Electronic Structure of the Metastable Epitaxial Rock-Salt SnSe { 111 } Topological Crystalline Insulator
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
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Epitaxial growth and electronic structure of oxyhydride SrVO{sub 2}H thin films
Oxyhydride SrVO{sub 2}H epitaxial thin films were fabricated on SrTiO{sub 3} substrates via topotactic hydridation of oxide SrVO{sub 3} films using CaH{sub 2}. Structural and composition analyses suggested that the SrVO{sub 2}H film possessed one-dimensionally ordered V-H{sup −}-V bonds along the out-of-plane direction. The synthesis temperature could be lowered by reducing the film thickness, and the SrVO{sub 2}H film was reversible to SrVO{sub 3} by oxidation through annealing in air. Photoemission and X-ray absorption spectroscopy measurements revealed the V{sup 3+} valence state in the SrVO{sub 2}H film, indicating that the hydrogen existed as hydride. Furthermore, the electronic density of states was highly suppressed at the Fermi energy, consistent with the prediction that tetragonal distortion induces metal to insulation transition.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Environmental Screening Effects in 2D Materials: Renormalization of the Bandgap, Electronic Structure, and Optical Spectra of Few-Layer Black Phosphorus
Few-layer black phosphorus has recently emerged as a potential 2D semiconductor, notable for its widely tunable bandgap, highly anisotropic properties, and theoretically predicted large exciton binding energies. To avoid degradation, it has become common practice to encapsulate black phosphorus devices. It is generally assumed that this encapsulation does not qualitatively affect their optical properties. In this work, we show that the contrary is true. We have performed ab initio GW and GW plus Bethe–Salpeter equation (GW-BSE) calculations to determine the quasiparticle (QP) band structure and optical spectrum of one-layer (1L) through four-layer (4L) black phosphorus, with and without encapsulation between hexagonal boron nitride and sapphire. We show that black phosphorus is exceptionally sensitive to environmental screening. Encapsulation reduces the exciton binding energy in 1L by as much as 70% and completely eliminates the presence of a bound exciton in the 4L structure. The reduction in the exciton binding energies is offset by a similarly large renormalization of the QP bandgap so that the optical gap remains nearly unchanged, yet the nature of the excited states and the qualitative features of the absorption spectrum change dramatically.
2D materials↗
Topochemical Synthesis and Electronic Structure of High-Crystallinity Infinite-Layer Nickelates on an Orthorhombic Substrate
Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward to address these intricate questions is through the growth of high-crystallinity infinite-layer nickelates, including the “parent” phase. Here, we report the synthesis of a high-quality thin-film nickelate, NdNiO 2 . This is achieved through the growth of a perovskite precursor phase (NdNiO 3 ) of superior crystallinity on the NdGaO 3 substrate by off-axis RF magnetron sputtering and a low-temperature topochemical reduction using NaH. We observe a nonlinear Hall effect at low temperatures in this “non-doped” phase. We further study the electronic properties using advanced X-ray scattering and first-principles calculations. We observe spectroscopic indications of the enhanced two-dimensionality and a reduced hybridization of Nd 5d and Ni 3d orbitals. These findings unlock new pathways for preparing high-quality infinite-layer nickelates and provide new insights into the intrinsic features of these compounds.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Observation of Topological Electronic Structure in Quasi-1D Superconductor TaSe3
Not Available
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
The Electron Structure of Metallic Layers in the Quasi-Two-Dimensional Dual-Layered Organic Metal (BETS){sub 4}HgBr{sub 4}(C{sub 6}H{sub 4}Cl{sub 2})
We have studied the behavior of the Shubnikov–de Haas (SdH) oscillations in the quasi-two-dimensional dual-layered organic metal (BETS){sub 4}HgBr{sub 4}(C{sub 6}H{sub 4}Cl{sub 2}). It is established that the spectrum of SdH oscillations in this compound agrees well with theoretical calculations and qualitatively coincides with the analogous spectrum of (ET){sub 4}HgBr{sub 4}(C{sub 6}H{sub 4}Cl{sub 2}) isostructural organic metal. The fractional substitution of sulfur by selenium in the cationic layer strongly decreases the values of cyclotron masses. This decrease is most probably caused by weakening of the electron–phonon interaction.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Benzene derivatives adsorbed to the Ag(111) surface: Binding sites and electronic structure
Dispersion corrected Density Functional Theory calculations were employed to study the adsorption of benzenes derivatized with functional groups encompassing a large region of the activated/deactivated spectrum to the Ag(111) surface. Benzenes substituted with weak activating or deactivating groups, such as methyl and fluoro, do not have a strong preference for adsorbing to a particular site on the substrate, with the corrugations in the potential energy surface being similar to those of benzene. Strong activating (N(CH{sub 3}){sub 2}) and deactivating (NO{sub 2}) groups, on the other hand, possess a distinct site preference. The nitrogen in the former prefers to lie above a silver atom (top site), but in the latter a hollow hexagonal-closed-packed (H{sub hcp}) site of the Ag(111) surface is favored instead. Benzenes derivatized with classic activating groups donate electron density from their highest occupied molecular orbital to the surface, and those functionalized with deactivating groups withdraw electron density from the surface into orbitals that are unoccupied in the gas phase. For benzenes functionalized with two substituents, the groups that are strongly activating or deactivating control the site preference and the other groups assume sites that are, to a large degree, dictated by their positions on the benzene ring. The relative stabilities of the ortho, meta, and para positional isomers of disubstituted benzenes can, in some cases, be modified by adsorption to the surface.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Complex Electronic Structure of Rare Earth Activators in Scintillators
To aid and further the understanding of the microscopic mechanisms behind the scintillator nonproportionality that leads to degradation of the attainable energy resolution, we have developed theoretical and experimental algorithms and procedures to determine the position of the 4f energy levels of rare earth dopants relative to the host band edge states.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Electronic structure of ferromagnetic semiconductor material on the monoclinic and rhombohedral ordered double perovskites La{sub 2}FeCoO{sub 6}
Double perovskite La{sub 2}FeCoO{sub 6} with monoclinic structure and rhombohedra structure show as ferromagnetic semiconductor based on density functional theory calculation. The ferromagnetic semiconductor state can be well explained by the superexchange interaction. Moreover, the ferromagnetic semiconductor state remains under the generalized gradient approximation (GGA) and GGA plus onsite Coulomb interaction calculation.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Ultra-stable trimetallic phosphide heterostructure with regulated electronic structure for overall water splitting at high current densities
Developing ultra-stable electrocatalysts for highly efficient overall water splitting at high current density (HCD) is critical for renewable hydrogen/oxygen production in the industry. However, the most active electrocatalysts for large current-driven water splitting are seriously handicapped by insufficient electrical contact kinetics due to the intensive bubble overflow. Herein, we demonstrate the ultra-stable trimetallic phosphides of NiFeP/NiCoP catalysts on a hydrophilic Ni foam skeleton via a corrosion-hydrothermal-phosphating strategy. The optimized NiFeP/NiCoP catalyst stabilizes for 600 h at -1 A cm -2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution, and it only needs low overpotentials of 237 and 314 mV to drive HER and OER at 1 A cm -2 , respectively. As expected, the optimized NiFeP/NiCoP electrode maintains 1000 h at 0.5 A cm -2 for water splitting, ranking among the top performers among reported catalysts. Such excellent performance could be attributed to the fast electron transfer for electrochemical reactions, the electron-deficient Fe/Ni sites contribute to forming robust metal oxyhydroxide during OER, and electron-rich Co sites facilitate H adsorption during HER. In conclusion, the findings present a highly promising candidate for ultra-stable non-noble metal electrocatalysts, offering a viable option for hydrogen/oxygen supply for fuel cells and metal-air batteries.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Strain effect on electronic structure and thermoelectric properties of orthorhombic SnSe: A first principles study
Strain effect on thermoelectricity of orthorhombic SnSe is studied using density function theory. The Seebeck coefficients are obtained by solving Boltzmann Transport equation (BTE) with interpolated band energies. As expected from the crystal structure, calculated Seebeck coefficients are highly anisotropic, and agree well with experiment. Changes in the Seebeck coefficients are presented, when strain is applied along b and c direction with strength from -3% to +3%, where influence by band gaps and band dispersions are significant. Moreover, for compressive strains, the sign change of Seebeck coefficients at particular direction suggests that the bipolar transport is possible for SnSe.
36 MATERIALS SCIENCE↗
Electronic Structure and Magnetic Properties of Cobalt-Doped Nonstoichiometric Rutile Thin Films
The coherent potential method has been applied for the investigation of Co substitutional doping influence on the spectral and magnetic properties of TiO{sub 2} rutile (100) surface. Both stoichiometric and nonstoichiometric oxygen compositions have been considered. For the stoichiometric case, the energy spectrum corresponds to half-metallic ferromagnet. The Co ions are in 2 + formal oxidation state with a spin magnetic moment of 0.8 μ{sub B}. The presence of oxygen vacancies makes the surface insulating and increases the Co spin magnetic moment value.
36 MATERIALS SCIENCE↗
Regularizing the molecular potential in electronic structure calculations. I. SCF methods
We present a method to remove the singular nuclear potential in a molecule and replace it with a regularized potential that is more amenable to be represented numerically. The singular nuclear potential is canceled by the similarity-transformed kinetic energy operator giving rise to an effective nuclear potential that contains derivative operators acting on the wave function. The method is fully equivalent to the non-similarity-transformed version. We give numerical examples within the framework of multi-resolution analysis for medium-sized molecules.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Electronic structure of CdMoO{sub 4} using Compton scattering technique
The first ever Compton profile of polycrystalline CdMoO{sub 4} has been measured using {sup 137}Cs spectrometer. The results are compared with theoretical Compton profiles deduced from free atom and linear combination of atomic orbitals (LCAO) methods. We have also computed the energy bands using density functional theory (DFT) within LCAO. The computed bands confirm the semiconducting behaviour of this compound. It is seen that the DFT theoretical profile (with local density approximation) gives a better agreement with the experimental Compton data than free atom Compton profile.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Study of Electronic Structure, Magnetism, and Half-Metallicity of New Heusler Compounds CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu)
The density functional calculations were performed using the full-potential linearized augmented plane wave (FPLAPW) method for new Heusler alloys CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu). All compounds were stable in FM AlCu{sub 2}Mn-type structure. Results revealed that these alloys can be experimentally synthesized according to the calculated cohesive and formation energies. CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) alloys in AlCu{sub 2}Mn-type and CuHg{sub 2}Ti-type structures were half-metallic ferromagnets. The origin of half-metallicity in CsNiO{sub 2} alloy was also discussed. The total magnetic moment of CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) alloys in both structures were 3 μ{sub B} per formula unit and obeyed the Slater-Pauling rule (M{sub tot} = 22 − Z{sub tot}). The relationship between the magnetism and half-metallicity of all compounds and the lattice constants was also studied. The half-metallic character in combined alloys CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) improved in comparison with Heusler alloys including transition metals which indicated that they may be good candidates for practical applications in spintronics.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electronic structure and 3d-4f exchange interactions in zircon-type RCrO{sub 4} oxides (R=Dy, Ho and Gd)
Using first principles density functional theory (DFT) calculations within GGA and GGA+U approximations we studied both ferromagnetic (FM) and antiferromagnetic (AFM) phases of zircon type RCrO{sub 4} (R= Dy, Ho, Gd) oxides. We estimated and compared the 3d-4f exchange interaction strengths J between the nearest neighbor R{sup 3+} and Cr{sup 5+} ions for R=Dy, Gd. Our results predict that DyCrO{sub 4}, GdCrO{sub 4} and HoCrO{sub 4} have ferromagnetic ground state which is consistent with experimental observations.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Electronic structure and photovoltaic application of BiI{sub 3}
Rapid recent improvement in photovoltaic efficiency in hybrid lead halide perovskite materials has provided the impetus for understanding other, related main-group halide systems. Here, we show that the closely related but less toxic bismuth iodide BiI{sub 3} can show promising optoelectronic properties. Layered binary BiI{sub 3} is used here as the active layer in planar solar cell architectures (efficiency approximately 0.3%). Experimental and computational studies of absolute band positions of BiI{sub 3} are also presented, to help in the rational design of device architectures that would allow efficient charge transfer at the interfaces.
14 SOLAR ENERGY↗
Tunable electronic structures of p-type Mg doping in AlN nanosheet
The p-type impurity properties are investigated in the Mg-doped AlN nanosheet by means of first-principles calculations. Numerical results show that the transition energy levels reduce monotonously with the increase in Mg doping concentration in the Mg-doped AlN nanosheet systems, and are lower than that of the Mg-doped bulk AlN case for the cases with larger doping concentration. Moreover, Mg substituting Al atom is energy favorably under N-rich growth experimental conditions. These results are new and interesting to further improve p-type doping efficiency in the AlN nanostructures.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗