Scanning Auger Microscopy Research Articles

Revelations and Translations, Volume 5: Original Manuscript of the Book of Mormon

Revelations and Translations, Volume 5: Original Manuscript of the Book of Mormon

Optical properties, band structures, and phase transition of UO2+x epitaxial films deposited by polymer-assisted deposition

Optical properties of the UO2+x film deposited by a polymer-assisted deposition method have been investigated by spectroscopic ellipsometry (SE). This epitaxial film contains at least two kinds of uranium oxides of U3O8 and UO3, and the O/U ratio is 2.74, which is confirmed by x-ray diffraction (XRD) and scanning Auger microscopy methods. By investigating the optical constants, the bandgaps of U3O8 and UO3 are determined as 2.3 and 1.0 eV, respectively, and 80% of the epitaxial film is U3O8 and 20% is UO3. The speciation signatures from the XRD and band structures show that the UO2+x epitaxial film reduced to U3O8 with the heating treatment at 480 K in a vacuum while oxidized to UO3 at 650 K. This work demonstrates a useful tool for studying the optical properties, band structures, and phase transition of uranium oxide film by SE.

Quantitative material analysis using secondary electron energy spectromicroscopy

This paper demonstrates how secondary electron energy spectroscopy (SEES) performed inside a scanning electron microscope (SEM) can be used to map sample atomic number and acquire bulk valence band density of states (DOS) information at low primary beam voltages. The technique uses an electron energy analyser attachment to detect small changes in the shape of the scattered secondary electron (SE) spectrum and extract out fine structure features from it. Close agreement between experimental and theoretical bulk valance band DOS distributions was obtained for six different test samples, where the normalised root mean square deviation ranged from 2.7 to 6.7%. High accuracy levels of this kind do not appear to have been reported before. The results presented in this paper point towards SEES becoming a quantitative material analysis companion tool for low voltage scanning electron microscopy (LVSEM) and providing new applications for Scanning Auger Microscopy (SAM) instruments.

Sunlight Selective Photodeposition of CoOx(OH)y and NiOx(OH)y on Truncated Bipyramidal BiVO4 for Highly Efficient Photocatalysis.

Facet-engineered monoclinic scheelite BiVO4 particles decorated with various cocatalysts were successfully synthesized by selective sunlight photodeposition of metal or metal oxy(hydroxide) nanoparticles onto the facets of truncated bipyramidal BiVO4 monoclinic crystals coexposing {010} and {110} facets. X-ray photoelectron spectroscopy, scanning electron microscopy, and scanning Auger microscopy revealed that metallic silver (Ag) and cobalt (oxy)hydroxide (CoOx(OH)y) particles were selectively deposited onto the {010} and {110} facets, respectively, regardless of the cocatalyst amount. By contrast, the nickel (oxy)hydroxide (NiOx(OH)y) photodeposition depends on the nickel precursor amount with an unprecedented selectivity for 0.1 wt % NiOx(OH)y/BiVO4 with a preferential deposition onto the {010} facets and the edges between the {110} facets. Moreover, these noble metal-free heterostructures led to remarkable photocatalytic properties for rhodamine B photodecomposition and sacrificial water oxidation reactions. For instance, 0.2 wt % CoOx(OH)y/BiVO4 led to one of the highest oxygen evolution rates, i.e., 1538 μmol h-1 g-1, ever described which is ten times higher than that found for bare BiVO4. The selective deposition of cobalt (oxy)hydroxide species onto the more electron-deficient facet of truncated bipyramidal monoclinic BiVO4 particles favors photogenerated charge carrier separation and therefore plays a key role for efficient photochemical oxygen evolution.

Layer etching of mica nanosheets using a focused electron beam

Mica, a cleavable layered material, is a single-crystalline phyllosilicate having unique electronic and mechanical properties such as a wide bandgap and tolerance to strong electric fields and high temperatures, and is applicable to flexible electronics. This paper describes the nanometer-level layer etching of mica nanosheets exfoliated from artificially synthesized phlogopite and affixed on substrates, using a focused electron beam for fine-pattern fabrication of the nanosheets. The dependence of the etching on the irradiation time, beam current, and beam energy is examined. The etching process was analyzed by in situ scanning Auger electron spectroscopy and microscopy. The layer etching of mica nanosheets leads to the micro- and nano-fabrication of mica-based two-dimensional heterodevices.

The effect of metal-oxide incorporation on the morphology of carbon nanostructures

Metal-organic, single-source, low-temperature, morphology-controlled growth of carbon nanostructures is achieved, using an inductively coupled plasma-enhanced chemical vapor deposition system. Three distinctive morphologies, namely nanoflakes, nanowalls (CNWs) and nanorods (and intermediates between these morphologies), can be reproducibly deposited, depending on the process parameters. The synthesized structures can be described as hybrid materials consisting of metal oxide incorporated in a carbon matrix material. Since the incorporation of metal oxide into the carbon structure significantly influences their growth, the synthesis cannot be described solely with the existing models for the growth of CNWs. Optical emission spectroscopy is used to measure the relative number density of suspected growth and etching species in the plasma, while physical and chemical surface analysis techniques (scanning electron microscopy, Raman spectroscopy, scanning Auger microscopy and x-ray photoelectron spectroscopy) were employed to characterize the properties of the different nanostructures. Therefore, by using methods for both plasma and surface characterization, the growth process can be understood. The precursor dissociation in the plasma can be directly linked to the deposited morphology, as the incorporation of Al2O3 into the nanostructures is found to be a major cause for the transition between morphologies, by changing the dominant type of defect within the carbon structure.

Leaded Bronze Alloy as a Catalyst for the Electroreduction of CO2

AbstractThe performance of a leaded bronze alloy with CuSn7Pb15 (wt %) chemical composition is studied as a cathode material for CO2 electroreduction (CO2RR) in aqueous 0.5 M KHCO3 electrolyte. It was found that the catalytic characteristics of the proposed CO2RR electrocatalyst are dominated by elemental lead. Surface characterization by means of digital 3D optical microscopy, white light interferometry, scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and scanning auger microscopy (SAM) revealed that segregated Pb clusters embedded in a Cu‐rich Cu/Sn matrix are, to a large extent, dispersed on the cathode surface upon sample preparation through mechanical polishing. Identical location SEM‐EDX studies before and after CO2 electrolysis revealed that further Pb surface redistribution takes place under operando CO2RR conditions, provided sufficiently high potentials are applied. The as‐prepared electrocatalyst proved to be a suitable and powerful alternative for the selective and efficient production of formate (maximum achieved faradaic efficiency and partial current density for formate are 58.6 % and −11.08 mA cm−2 at −1.07 V and −1.17 V vs. RHE, respectively). Moreover, in comparison to neat lead, this material can be handled with less precaution.

Scanning Auger Microscopy Studies of Silane Films Grown on Plasma-Modified HOPG Surfaces.

The growth of silane films on plasma oxidized highly oriented pyrolytic graphite (HOPG) surfaces has been studied using wet chemical deposition of propyltrimethoxysilane (PTMS) and propyldimethylmethoxysilane (PDMMS). Scanning Auger microscopy (SAM) and X-ray photoelectron spectroscopy (XPS) were used to investigate the chemical composition and morphology of the silane films. The effects of several deposition parameters were examined, including the necessity of oxidation of the HOPG surface, addition of water with the silane, and rinsing before curing. The optimal conditions needed to create a complete uniform film differ for the two silanes due to differences in their structures. Both silanes require an oxidized HOPG surface for a film to grow, the addition of water with PTMS results in a thicker film, while the addition of water with PDMMS decreases the film growth. Rinsing of both samples before curing removes physisorbed species, leaving only the covalently bonded film on the surface.

Investigation of the Interactions between Electrodes in Li4Ti5O12 – Based Batteries with Complementary Surface Analysis Techniques (XPS, SAM, ToF-SIMS)

Li4Ti5O12(LTO)-based negative electrode for lithium-ion batteries is of interest for electrical vehicles due to its safety, low cost and cycling stability [1]. In this study, the effect of the positive electrode on the electrochemical performances of LTO electrodes, in relation with the Solid Electrolyte Interphase (SEI) properties, has been investigated [2]. Full cells LTO/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO) were cycled at 40°C over 100 cycles and the electrodes were analyzed by XPS, Scanning Auger Microscopy (SAM) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) after one and 100 cycles (figure 1). Moreover, LTO/LTO symmetrical cells were also analyzed in order to be free of the positive electrode impact. For each system, LTO electrodes are homogeneously covered by surface layers since the first cycle which induces an irreversible capacity loss. This latter is more important for LTO/LMO compared to LTO/NMC and LTO/LTO. Both SEI layers are composed of organic (polyethylene oxides, oxalates) and inorganic species (LiF, phosphates and fluorophosphates) but in different proportions and with different 2D and 3D spatial distributions: fluorine species are detected deeper in the electrode than organic species and in higher quantities for LTO/LMO for instance [3]. Moreover, the SEI is thicker on the LTO electrode when cycled versus LMO compared to NMC and contains small amounts of manganese, homogeneously spread over the surface and deeply inserted in the SEI, which entails an increase of the system impedance. In conclusion, a thick SEI associated with the presence of metallic species could alter the passivating role of the SEI and explain the less efficient electrochemical performance of LTO/LMO cells. [1] Tarascon et al. Nature 2001, 414, 359–367. [2] El Ouatani et al. Journal of The Electrochemical Society, 156(6): A468, 2009. [3] Nicolas Gauthier et al. Journal of The Electrochemical Society, 165(13): A2925-A2934, 2018. Figure 1

Review—Laser Ablation Ionization Mass Spectrometry (LIMS) for Analysis of Electrodeposited Cu Interconnects

In this contribution highly sensitive and quantitative analytical methodologies based on femtosecond Laser Ablation Ionization Mass Spectrometry (fs-LIMS) for the analysis of model systems and state-of-the-art Cu interconnects are reviewed and discussed. The method development introduces in a first stage a 1D chemical depth profiling approach on electrodeposited Cu films containing periodically confined organic layers. Optimization of measurement conditions on these test platforms enabled depth profiling investigations with vertical resolution at the nm level. In a second stage, a matrix-free laser desorption methodology was developed that allowed for preliminary molecular identification of the embedded organic contaminants beyond elementary composition. These studies provided specific fragmentation markers in the lower mass range, which support a previously proposed reaction mechanism responsible for successful leveling employing a new class of plating additives for Damascene processes. Further combined LIMS and Scanning Auger Microscopy (SAM) studies on through-silicon-vias (TSV) interconnects confirmed the embedment upon plating of the organic additives at the upper side-walls of the TSV channel in the boundary between the Cu seed layer and the electrodeposited Cu.

Spatially selective reversible charge carrier density tuning in WS2 monolayers via photochlorination

Chlorine-doped tungsten disulfide monolayer (1L-WS2) with tunable charge carrier concentration has been realized by pulsed laser irradiation of the atomically thin lattice in a precursor gas atmosphere. This process gives rise to a systematic shift of the neutral exciton peak towards lower energies, indicating reduction of the crystal’s electron density. The capability to progressively tune the carrier density upon variation of the exposure time is demonstrated; this indicates that the Fermi level shift is directly correlated to the respective electron density modulation due to the chlorine species. Notably, this electron withdrawing process enabled the determination of the trion binding energy of the intrinsic crystal, found to be as low as 20 meV, in accordance to theoretical predictions. At the same time, it is found that the effect can be reversed upon continuous wave laser scanning of the monolayer in air. Scanning auger microscopy (SAM) and x-ray photoelectron spectroscopy (XPS) are used to link the actual charge carrier doping to the different chlorine configurations in the monolayer lattice. The spectroscopic analyses, complemented by density functional theory calculations, reveal that chlorine physisorption is responsible for the carrier density modulation induced by the pulsed laser photochemical reaction process. Such bidirectional control of the Fermi level, coupled with the capability offered by lasers to process at pre-selected locations, can be advantageously used for spatially resolved doping modulation in 1L-WS2 with micrometric resolution. This method can also be extended for the controllable doping of other TMD monolayers.

High energy pulsed laser deposition of ohmic tungsten contacts on silicon at room temperature

Tungsten-on-n+ silicon ohmic contacts were obtained by depositing 100 nm-thick W coatings on silicon substrates using pulsed laser deposition at room temperature, without native oxide removal. The high energy of the impinging species (about 10–100 eV per atom) led to sputtering phenomena and to the implantation of W atoms through the Si oxide. W coatings were characterized, as-deposited and after performing rapid thermal annealing steps. The morphology and crystallinity were characterized by scanning electron microscopy, X-ray diffraction and reflectometry. The interdiffusion of W and Si was shown by scanning Auger microscopy. The ohmic character of the contacts and contact resistance were investigated by the transfer length method. Fast annealing at moderate temperatures (450 °C) remarkably improved contact performance without significant variation of the features of either W film or Si substrates. The ohmic character of the contact was preserved even after annealing at high temperature (1000 °C) at which a complete interdiffusion of Si into the W film takes place.

Compositional, ultrastructural and nanotechnological characterization of the SMA strain of Saccharomyces pastorianus: Towards a more complete fermentation yeast cell analysis.

Nano scanning Auger microscopy (NanoSAM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been used in materials science research for some time, but NanoSAM, in particular, has only recently been applied to biological specimens. Here, the first concurrent utilization of NanoSAM, TOF-SIMS and microscopic techniques for the examination of a standard beverage fermentation strain of Saccharomyces pastorianus uncovered the presence of intracellular networks of CO2 in fermenting cells. Respiring cells produced few bubbles and instead had large internal vacuolar structures. Transmission electron microscopy analysis also showed osmiophilic layers at the cell exterior of fermenting cells that became more prevalent with fermentation duration, while osmiophilic layers were largely absent in respiring cells. TOF-SIMS analysis showed a compositional difference at the exterior and interior of SMA cells and between fermenting and respiring cells. Fermenting cells also appeared to have different 3-OH oxylipin profiles compared to respiring cells based upon examination with immunofluorescence microscopy. The results of this work and further study using these materials science techniques will substantially enhance our understanding of the chemical, ultrastructural and metabolic changes that occur in fermentation yeasts.

Neon isotopes in individual presolar low-density graphite grains from the Orgueil meteorite.

We present He and Ne isotopes of individual presolar graphite grains from a low-density separate from Orgueil. Two grain mounts were analyzed with the same techniques but in a different sequence: The first one was measured with NanoSIMS followed by noble gas mass spectrometry, and the second one in reverse order. No grain contained 4He and only one grain on the second mount contained 3He. On the first mount, the grains had been extensively sputtered with NanoSIMS ion beams prior to noble gas analysis; we found only one grain out of 15 with presolar 22Ne above detection limit. In contrast, we found presolar 22Ne in six out of seven grains on the second mount that was not exposed to an ion beam prior to noble gas analysis. All 22 grains on the two mounts were imaged with scanning electron microscopy (SEM) and/or Auger microscopy. We present evidence that this contrasting observation is most likely due to e-beam-induced heating of the generally smaller grains on the first mount during SEM and Auger imaging, and not primarily due to the NanoSIMS analysis. If thermal contact of the grains to the substrate is absent, such that heat can only be dissipated via radiation, then the smaller, sputter-eroded grains are heated to higher temperatures such that noble gases can diffuse out. We discuss possible gas loss mechanisms and suggest solutions to reduce heating during e-beam analyses by minimizing voltages, beam currents, and dwell times. We also found small amounts of 21Ne in five grains. Using isotope data we determined that the dominant sources of most grains are core-collapse supernovae, congruent with earlier studies of low-density presolar graphite from Murchison. Only two of the grains are most likely from AGB stars, and two others have an ambiguous origin.

Depth Profiling and Cross-Sectional Laser Ablation Ionization Mass Spectrometry Studies of Through-Silicon-Vias.

Through-silicon-via (TSV) technology enables 3D integration of multiple 2D components in advanced microchip architectures. Key in the TSV fabrication is an additive-assisted Cu electroplating process in which the additives employed may get embedded in the TSV body. This incorporation negatively influences the reliability and durability of the Cu interconnects. Here, we present a novel approach toward the chemical analysis of TSVs which is based on femtosecond laser ablation ionization mass spectrometry (fs-LIMS). The conditions for LIMS depth profiling were identified by a systematic variation of the laser pulse energy and the number of laser shots applied. In this contribution, new aspects are addressed related to the analysis of highly heterogeneous specimens having dimensions in the range of the probing beam itself. Particularly challenging were the different chemical and physical properties of which the target specimens were composed. Depth profiling of the TSVs along their main axis (approach 1) revealed a gradient in the carbon (C) content. These differences in the C concentration inside the TSVs could be confirmed and quantified by LIMS analyses of cross-sectionally sliced TSVs (approach 2). Our quantitative analysis revealed a C content that is ∼1.5 times higher at the TSV top surface compared to its bottom. Complementary Scanning Auger Microscopy (SAM) data confirmed a preferential embedment of suppressor additives at the side walls of the TSV. These results demonstrate that the TSV filling concept significantly deviates from common Damascene electroplating processes and will therefore contribute to a more comprehensive, mechanistic understanding of the underlying mechanisms.

Catalyst–substrate interaction and growth delay in vapor–liquid–solid nanowire growth

Understanding of the initial stage of nanowire growth on a bulk substrate is crucial for the rational design of nanowire building blocks in future electronic and optoelectronic devices. Here, we provide in situ scanning electron microscopy and Auger microscopy analysis of the initial stage of Au-catalyzed Ge nanowire growth on different substrates. Real-time microscopy imaging and elementally resolved spectroscopy clearly show that the catalyst dissolves the underlying substrate if held above a certain temperature. If the substrate dissolution is blocked (or in the case of heteroepitaxy) the catalyst needs to be filled with nanowire material from the external supply, which significantly increases the initial growth delay. The experiments presented here reveal the important role of the substrate in metal-catalyzed nanowire growth and pave the way for different growth delay mitigation strategies.

Influence of the Positive Electrode on Li4Ti5O12 (LTO) Electrode/Electrolyte Interfaces in Li-Ion Batteries

Li4Ti5O12(LTO)-based negative electrode for lithium-ion batteries is of interest for electrical vehicles due to its safety, low cost and cycling stability. In this study, the effect of the positive electrode on the electrochemical performances of LTO electrodes, in relation with the Solid Electrolyte Interphase (SEI) properties, has been investigated. Full cells LTO/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO) were cycled at 40°C over 100 cycles and the electrodes were analyzed by XPS and Scanning Auger Microscopy (SAM) after one and 100 cycles. For both systems, LTO electrodes are homogeneously covered by surface layers since the first cycle which induces an irreversible capacity loss. This latter is more important for LTO/LMO compared to LTO/NMC. Both SEI layers are composed of organic (polyethylene oxides, oxalates) and inorganic species (LiF, phosphates and fluorophosphates) but in different proportions: more fluorine species are detected for LTO/LMO for instance. Moreover, the SEI is thicker on the LTO electrode when cycled versus LMO compared to NMC and contains small amounts of manganese, homogeneously spread over the surface. In conclusion, a thick SEI associated with the presence of metallic species could alter the passivating role of the SEI and explain the less efficient electrochemical performance of LTO/LMO cells.

Material and device properties of superacid-treated monolayer molybdenum disulfide

We study the effects of chemical treatment with bis(trifluoromethane) sulfonimide superacid on material and device properties of monolayer molybdenum disulfide grown by chemical vapor deposition. Our spatially resolved photoluminescence (PL) measurements and device studies reveal two key findings due to the chemical treatment: (1) noticeable transformation of trions to neutral excitons, and (2) over 7-fold reduction in the density of mid-gap trap states. Specifically, a combination of scanning Auger microscopy and PL mapping reveals that the superacid treatment is effective in passivating the sulfur-deficient regions.

Influence of Vinylene Carbonate Additive on the Li4Ti5O12 Electrode/Electrolyte Interface for Lithium-Ion Batteries

The effect of Vinylene Carbonate (VC) additive upon the properties of the Solid Electrolyte Interphase (SEI) formed on top of Li4Ti5O12 (LTO) electrodes at 60°C, in relation with electrochemical data has been studied. Half cells LTO/Li were cycled at 60°C with VC-free and VC-containing electrolytes over 30 cycles and electrodes were analyzed by XPS after the first and tenth cycles. Scanning Auger Microscopy (SAM) analysis have also been performed after the first lithiation. XPS results show that for both electrolytes, a SEI is formed during lithiation of LTO electrodes and partially dissolved during delithiation. The use of VC promotes the formation of a thicker SEI since the first cycle, more stable toward dissolution and enhances the amount of organic compounds at the expense of LiF. SAM chemical mappings confirm the formation of a thicker and homogeneously distributed SEI at the first cycle for a VC-containing electrolyte. The dissolution process observed during delithiation mainly involves LiF without VC and Li2CO3 with VC. The formation of a thicker SEI implies higher capacity losses, which is consistent with electrochemical data showing higher capacity losses for a VC-containing electrolyte. VC additive is nonetheless expected to enhance the passivation of LTO electrodes over long cycling.

Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy

Drift correction of the analyzed area during the study of the lateral elemental composition distribution in single semiconductor nanostructures by scanning Auger microscopy