Assessing Oxygen Vacancies in Bismuth Oxide through EELS Measurements and DFT Simulations

Cs-doped hexagonal tungsten bronze (CsxWO3–y) nanoparticles (NPs) constitute an infrared-absorbing material with high visible transparency. In this study, anisotropic dielectric responses of individual NPs were evaluated by employing high-energy-resolution electron energy loss spectroscopy (EELS) operated in the aloof-beam mode. EELS data were obtained by setting an electron nanoprobe just aside NP edges either parallel or perpendicular to the c-axis to realize an anisotropic interaction condition with NPs. In the EELS spectra, peaks were observed at around 1.3 or 0.9 eV, respectively, depending on beam conditions parallel (∥c) or perpendicular (⊥c) to the c-axis. Those peaks dominantly reflected the dielectric tensor components of either ɛzz or ɛxx and evidenced the anisotropic responses of individual NPs. The peak energy in the ∥c condition was larger than that in the ⊥c condition; this finding qualitatively agrees with optical reflection measurements using polarized light. The experimental values of peak energies and widths were, respectively, smaller and larger than the theoretically evaluated values. These differences could be attributed to a damping of dipole oscillation by electronic excitations owing to oxygen vacancies. In addition, the peak energies of ⊥c and ∥c interaction conditions varied in ranges of 0.7–1.0 eV and 1.1–1.6 eV, respectively. Those variation ranges are larger than the measurement error of about 0.1 eV. Such variation in peak energies supports the presence of ensemble inhomogeneity in dielectric responses of NPs. Those results indicate that the anisotropy and inhomogeneity of dielectric response are important factors for understanding the optical properties of nanoparticulate dispersions.

Interaction of oxygen with an alkali modified Ru(001) surface

Cryo-electron microscopy is now an established technique in structural biology for studying vitrified macromolecular assemblies. More recently, there has also been interest in using cryo-electron microscopy combined with electron energy loss spectroscopy (EELS) to determine subcellular water content in cryosections of vitrified tissue. Few EELS measurements have hitherto been obtained from vitrified water or from vitrified aqueous solutions of organic compounds at a resolution better that 1 eV. The purpose of this paper is to establish how valence EELS of vitrified (rapidly frozen) water differs from that of hexagonal (slowly frozen) ice, and also to investigate the effects of electron beam damage on EELS from vitrified aqueous solutions. There is also a fundamental interest in determining the energy loss function to help understand the electronic structure of frozen water, i.e., hexagonal ice, cubic ice and vitreous water, which are strong insulators containing solely hydrogen bonds. Some optical reflectivity measurements have previously been obtained from frozen water in the vacuum ultraviolet up to around 25 eV but it is not clear if these data are accurate over the entire energy range.

We have systematically investigated the localized surface plasmon resonance (LSPR) of the silver nanoparticles by using electron energy loss spectroscopy (EELS) and optical simulation based on boundary element methods with respect to the diameter and the impact parameter variations. The both peaks of EELS and optical curve were occurred from 3.2 to 3.8 eV. Interestingly, we found two types of plasmon modes. At the impact parameter from 0 to R, the plasmon showed the properties as bulk plasmon, while at the greater value than R it showed the surface plasmon mode. This result showed the EELS simulation was better to observe a high-order of LSPR spectra than optical simulation. High-order was originated from a higher multipolar mode and weak interaction in surface plasmon phenomenon. As shown above, the EELS measurement can detect a high-order mode of LSPR than the optical measurement.

Electron energy loss spectroscopy (EELS) is an analytical technique that can provide the structural, physical and chemical information of materials. The EELS spectra can be obtained by combining with TEM at sub-nanometer spatial resolution. However, EELS spectral information can’t be obtained easily because in order to interpret EELS spectra, we need to refer to and/or compare many reference data with each other. And in addition to that, we should consider the different experimental variables used to produce each data. Therefore, reliable and easily interpretable EELS standard reference data are needed.Our Electron Energy Loss Data Center (EELDC) has been designated as National Standard Electron Energy Loss Data Center No. 34 to develop EELS standard reference (SR) data and to play a role in dissemination and diffusion of the SR data to users. EELDC has developed and collected EEL SR data for the materials required by major industries and has a total of 82 EEL SR data. Also, we have created an online platform that provides a one-stop-place to help users interpret quickly EELS spectra and get various spectral information. In this paper, we introduce EEL SR data, the homepage of EELDC and how to use them.

Carbon deposits formed during filament assisted diamond film growth were characterized with x-ray photoelectron spectroscopy (XPS) and electron energy-loss spectroscopy (EELS). The samples were transferred between the growth chamber and the ultrahigh vacuum analytical chamber without exposure to air. These results are presented with an emphasis on data analysis for carbon chemical state identification. By comparison of the C(1s) binding energies to a highly oriented pyrolytic graphite standard, we are able to distinguish pure carbon species, such as diamond and graphite, from compounds, such as SiC and CxHy. For substrates with Z≤30, the loss electrons from the C(1s) core level are free from overlap with the substrate core levels; therefore, EELS spectra can be obtained by x-ray excitation of the C(1s) level. These EELS data can then be used as a fingerprint for distinguishing between diamond, graphite, and carbides. For samples with mixed deposits of diamond and graphite, or carbide and diamond, curve fits of the EELS data can qualitatively determine which species are present.

Analytical investigation of grain boundaries of compressive deformed Al-doped sintered β-SiC

HRTEM(High-Resolution Transmission Electron Microscope), HAADF-STEM (High Angle Annular Dark Field Scanning Transmission Electron Microscope) and EELS(Electron Energy Loss Spectroscopy) techniques were applied for the characterization of Au/TiO2 catalysts. HAADFSTEM provides precise size distributions for Au particles smaller than ∼2nm in diameter. It was observed that many small particles under 2nm were supported on anatase TiO2 having a large surface area. The HAADF-STEM method was examined as a way to measure the shape of Au particles. EELS measurements were also used to examine the interface between Au and TiO2 support to study electronic structure effects.

Introduction Transmission electron energy loss spectroscopy (EELS) consists of measuring energy loss dispersion of inelastically scattered high-energy electrons transmitted through a thin film. The high-energy electrons, which interact with the electrons in the solid, lose a certain amount of energy and transfer momentum to the solid. Because of the energy and momentum conservation rules, energy loss and the corresponding momentum-transfer ( q ) of the probed electron represents the energy and the momentum of the electronic excitations in solids. Although some optical techniques, such as soft X-ray absorption and optical reflectance measurements, provide comparative information about solids with higher energy resolution, EELS enjoys several unique advantages over optical spectroscopies. First of all, unlike optical reflectance measurements which are sensitive to the surface condition of the sample, the transmitted EELS represents the bulk properties of the material. Secondly, EELS spectra can be measured with q along specific controllable directions and thus, can be used to study the dispersion of plasmons, excitons, and other excitations [8.1–8.5]. Such experiments offer both dynamics as well as symmetry information about the electronic excitations in solids. In addition, the capability to probe the electronic structure at finite momentum-transfer also allows one to investigate the excited monopole or quadrupole transitions, which cannot be directly observed by conventional optical techniques limited by the dipole selection rule. Because of the significant energy spread of conventional TEM electron sources (e.g. LaB 6 , W-hairpin filaments with Δ E ∼ 1–2 eV), EELS measurements to investigate the electronic structure of solids have been generally limited to dedicated electron energy loss spectrometers with energy resolutions ∼0.1 eV.

The fundamental knowledge of the interaction between biomolecules and mineral surfaces is of utmost importance to drive new technological advancements, particularly for condensation, aggregation, catalysis and exchange of biomolecules. The mineral surface can be used in several fields and applications, for instance in biotechnology, environmental science and remediation, soil science, agro-food and related technology. This kind of knowledge may also provide several suggestions and have implications also for the prebiotic chemistry field, namely the study of the abiotic physicochemical steps that could have led to the 'creation' of the first known living organism. Nowadays, this kind of information at the micro and nanometric scale can be explored with several experimental and theoretical techniques and, among them, atomic force microscopy (AFM)-related methods and density functional theory (DFT) are particularly suited to investigate adsorption processes at single molecule level. In the present work, the specific interaction at the atomic scale between a small peptide (di-glycine) and the (001) surface of clinochlore, a mineral presenting alternately stacked talc-like layers (hydrophilic) and brucite-like sheets (hydrophobic), was characterized by means of a cross-correlated approach combining AFM and DFT simulations. The experiments evidenced the preferential adsorption of di-glycine onto the hydrophobic brucite-like sheet of the mineral, with the observed molecules organized as dot-like (single-molecules), agglomerates, filament-like and network structures by the surface, whereas only very few peptides were imaged onto the hydrophilic talc-like layer. From the theoretical analysis, the most stable conformation of the di-glycine peptide adsorbed on the mineral surface was calculated, and the binding energy analysis of the specific interaction of the molecule, depending on the local chemistry of the substrate, provided fundamental information to interpret end explain the experimental evidence. LAY DESCRIPTION: The present work aims at extending the knowledge of the biomolecules/minerals interaction world. The fundamental knowledge of the interaction between biomolecules and mineral surfaces is of utmost importance to drive the development of new technological advancements, particularly for condensation, aggregation, catalysis and exchange of biomolecules. The mineral surface can be used as substrate in several fields and applications, for instance in biotechnology, environmental science and remediation, soil science, agro-food and related technology. This kind of research may also provide several suggestions and have implications also for the prebiotic chemistry field, namely the study of the abiotic physicochemical steps that could have led to the "creation" of the first known living organism. Nowadays, this kind of research at the micro and nanometric scale can be performed with several experimental techniques and, among them, scanning probe microscopy-related methods are particularly suited to investigate surface adsorption processes at single molecule level. In the present work, the focus is on the specific interaction at the atomic scale between a small peptide (di-glycine) and the surface of clinochlore (a diffuse clay mineral). Clinochlore is a mineral belonging to the phyllosilicate, formed by alternately stacked hydrophilic talc-like layers [chemical formula Mg3 Si4 O10 (OH)2 ] and hydrophobic brucite-like sheets [magnesium hydroxide, Mg(OH)2 ]. Since these two kind of layered structures are held together by weak (van der Waals) forces, the mineral can be easily cleaved along the [001] crystallographic direction (the stacking direction) and the resulting (001) clinochlore surface may presents at the nanoscale some remainders of one layer (brucite-like or talc-like) on the other. This means that this mineral exposes to the environment two different type of surfaces, one hydrophilic and one hydrophobic, which can selectively interact with (adsorb) different type of molecules at the nanoscale. Clinochlore is also one of the 420 mineral species that were likely present on Earth at the time of life's origins, thus it could have played a fundamental role in prebiotic chemistry. In this study, the interaction between di-glycine and clinochlore was characterized by means of both atomic force microscopy (AFM) at the nanometric scale and density functional theory (DFT) simulations, correlating the results of the two methods (cross-correlation approach). The experiments evidenced the preferential adsorption of di-glycine onto the hydrophobic brucite-like sheet of the mineral, with the observed molecules organized as dot-like (single-molecules) structures, agglomerates, filaments and networks by the surface, whereas only very few peptides were imaged onto the hydrophilic talc-like layer. From the theoretical analysis, the most stable conformation of the di-glycine adsorbed on the mineral surface was calculated, and the binding energy analysis of the specific interaction of the molecule, depending on the local chemistry of the substrate, provided fundamental information to interpret end explain the experimental evidence.

Degradation of caffeic acid by dielectric barrier discharge plasma combined with Ce doped CoOOH catalyst

Understanding the mechanical properties of metal–organic frameworks (MOFs) is essential to the fundamental advancement and practical implementations of porous materials. Recent computational and experimental efforts have revealed correlations between mechanical properties and pore size, topology, and defect density. These results demonstrate the important role of the organic linker in the response of these materials to physical stresses. However, the impact of the coordination bond between the inorganic node and organic linker on the mechanical stability of MOFs has not been thoroughly studied. Here, we isolate the role of this node–linker coordination bond to systematically study the effect it plays in the compression of a series of isostructural MOFs, M-UiO-66 (M = Zr, Hf, or Ce). The bulk modulus (i.e. the resistance to compression under hydrostatic pressure) of each MOF is determined by in situ diamond anvil cell (DAC) powder X-ray diffraction measurements and density functional theory (DFT) simulations. These experiments reveal distinctive behavior of Ce-UiO-66 in response to pressures under one GPa. In situ DAC Raman spectroscopy and DFT calculations support the observed differences in compressibility between Zr-UiO-66 and the Ce- analogue. Monitoring changes in bond lengths as a function of pressure through DFT simulations provides a clear picture of those which shorten more drastically under pressure and those which resist compression. This study demonstrates that changes to the node–linker bond can have significant ramifications on the mechanical properties of MOFs.

Tungsten carbide (WC) is an established model electrocatalyst for the hydrogen evolution reaction (HER) in aqueous solutions. In spite of extensive interest in and work on this material, a systematic atomistic understanding of the combined role of faceting and heteroatom doping for hydrogen evolution on WC electrocatalysts in aqueous solution is not available. To fill this knowledge gap, here we explore the interplay of these parameters for the electrocatalytic performance of WC by means of density functional theory (DFT) simulations. In our simulations, we explicitly account for solvent (water) effects and related electrochemical potential-dependent oxygen or hydroxyl (co)adsorption on the WC surfaces as determined by the analysis of surface Pourbaix diagrams. Among the several low-index WC surfaces screened, the DFT simulations indicate that the W-terminated (−100) and (111) surfaces of WC show comparable exchange currents of 3.908 and 0.133 mA/cm2, respectively. The simulations also suggest that V or N doping can substantially increase the HER activity of some WC surfaces to levels comparable to commercial Pt/C electrocatalysts, with current densities as large as 10.555, 1.730, and 0.636 mA/cm2 for the V-doped W-terminated (001), V-doped (101), and N-doped (101) WC surfaces, respectively. The improved HER activities are rationalized in terms of the d-band or p-band center, which are both shown to be related to the capability of tuning the hydrogen adsorption, and thence the HER performance. The calculated strong dependence of the HER activity on the presence of the electrochemical adsorption of oxygen and hydroxyls reiterates the importance of modeling realistic electrochemical conditions for WC pristine or doped surfaces. We expect the DFT results presented to provide timely and original guidelines for further theoretical and experimental studies of HER activity on WC-related electrocatalysts.

Exploring phononic properties of two-dimensional materials using machine learning interatomic potentials

Both the formation of self-formed barrier (SFB) of Mn oxide on porous low dielectric constant (low-k) SiOCH trench and Cu filling (MOCVD) in order were carried out by in-situ metal organic chemical vapor deposition to make Cu interconnect. Oxygen-plasma pretreatment of the low-k dielectrics surface enhanced the uniformity of deposited Mn layers as well as the formation of SFB prior to Cu MOCVD. X-ray photoelectron spectroscopy confirmed the presence of amorphous MnOx and MnSi(y)Oz layers in SFB. Electron energy loss spectroscopy (EELS) measurements of cross-sectional samples of the deposited layers on porous low-k blanket and trench surfaces enabled in-depth analysis of the elemental composition of the Cu/SFB multilayers with high spatial resolution. The effectiveness of the SFB layer in protecting Cu diffusion into the low-k layer was proven by EELS and energy dispersive X-ray spectroscopy (EDX) analyses. The Mn L3/L2 intensity ratio from EELS data enabled us to identify the possible compounds of the SFB layers including MnSiO3 near the dielectric surface, Mn2O3 near the Cu layer, and Mn3O4 at the intermediate region.