Low Miller Index Research Articles

Crystallographic Dependence of Field Evaporation Energy Barrier in Metals Using Field Evaporation Energy Loss Spectroscopy Mapping.

Atom probe tomography data are composed of a list of coordinates of the reconstructed atoms in the probed volume. The elemental identity of each atom is derived from time-of-flight mass spectrometry, with no local chemical information readily available. In this study, we use a data processing technique referred to as field evaporation energy loss spectroscopy (FEELS), which analyzes the tails of mass peaks. FEELS was used to extract critical energetic parameters that are related to the activation energy for atoms to escape from the surface under intense electrostatic field and dependent of the path followed by the departing atoms. We focused our study on pure face-centered cubic metals. We demonstrate that the energetic parameters can be mapped in two-dimensional with nanometric resolution. A dependence on the considered crystallographic planes is observed, with sets of planes of low Miller indices showing a lower sensitivity to the field. The temperature is also an important parameter in particular for aluminum, which we attribute to an energetic transition between two paths of field evaporation between 25 and 60 K close to (002) pole. This paper shows that the information that can be retrieved from the measured energy loss of surface atoms is important both experimentally and theoretically.

Tuning the adsorption of H2O, H2 and O2 molecules on diamond surfaces by B-doping

In this study, the fundamental interactions between the low Miller index (001), (110) and (111) B-doped diamond surfaces and H2O, H2 and O2 molecules, which are commonly present during growth, in ambient air and involved in electrochemical reactions, are investigated by means of ab initio simulations. The results are presented in close comparison with previous studies on undoped diamond surfaces to reveal the impact of B doping. It is demonstrated that the B dopant is preferably incorporated on the topmost carbon layer and enhances the adsorption of H2O by forming a dative bond with O. On the contrary in some cases, it seems to weaken the adsorption of O2, compared to the undoped diamond. Moreover, a noticeable displacement of the surface atoms attached to the fragment of the dissociated H2O and O2 molecules was observed, which can be associated to early stages of wear at the atomistic level. B doping was also found to reduce the energy barriers for water dissociation in most cases, with this effect being most pronounced in the C(111) surfaces. These qualitative and quantitative results aim to provide useful insights for the development of improved protective coatings and electrochemical devices.

Automated analysis of surface facets: the example of cesium telluride

High-throughput screening combined with ab initio calculations is a powerful tool to explore technologically relevant materials characterized by complex configurational spaces. Despite the impressive developments achieved in this field in the last few years, most studies still focus on bulk materials, although the relevant processes for energy conversion, production, and storage occur on surfaces. Herein, we present an automatized computational scheme that is capable of calculating surface properties in inorganic crystals from first principles in a high-throughput fashion. After introducing the method and its implementation, we showcase its applicability, focusing on four polymorphs of Cs2Te, an established photocathode material for particle accelerators, considering slabs with low Miller indices and different terminations. This analysis gives insight into how the surface composition, accessible through the proposed high-throughput screening method, impacts the electronic properties and, ultimately, the photoemission performance. The developed scheme offers new opportunities for automated computational studies beyond bulk materials.

Dynamic formation of preferentially lattice oriented, self trapped hydrogen clusters

A series of MD and DFT simulations were performed to investigate hydrogen self-clustering and retention in tungsten. Using a newly develop machine learned interatomic potential, spontaneous formation of hydrogen platelets was observed after implanting low-energy hydrogen into tungsten at high fluxes and temperatures. The platelets formed along low miller index orientations and neighboring tetrahedral and octahedral sites and could grow to over 50 atoms in size. High temperatures above 600 K and high hydrogen concentrations were needed to observe significant platelet formation. A critical platelet size of six hydrogen atoms was needed for long term stability. Platelets smaller than this were found to be thermally unstable within a few nanoseconds. To verify these observations, characteristic platelets from the MD simulations were simulated using large-scale DFT. DFT corroborated the MD results in that large platelets were also found to be dynamically stable for five or more hydrogen atoms. The LDOS from the DFT simulated platelets indicated that hydrogen atoms, particularly at the periphery of the platelet, were found to be at least as stable as hydrogen atoms in bulk tungsten. In addition, electrons were found to be localized around hydrogen atoms in the platelet itself and that hydrogen atoms up to 4.2 Å away within the platelet were found to share charge suggesting that the hydrogen atoms are interacting across longer distances than previously suggested. These results reveal a self-clustering mechanisms for hydrogen within tungsten in the absence of radiation induced or microstructural defects that could be a precursor to blistering and potentially explain the experimentally observed high hydrogen retention particularly in the near surface region.

Exploring the Redox Properties of the Low-Miller Index Surfaces of Copper Tungstate (CuWO4): Evaluating the Impact of the Environmental Conditions on the Water Splitting and Carbon Dioxide Reduction Processes.

Photocatalysis has gained significant attention and interest as an environmentally friendly and sustainable approach to the production of hydrogen through water splitting and the reduction and conversion of CO2. Copper tungstate (CuWO4) is a highly promising candidate for these applications owing to its appropriate bandgap and superior stability under different conditions. However, the redox behavior of the CuWO4 surfaces under different environments and their impact on the morphology of the material nanoparticles, as well as the electronic properties, remain poorly understood. In this study, we have employed density functional theory calculations to investigate the properties of the bulk and pristine surfaces of CuWO4 and how the latter are impacted by oxygen chemisorption under the conditions required for photocatalytic water splitting and carbon dioxide reduction processes. We have calculated the lattice parameters and electronic properties of the bulk phase, as well as the surface energies of all possible nonpolar, stoichiometric, and symmetric terminations of the seven low-Miller index surfaces and found that the (010) and (110) facets are the thermodynamically most stable. The surface-phase diagrams were used to derive the equilibrium crystal morphologies, which show that the pristine (010) surface is prominent under synthesis and room conditions. Our crystal morphologies suggest that the partially oxidized (110) surface and the partially reduced (011) surface may play an important role in the photocatalytic splitting of water and CO2 conversion, respectively. Our results provide a comprehensive understanding of the CuWO4 surfaces under the conditions of important photocatalytic applications.

Analysis of surface stability of ferrocolumbite from combined DFT – Wulff construction simulations

Ferrocolumbite, a variegated oxide mineral bearing the strategic element niobium, exhibits an array of surface chemical compositions across various cleavage orientations. The complexity of Nb-bearing ores hinders the efficiency of separation processes, necessitating fundamental research to bridge the knowledge gap regarding the surface dominance and properties of the mineral. In this regard, density functional theory (DFT) simulations were performed to determine the stability of different low Miller index surfaces of ferrocolumbite. The thermodynamic Wulff construction theory was then employed to predict the morphology of a ferrocolumbite nanoparticle, taking into account the DFT-calculated surface energies and the symmetries in the ferrocolumbite crystal. Several descriptors, such as ionic atom density and bond length distribution, were partially successful in correlating with surface energies; however, no global correlation could be captured for this complex system. Our findings suggested oxygen-terminated surfaces generally exhibit greater stability than metal or mixed-metal–oxygen-terminated surfaces within a given facet. Based on the Wulff shape prediction, the {110}, {001}, {111}, and {021} facets contribute to >85% of the surface area of the ferrocolumbite particles after comminution. Therefore, a sound conclusion about the adsorption behavior of reagents on ferrocolumbite should include all of these facets. This fundamental research highlights the complex and diverse nature of the ferrocolumbite surface and paves the way for future investigations.

Electronic structure, work function and band alignment of low Miller-index β-TaON surfaces; a DFT + U study

First principles calculations using GGA + U method have been carried out to study the stability, electronic structure, work function, and band alignment of low Miller-index surfaces of β-TaON. Fifteen possible surface terminations are included in this study. We found that, among all these surfaces, the O-terminated (111) has the lowest surface energy under all growth conditions followed by the O-terminated (100), the (110) and the (101) surfaces, respectively. The calculated band gap values for these surfaces are; 2.30, 2.20, 2.39 and 2.35 eV, respectively. Based on the determined band edges positions and taking into account the effect of surface states, we found that the (111)_O and (011)_O surfaces are appropriate for photo-catalytic splitting of water while the (100)_O and (101) surfaces are only appropriate for oxygen evolution reaction (OER). Furthermore, our results show that the (110) and (011)_TaN surfaces are suitable for hydrogen evolution reaction only. Our results show also that the electron affinity and work function of TaON depend greatly on the nature of surface termination.

Evolution hydrothermal aging resistance mechanism study of zirconium and manganese doped CeO2 catalysts in soot catalytic combustion based on low Miller indices crystal surface effect

The thermogravimetric analysis (TGA) experiments were carried out to reveal the mechanism of Zr and Mn doping on catalytic activity of CeO2 catalyst both fresh and after hydrothermal aging, and the lattice morphology and valence changes were characterized by means of Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR). Density functional theory (DFT) and molecular thermodynamics calculations were applied to investigate the change in catalytic activity, crystal surface energy and crystal morphology caused by hydrothermal aging. The maximum reaction rate temperature of fresh Mn/CeO2 (389 °C) is similar to that of CeO2 (371 °C) and lower than that of Zr/CeO2 (447 °C), but the catalytic performance of CeO2 decreases more severely after hydrothermal aging. The catalyst crystals show different degrees of crystal surface migration after hydrothermal aging, which leads to the reduction of Ce3+/Ce4+ ratio and the active sites shift. DFT calculations indicate that the doping of Zr and Mn reduces the surface energy of the low Miller indices surface and increases the oxygen vacancy formation energy, leading to better thermal stability and lower catalytic activity. The Zr and Mn doping also changes the adsorption energy and Gibbs free energy of H2O, which dominates the migration of (1 1 1) to (1 1 0) and (1 0 0) in the vapor environment. The crystal surface migration mechanism of CeO2 catalysts doped with Zr and Mn induced by H2O molecules at high temperature obtained in this study can provide a valuable addition to the regeneration of CeO2 catalysts in the after-treatment systems of diesel engines.

Effect of faceting on olivine wetting properties

Abstract Grain-scale pore geometry primarily controls the fluid distribution in rocks, affecting material transport and geophysical response. The dihedral angle (θ) in the olivine-fluid system is a key parameter determining pore fluid geometry in mantle wedges. In the system, curved and faceted olivine-fluid interfaces define θ, resulting in faceted-faceted (FF), faceted-curved (FC), and curved-curved (CC) angles. The effect of faceting on θ under various pressure and temperature (P-T) conditions and fluid compositions, however, has not been constrained, and mineralogical understanding remains unresolved. This study evaluated facet-bearing θ and their proportions in olivine-multicomponent aqueous fluid systems. Our results show that 1/3 of olivine-fluid θ are facet-bearing angles, regardless of the P-T conditions and fluid composition. Faceting produces larger dihedral angles than CC angles. The grain boundary plane (GBP) distribution reveals that the GBPs of faceted interfaces at triple junctions have low Miller index faces ({100}, {010}, and {101}). The misorientation angle/axis distributions of adjacent grain pairs are in accord with a theoretical distribution of random olivine aggregate. Moreover, the calculation of the FF angles for adjacent grain pairs with low Miller index GBPs reproduces measured angle values based on the olivine crystal habit. Therefore, our study suggests that the FF angle is strongly affected by olivine crystallography. The presence of faceting increases θ and a critical fluid fraction (φc) for percolation, lowering permeability. In the mantle wedge, where olivine crystallographic preferred orientation (CPO) is expected owing to corner flow, increasing the FF angle proportion with associated changes in fluid pore morphology will lead to permeability anisotropy, and controlling the direction of the fluid flow, and it will result in geophysical anomalies such as seismic wave attenuation and high electrical conductivity.

Evolution hydrothermal aging mechanism for Ag/CeO2 catalysts in regeneration of catalytic diesel particulate filter with DFT calculation.

In order to avoid the high cost of existing precious metal catalyst like Pt, Ag/CeO2 was the most promising catalysts for mobile source soot emission control technologies, but there was a clear trade-off between hydrothermal aging resistance and catalytic oxidation performance hindered the application of this catalyst. In order to reveal the hydrothermal aging mechanism of Ag/CeO2 catalysts, the TGA (thermogravimetric analysis) experiments were investigated to reveal the mechanism of Ag modification on catalytic activity of CeO2 catalyst between fresh and hydrothermal aging and were also characterized with the related characterization experiments to in-depth research the lattice morphology and valence changes. The degradation mechanism of Ag/CeO2 catalysts in vapor with high-temperature was also explained and demonstrated based on density functional and molecular thermodynamics theories. The experimental and simulation data showed that the catalytic activity of soot combustion within Ag/CeO2 decreased more significantly after hydrothermal aging than CeO2 due to the less agglomerated, which caused by the decreased in OII/OI and Ce3+/Ce4+ compared with CeO2. As shown in density function theory (DFT) calculation, the decreased surface energy and the increased oxygen vacancy formation energy of the low Mille index surface after Ag modification led to the instability structure and the high catalytic activity. Ag modification also increased the adsorption energy and Gibbs free energy of H2O on the low Miller index surface compared to CeO2, indicating that the desorption temperature of H2O molecules in (1 1 0) and (1 0 0) was higher than (1 1 1) in CeO2 and Ag/CeO2, which led to the migration of (1 1 1) crystal surfaces to (1 1 0) and (1 0 0) in the vapor environment. These conclusions can provide a valuable addition to the regenerative application of Ce-based catalysts in diesel exhaust aftertreatment system the aerial pollution.

A computational map of the probe CO molecule adsorption and dissociation on transition metal low Miller indices surfaces

The adsorption and dissociation of carbon monoxide (CO) have been studied on 81 Transition Metal (TM) surfaces, with TMs having body centred cubic (bcc), face centred cubic (fcc), or hexagonal close-packed (hcp) crystalline structures. For each surface, CO, C, and O adsorptions, and C+O co-adsorptions were studied by density functional theory calculations on suited slab models, using the Perdew-Burke-Ernzerhof functional with Grimme’s D3 correction for dispersive forces. CO dissociation activation and reaction energies, ΔE, were determined. The values, including zero point energy, were used to capture chemical trends along groups, d-series, and crystallographic phases concerning CO adsorption and dissociation, while simulated infrared (IR) spectroscopies and thermodynamic phase diagrams are provided. Late fcc TMs are found to adsorb CO weakly, perpendicularly, and are IR-visible, opposite to early bcc TMs, while hcp cases are distributed along these two extremes. The d-band centre, εd, is found to be the best descriptor for CO adsorptions and C + O co-adsorptions, ΔE, and activation energies. The implications of the found trends and descriptors are discussed on processes requiring CO dissociation, such as the Fischer-Tropsch.

Electronically Nonadiabatic H Atom Scattering from Low Miller Index Surfaces of Silver.

The reactivity of a surface depends strongly on the surface structure. To study the influence of surface structure on H atom adsorption, we performed inelastic scattering experiments and complementary electronically nonadiabatic molecular dynamics (MD) simulations for H atoms colliding with the three low Miller index surface facets of silver. Experiment reveals very similar energy loss distributions for all three investigated facets. However, for the (100) facet a dependence on the surface orientation is observed that is absent for the other two facets. The nonadiabatic MD simulations manage to describe the experiments well. Despite the observed insignificant influence of the surface geometry on the energy loss distributions, our simulations predict that the capability of the H atoms to penetrate the surface critically depends on the surface structure. The observed crystal orientation dependence of the energy loss distributions in the experiment for Ag(100) cannot be explained with our simulations, and we provide a discussion for a better theoretical description of this system to stimulate future computational investigations.

Density functional theory investigations into the magnetic ordering of U3O8

Density functional theory (DFT) has been highly successful in supporting experimental materials science; however, a correct electronic ground state is required to realize the full theoretical capacity of DFT. The uranium oxides, $\ensuremath{\alpha}\ensuremath{-}{\mathrm{U}}_{3}{\mathrm{O}}_{8}$ in particular, are simultaneously technologically important materials and theoretically challenging for DFT because the uranium magnetic ground state is not obvious. This is true for both experiment and theory---magnetic susceptibility measurements indicate an antiferromagnetic (AFM) ground state with transitions near 4.2 and 8.0 K, but the ordering itself is not known. Theoretical literature reports are in contradiction, with independent studies finding paramagnetic, ferromagnetic (FM), and AFM states as the lowest energy configuration. However, recent inelastic neutron scattering experiments suggested an uninvestigated magnetic structure with ordering along the [0.5 1 1] plane, motivating a theoretical reinvestigation. Using this insight, we calculated the relative energy of FM and AFM orderings along [0.5 1 1], [0.5 0 0], [0 1 0], and [0 0 1] using noncollinear DFT calculations with spin-orbital coupling. We found that the [0.5 1 1] AFM structure is lower in energy than FM or AFM orderings along the low Miller index directions. We also investigated polarization of the magnetic moment along each lattice vector and found that polarization along the out-of-plane direction is the energetically preferred orientation for the AFM structures. Additionally, we found in all calculations that moments initially pointing along the in-plane lattice vectors significantly relax until they point along the coordinate between the two crystallographically distinct uranium sites with complex noncollinear magnetic configurations. The new [0.5 1 1] AFM magnetic structure provides an additional path forward toward understanding the electronic structure of \ensuremath{\alpha}-${\mathrm{U}}_{3}{\mathrm{O}}_{8}$ and lends theoretical credibility to recent neutron scattering results.

Understanding the electrochemical hydrogenation of acetone on Pt single crystal electrodes

• Pt(1 1 0) electrode is the only basal plane active for the acetone electroreduction. • The inclusion of (1 1 1) steps on (1 1 0) terraces slightly alters the behavior of Pt(1 1 0). • Insertion of (1 0 0) steps on (1 1 0) terraces decreases the activity. • Sulfate competes with acetone for the surface sites. The heterogeneous upgrading of biomass by means of electrocatalytic hydrogenation is an attractive way to refine products for industrial and pharmaceutical purposes. Also, the efficient electrochemical reduction of carbonyl compounds can act as hydrogen vectors, and therefore energy vectors. In this manuscript, we render further fundamental insights into the electrochemical reduction of acetone as a model molecule of carbonyl compounds. The structural sensitivity of the reaction is demonstrated by using platinum single crystal electrodes with low Miller indices and stepped electrodes with (1 1 0) terraces and either (1 1 1) or (1 0 0) monoatomic steps. Among the basal planes, Pt(1 1 0) is the only one active for the electroreduction of acetone. The inclusion of (1 1 1) steps on the (1 1 0) terraces does not significantly alter the behavior of Pt(1 1 0), but increasing the (1 0 0) step density has been observed to decrease the activity. We attribute this different performance to a geometrical effect of the active sites. By using different supporting electrolytes, we have found that sulfate competes with acetone for the surface sites, thus modifying the adlayer interfacial structure and hampering acetone reactivity.

Adsorption of the prototypical organic corrosion inhibitor benzotriazole on the Cu(100) surface

The interaction of benzotriazole (BTAH) with Cu(100) has been studied as a function of BTAH exposure in a joint experimental and theoretical effort. Scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), high resolution electron energy loss spectroscopy (HREELS) and density functional theory (DFT) calculations have been combined to elucidate the structural and chemical characteristics of this system. BTAH is found to deprotonate upon adsorption on the copper surface and to adopt an orientation that depends on the molecular coverage. Benzotriazolate (BTA) species initially lie with their planes parallel to the substrate but, at a higher molecular coverage, a transition occurs to an upright adsorption geometry. Upon increasing the BTAH exposure, different phases of vertically aligned BTAs are observed with increasing molecular densities until a final, self-limiting monolayer is developed. Both theory and experiment agree in identifying CuBTA and Cu(BTA)2 metal-organic complexes as the fundamental building blocks of this monolayer. This work shows several similarities with the results of previous studies on the interaction of benzotriazole with other low Miller index copper surfaces, thereby ideally completing and concluding them. The overall emerging picture constitutes an important starting point for understanding the mechanism for protection of copper from corrosion.

Insight into the elemental mercury immobilization mechanism with carbon and sulfur over the mackinawite (FeS) surface via density functional theory

Elemental mercury (Hg0) adsorption behaviors and mechanisms on the low-Miller index mackinawite surface (FeS(001)-S surface), with the engagement of carbon or sulfur, were investigated via DFT-D2 theoretical calculations. The simulation results show that the most favorable adsorption site for the C and Hg atoms was the lower-S site on the pristine surface, while S atom preferred the upper-S site. C atom could cause charge transfer and inter-atomic charge redistribution during adsorption. The carbon atom performs as a linker to connect the substrate and the Hg atom in the most stable mercury adsorption geometry onto the carbon-doped surface. Hg0 is physically adsorbed over the sulfur-doped surface. The HgS molecule chemically attached to the surface at the upper-S site via the Hg atom to form a S-Hg-S structure, and its generation process follows Langmuir-Hinshelwood Mechanism. Firstly, the Hg and S atoms were pre-adsorbed on the FeS(001)-S surface. Then the system needed to overcome an activation energy barrier (Eb) of 89.82 kJ·mol−1. It was an endothermic process in which two separate atoms generated HgS*. However, C atom will impede the reaction as occupying the adsorption sites of mercury and sulfur.

Density functional theory study of CH4 dissociation and C[sbnd]C coupling on W-terminated WC(0001) surface

To explore the catalytic activity of tungsten monocarbide (WC), the methane (CH4) dehydrogenation and further CC coupling process on WC surface have been studied systematically by performing density functional theory (DFT) calculations. The scaling relationship of the adsorption energies of CHx intermediates on W-terminated WC(0001) surface has been summarized together with those cases on pure metal surfaces. By the way, we also studied the thermal stabilities of low Miller index surfaces of WC to obtain the Wulff construction of WC nanocrystal. The W-terminated WC(0001), W-terminated WC(112̄1), and WC-terminated WC(112̄0) facets constitute more than 96% of the total exposed surface in the WC Wulff construction. The van der Waals (vdW) interaction between adsorbate and W-terminated WC(0001) surface is corrected by the BEEF-vdW functional. Our calculations show that W-terminated WC(0001) surface is the most favorably exposed surface with a lower surface energy. Based on the data collected from literature, the linear relationship between the CHx adsorption energies and the x in CHx on metal (e.g., Fe, Co, Ni, Cu, Pt, Ir, Rh, Ru, Pd, Ag, and Au) surfaces has been analyzed. More interestingly, we found that the Co(111), Ni(111), and W-terminated WC(0001) surfaces possess very close slope factors in such a linear relationship, suggesting the similar catalytic property of methane dehydrogenation on these surfaces. More importantly, the rate-limiting step of CH4 dissociation on W-terminated WC(0001) surface corresponds to CH∗→ C∗+H∗. The energy barrier [i.e., 1.46 eV (1.63 eV) with (without) zero point energy (ZPE) correction] for this reaction step is slightly larger than the one on Ni(111) surface and smaller than the one on Cu(111) surface. Furthermore, we have studied the CC coupling through the CH∗ intermediates on W-terminated WC(0001) surface and found that the formation of C2H2 is kinetically favorable. Our results provides useful information for the development of tungsten-carbide-based catalyst materials.

On the growth of functionally graded self-lubricating layer during a plasma-assisted thermochemical treatment of M50NiL steel

Diamond-like carbon (DLC) with excellent mechanical properties has aroused great interest. However, the weak adhesion between the DLC film and steel substrate restricts its application. Considering that the addition of interlayers needs cumbersome steps, fabricating a functionally graded self-lubricating layer through one-step remains a challenge. We reported a novel integrated self-lubricating layer, inspired by the gradient structure formed during the traditional thermochemical treatment. That integrated layer from DLC structure gradual transition to nitrided diffusion layer is in-situ fabricated on the M50NiL steel through a plasma-assisted thermochemical treatment. The gradient structure possesses excellent wear resistance due to the self-lubricating of the DLC structure and provides sufficient adhesion strength. A deep insight into the relation between Fe5C2 crystal facet and growth of DLC is conducted by first-principle calculation and find low Miller Index of Fe5C2 facets are favorable for the growth of DLC. The thermodynamic calculation reveals that gradient structure formation is the collaboration effect of non-equilibrium and equilibrium processes.

Anisotropies of angle-resolved polarized Raman response identifying in low miller index β-Ga2O3 single crystal

Beta-phase gallium oxide (β-Ga2O3) with a monoclinic lattice structure is a research hotspot in the field of ultra-wide bandgap semiconductors in the world and displays intriguing anisotropic properties. Here, we synthesize β-Ga2O3 single-crystal (SC) using the edge-defined film-fed growth method and systematically investigate the anisotropic structural and vibrational properties. The anisotropic nature of β-Ga2O3 SC is revealed by angle-resolved polarized Raman spectroscopy under linearly polarized excitations, in which different vibration modes exhibit pronounced periodic variations in intensity. In the detection of different excitation wavelengths, not only the Raman intensity show significant change, but also the strongest main peak of the Raman modes also shows significant difference. In addition, the angular dependence of the peak intensities of the Ag(4), Ag(6), Ag(7), Ag(10) and Bg modes will also be affected by different low Miller index. All the experimental results above are beneficial to the understanding of inelastic light-scattering process of β-Ga2O3 SC.

Computational study of bulk and surface properties on ruthenium oxide (RuO2)

Metal oxides are widely used in lithium-air batteries to improve the formation of stable discharge products and improve lifespan and electrochemical performance. Despite the intense studies on metal oxides catalysts, ruthenium oxide attracted the most attention since it doesn’t only catalyse the redox processes but reduces the over-potential and stabilizes the Li cyclability. Hence, in this work we discuss the bulk and low Miler index surfaces of RuO2 using the first principle density functional theory calculations. It was found that the lattice parameters are in good agreement with the reported results, with less than 1.4% difference. Furthermore, RuO2 was also found to be mechanically stable with all positive independent elastic constants (Cij) obeying the mechanical stability criteria and a positive tetragonal shear modulus (C’> 0). The bulk to shear ratio indicates that the structure is ductile. The density of states shows a slight pseudo gap for RuO2 at the Fermi energy, which suggests that the structure is stable. Finally, low Miller index surfaces (i.e. (110), (010), (001), (111), and (101)) were modelled using METADISE code, and the most stable facet was in agreement with the reported literature.