of the sample rod, which is hollow to allow oxygen containing gas to reach the electrode.
The Use of Oxygen in SEM Plasma Cleaning Equipment
Thomas O. Mueller, J. Cowan, and E. Swanson, ON Semiconductor, Gresham Failure Analysis Laboratory, Gresham, OR
Poster Presentation at Microscopy and Microanalysis Meeting, August, 2007, Ft. Lauderdale, FL
Comparing the Effects of Different Gas Mixtures and Vacuum Chamber Geometries on the Evactron Cleaning Process
Christopher G. Morgan and Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Poster Presentation at Microscopy and Microanalysis Meeting, August 2008, Albuquerque, NM.
Using a quartz crystal microbalance (QCM), the effectiveness of the Evactron® process has been quantified in this study, as a function of cleaning parameters such as chamber pressure during cleaning, RF power, and distance from the plasma source. The QCM measurements can now be extended in order to consider the effect of different gas mixtures and chamber geometries on cleaning.
Removal of Carbon Contamination using Hydrogen with Low-Power Downstream Plasma Cleaning
C. G. Morgan and R. Vane, XEI Scientific, Inc., Redwood City, CA
Poster Presentation at SPIE Advanced Lithography Conference, March 2011, San Jose, CA
Carbon contamination on extreme ultraviolet (EUV) optics reduces their reflectivity. The use of a commercially available low power downstream plasma cleaner using room air has been shown to be effective in removing carbon contamination from EUV optics. However,there is concern that removal of carbon contamination by oxidation may damage the capping layers of the optics. In particular, ruthenium capping layers may be susceptible to reaction with oxygen radicals. The previous experiments with low power downstream plasma were done on silicon capped EUV optics. In this paper, the use of gases other than room air, such as hydrogen with low power downstream plasma cleaning is explored to determine its effectiveness by using customized quartz crystal monitors.
Non-Destructive Cleaning of Carbon Nanotube Surfaces: Removal of Organic Contaminants and Chemical Residue with Oxygen Radicals
Mihail P. Petkov, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA
Presentation at Microscopy and Microanalysis Meeting, August, 2004, Savannah, GA
Oxygen radicals (OR) have been used as a surface cleaning method for a diverse range of materials. However, the application of OR cleaning to graphite and carbon nanotubes is not straightforward, as oxygen plasma is known to ash both forms of carbon. This work demonstrates a successful OR cleaning of surface organic contaminants (most likely hydrocarbons from the air), as well as chemical residue from the fabrication process, without inducing microstructural changes visible by SEM. An Evactron Decontaminator was used for the study.
Minimization of Hydrocarbon Accumulation on Nanomanipulator Probe Tips
G. McMahon,* Christopher G.. Morgan,** and Ronald Vane** *Nanofabrication Cleanroom Facility, Boston College, Newton, MA 02459, **XEI Scientific, Inc., Redwood City, CA 94063
Poster Presentation at the 2010 Kleindiek User’s Group Meetand and the Microscopy and Microanalysis Meeting, August 2010, Portland, OR
A very positive effect of Evactron downstream plasma cleaning in the prevention of hydrocarbon buildup in nanomanipulator probe tips is reported in this poster.
A Study of the Effects of Evactron® Plasma Cleaning on X-ray Windows
Ronald Vane*, Christine Roberts**, and Vince Carlino* *XEI Scientific, Inc., Redwood City, CA 94063 **Formerly with MOXTEK, Inc., Orem, UT 84057
Presentation at Microscopy and Microanalysis Meeting, August, 2004, Savannah, GA
A complete paper showing that long term cleaning of ultra thin windows (UTW) does not cause window failure.
Effect of Evactron® Cleaning on EBSD Detector Phosphor Screens
Mark Nave* and Andrew Sullivan**, *Microanalysis Consulting Pty. Ltd., St Albans Park, Victoria, Australia
**Centre for Material and Fibre Innovation, Deakin University, Geelong, Victoria, Australia
Improved Carbon Analysis with Evactron Plasma Cleaning
Pierre Rolland*, Vincent L. Carlino**, and Ronald Vane**, *Alprimage, 11 rue de Savoie, 91940 Les Ulis, France, **XEI Scientific, 1735 East Bayshore Rd., Suite 29A, Redwood City, CA 94063, USA
Presentation at Microscopy and Microanalysis Meeting, August, 2004, Savannah, GA
A complete paper on EDS analysis of carbon.
Vapor-Phase Cutting of Carbon Nanotubes Using a Nanomanipulator Platform
Vladimir Mancevski, President and CTO, Xidex Corporation; Philip D. Rack, Professor, The University of Tennessee at Knoxville
Presented at the 2010 Materials Science and Technology Conference, October 2010, Houston, TX
Xidex has developed the NanoBot® nanomanipulator, which can be used as a vapor-phase cutting system to etch carbon nanotubes. They report (see slide 19) that plasma cleaning using the Evactron De-Contaminator inside the SEM chamber can reduce competitive carbon deposition and enhance etching.
Environmental Contamination Sources and Control in High Resolution Scanning Electron Microscopy
Ronald Vane and Vince Carlino, XEI Scientific, Inc., Redwood City, CA
Presentation at Microscopy and Microanalysis Meeting, August, 2005, Honolulu, HI
Hydrocarbon (HC) background and contamination is hard to avoid in our carbon based world. Even with the most careful handling carbon contamination artifacts from Airborne Molecular Contamination (AMC) can creep in and interfere with imaging and measurement in e-beam instruments. The Evactron De-Contaminator made by XEI Scientific is a tool that actively removes HC from the vacuum system and specimens within it to prevent these problems.
(PDF document unavailable.)
Immobilization and Removal of Hydrocarbon Contamination Using the Evactron®De-Contaminator
Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Presentation at Microscopy and Microanalysis Meeting, July-August, 2006, Chicago, IL
Comparison of Residual Gas Analysis results on the removal of volatile components and visual observance of the removal of Hydrocarbon films indicates that the immobilization of Hydrocarbons on surfaces by polymerization using the Evactron De-Contaminator is also an important mechanism for reducing contamination interference with imaging in electron microscopy.
Effect of Cleaning Parameters on Cleaning Effectiveness in a SEM Equipped with an Oxygen Plasma Etching Device
R. Garcia*, A.D. Batchelor*, C.B. Mooney*, A.D. Garetto*, V.L. Carlino**, R. Vane**, and D.P. Griffiths *Materials Science and Engineering Department and Analytical Instrumentation Facility, North Carolina State University, Raleigh, NC; **XEI Scientific, Redwood City, CA 94063
Poster Presentation at Microscopy and Microanalysis Meeting, August, 2007, Ft. Lauderdale, FL
Quantification of Contamination Using Quartz Crystal Thickness Monitors
Christopher G. Morgan, Mark M. Gleason and Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Poster Presentations at Microscopy and Microanalysis Meeting, August, 2007, Ft. Lauderdale, FL
Quartz crystal microbalances (QCMs) are a standard tool for vacuum deposition measurements. They can also be adapted to measure contamination removal by plasma cleaning. Here, they are used to record a thickness loss rate of an oil layer previously deposited on their surface; this loss rate is a measure of the cleaning effectiveness of the Evactron Decontaminator.
Using Thickness Monitor to Measure Contaminant Removal by Evactron Cleaning as a Function of Operating Parameters
Christopher G. Morgan, Mark M. Gleason and Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Poster Presentations at Microscopy and Microanalysis Meeting, August, 2007, Ft. Lauderdale, FL
Quartz crystal microbalances (QCMs) are a standard tool for vacuum deposition measurements. They can also be adapted to measure contamination removal by plasma cleaning. Here, they are used to record a thickness loss rate of an oil layer previously deposited on their surface; this loss rate is a measure of the cleaning effectiveness of the Evactron Decontaminator.
Contamination Removal Rates Improved by New Impedance Matching Network for the Evactron® De-Contaminator
Christopher G. Morgan and Ronald Vane, XEI Scientific, Inc., Redwood City, CA
Paper presented at SPIE Advanced Lithography Conference Feb. 14, 2012, San Jose CA.
Many lithographic tools require carbon-free vacuum environments. A commercially available low-power (<20W) downstream plasma system which produces oxygen radicals in the 0.2-0.6 Torr pressure range has been shown to be effective in removing carbon contamination from standard SEM and FIB tools. However, in larger systems such as wafer or mask inspection tools the extent of cleaning in this pressure range is limited. A new downstream plasma system optimized for larger chambers has been developed which operates at higher power and lower pressure. Cleaning rates of over 1 nm/minute have been measure from over 0.5 m away from the plasma source.
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