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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Atomic and Electronic Structure of Silicene on Ag: A Theoretical Perspective
摘要： The isolation of graphene sheets from its parent crystal graphites has given the kick to experimental research on its prototypical 2D elemental cousin, silicene [1]. Unlike graphene, silicene lacks a layered parent material from which it could be derived by exfoliation. Hence, the efforts of making the silicene dream a reality were focused on epitaxial growth of silicene on substrates. The first synthesis of epitaxial silicene on silver (111) [27, 46] and zirconium diboride templates [16] and next on an iridium (111) surface [31], has boosted research on other elemental group IV graphene-like materials, namely, germanene and stanene [30, 48]. The boom is motivated by several new possibilities envisaged for future electronics, typically because of the anticipated very high mobilities for silicene and germanene [49], as well as potential optical applications [30]. It is also fuelled by their predicted robust 2D topological insulator characters [14, 28] and potential high temperature superconductor character [5, 50]. One of the most promising candidates as a substrate is Ag because from the studies of the reverse system, where Ag atoms were deposited on silicon substrate, it was known that Ag and silicon make sharp interfaces without making silicide compounds.
关键词： theoretical perspective,electronic structure,silicene,Ag(111),epitaxial growth
更新于2025-09-23 15:21:21
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Electronic, Optical and Elastic Properties of Cu2CdGeSe4: A First-Principles Study
摘要： Using the augmented plane wave + local orbitals method with different approximation functionals, we investigate systematically the electronic, optical and elastic properties of stannite-type Cu2CdGeSe4. Among different approximation functionals, the modi?ed Becke–Johnson (mBJ) potential with Hubbard-corrected parameter U (mBJ + U) gives the most reliable results on the electronic properties of Cu2CdGeSe4 in comparison with the experimental data. Elastic modulus, elastic constants and the Poisson’s ratio of Cu2CdGeSe4 were calculated using the Elastic software package. Optical properties such as wide spectrum of absorbed photon energy, namely 1.3–27.2 eV, high absorption coef?cient (above 104 cm?1) and optical anisotropy suggest the application of Cu2CdGeSe4 in solar cells.
关键词： electronic structure,optical properties,Optical materials,elastic properties,ab initio calculations
更新于2025-09-23 15:21:21
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Improved Electronic Structure and Optical Performance of Bi2Te3-xSex From First-principle Calculations Within TB-mBJ Exchange Potential
摘要： Using the first-principle calculations of density functional theory within the (FP-LAPW) method, we have investigated the structural, electronic and optical properties of Bi2Te3-xSex alloys with compositions x = 0, 1, 2 and 3 of Se. The generalized gradient approximation functional of Wu and Cohen (GGA-PBE) is used to calculate ground state structural parameters of Bi2Te3-xSex , which are in good agreement with theoretical and experimental data. The electronic band structures and optical constants have been improved with Tran-Blaha modified Becker-Johnson (TB-mBJ) parameterization scheme. Also, we have analyzed in detail the performance of dielectric function, refractive index, reflectivity and optical conductivity of these alloys. Our results show that Bi2Te3-xSex alloys are promising candidates for optoelectronic applications especially in the Infrared and visible fields. Bi2Te3-xSex materials have a direct band gap and can be tuned from 0.1706 eV to 0.7819 eV by varying In composition so emission was tunable from 1.58 to 7.26 micrometers (infrared field), in addition for their direct band gap and in view of their attractive optical properties such conductivity, absorption and reflectivity these materials is considered as promising materials for optoelectronic applications.
关键词： Electronic structure,TB-mBJ,Optical properties,First-principle calculations
更新于2025-09-23 15:21:21
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Extrinsic Defects in Crystalline MoO <sub/>3</sub> : Solubility and Effect on the Electronic Structure
摘要： The effect of six potential contaminants (Cu, In, Ga, Se, Sn and Zn) and five potential dopants (Ti, Mn, Sc, V and Y) on the electronic and optical properties of molybdenum oxide (MoO3) contact layers for solar cells was investigated using point defect analysis informed by density functional theory simulations. Of the contaminants investigated, Sn, In and Ga were found to be highly insoluble at all relevant temperatures and pressures, and therefore not a concern for solar cell manufacturing. Zn, Cu and Se exhibit some solubility, with the latter two appearing to introduce detrimental defect states near the valence band. This contamination can be avoided by increasing the O2 partial pressure during MoO3 deposition. Out of five potential aliovalent dopants, Sc, Ti and Y were disregarded due to their limited solubility in MoO3, while V was found to be highly soluble and Mn somewhat soluble. The effect of Mn and V doping was shown to be strongly dependent on the O2 partial pressure during deposition with a high pO2 favoring the formation of substitutional defects (potentially beneficial in the case of Mn doping due to the addition of defects states near the conduction band) while low pO2 favors interstitial defects.
关键词： electronic structure,solubility,solar cells,molybdenum oxide,extrinsic defects,point defect analysis,density functional theory,MoO3
更新于2025-09-23 15:21:21
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Photofragment Translational Spectroscopy Studies of H Atom Loss Following Ultraviolet Photoexcitation of Methimazole in the Gas Phase
摘要： The ultraviolet (UV) photodissociation of gas phase methimazole has been investigated by H Rydberg atom photofragment translational spectroscopy methods at many wavelengths in the range 222.5 – 275 nm and by complementary electronic structure calculations. Methimazole is shown to exist predominantly as the thione tautomer, 1-methyl-2(3H)-imidazolinethione, rather than the commonly given thiol form, 2-mercapto-1-methylimidazole. The UV absorption spectrum of methimazole is dominated by the S4←S0 transition of the thione tautomer, which involves electron promotion from an a′ (py) orbital localized on the sulfur atom to a σ* orbital localized around the N–H bond. Two H atom formation pathways are identified following UV photoexcitation. One, involving prompt, excited state N–H bond fission, yields vibrationally cold but rotationally excited methimazolyl (Myl) radicals in their first excited (??) electronic state. The second yields H atoms with an isotropic recoil velocity distribution peaking at low kinetic energies but extending to the energetic limit allowed by energy conservation given a ground state dissociation energy D0(Myl–H) ~24 000 cm-1. These latter H atoms are attributed to the unimolecular decay of highly vibrationally excited S0 parent molecules. The companion electronic structure calculations provide rationales for both fragmentation pathways and the accompanying product energy disposals, and highlight similarities and differences between the UV photochemistry of methimazole and that of other azoles (e.g. imidazole) and with molecules like thiourea and thiouracil that contain similar N–C=S motifs.
关键词： methimazolyl radicals,unimolecular decay,H Rydberg atom photofragment translational spectroscopy,ultraviolet photodissociation,N–H bond fission,methimazole,electronic structure calculations,thione tautomer
更新于2025-09-23 15:21:21
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A general approach for the calculation and characterization of x-ray absorption spectra
摘要： We present a general approach for the calculation and assignment of X-ray absorption spectra based on electronic wavepacket propagations performed using explicitly time-dependent electronic structure calculations. Such calculations have the appeal of yielding the entire absorption spectrum for the cost of a single set of electronic wavepacket propagations, obviating the need to explicitly calculate large numbers of core-excited states. The spectrum can either be calculated from the Fourier transform of the time-dependent dipole moment or from the Fourier transform of the wavepacket autocorrelation function. We propose that calculating the absorption spectrum using the latter approach will generally be the preferred option. This method has two important advantages. First, the autocorrelation functions can be obtained for twice the propagation time, resulting in a halving of the computational effort required to calculate the spectrum relative to the time-dependent dipole moment approach. Second, using the tools of filter diagonalisation, the autocorrelation functions may be used to determine the time-independent final core-excited states underlying the peaks of interest in the spectrum. The proposed scheme is validated by calculating and characterizing the X-ray absorption spectra of benzene and trifluoroacetonitrile at the time-dependent second-order algebraic diagrammatic construction level of theory.
关键词： time-dependent electronic structure calculations,X-ray absorption spectra,core-excited states,electronic wavepacket propagations,filter diagonalisation
更新于2025-09-23 15:21:01
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Atomic and electronic structure of ferroelectric La-doped HfO<sub>2</sub> films
摘要： The atomic structure and optical properties of ferroelectric La-doped hafnium oxide (La:HfO2) thin films grown by the plasma-assisted atomic layer deposition were investigated. Using high resolution transmission electron microscopy, it was shown that the studied La:HfO2 film has a orthorhombic polar structure with the P mn21 space group. It was found that the film exhibits ferroelectric properties. By means of X-ray photoelectron spectroscopy and specroellipsometry it was established that La:HfO2 consists of the HfO2 and La2O3 phases mixture. The specroellipsometry analysis with the Bruggeman effective medium approximation showed that the investigated La:HfO2 consists of 88% HfO2 and 12% La2O3. It is shown that etching La:HfO2 with argon ions leads to the oxygen vacancies generation in the near-surface region. These vacancies are generated mainly due to the knocking out of oxygen atoms to the interstitial positions, and the following annealing at 700 ℃ in vacuum for 1 hour leads to the annihilation of that Frenkel defects.
关键词： ferroelectric,XPS,electronic structure,plasma-assisted atomic layer deposition,atomic structure,La-doped HfO2,specroellipsometry,HRTEM
更新于2025-09-23 15:21:01
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Modifying the geometric and electronic structure of hexagonal boron nitride on Ir(111) by Cs adsorption and intercalation
摘要： Epitaxial hexagonal boron nitride on Ir(111) is significantly modified by adsorption and intercalation of alkali-metal atoms. Regarding geometry, intercalation lifts the two-dimensional layer from its substrate and reduces the characteristic corrugation imprinted by direct contact with the metal substrate. Moreover, the presence of charged species in close proximity to the hexagonal boron nitride (hBN) layer strongly shifts the electronic structure (valence bands and core levels). We used scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and the x-ray standing wave technique to study changes in the atomic structure induced by Cs adsorption and intercalation. Depending on the preparation, the alkali-metal atoms can be found on top and underneath the hexagonal boron nitride in ordered and disordered arrangements. Adsorbed Cs does not change the morphology of hBN/Ir(111) significantly, whereas an intercalated layer of Cs decouples the two-dimensional sheet and irons out its corrugation. XPS and angle-resolved photoelectron spectroscopy reveal a shift of the electronic states to higher binding energies, which increases with increasing density of the adsorbed and intercalated Cs. In the densest phase, Cs both intercalates and adsorbs on hBN and shifts the electronic states of hexagonal boron nitride by 3.56 eV. As this shift is not sufficient to move the conduction band below the Fermi energy, the electronic band gap must be larger than 5.85 eV.
关键词： hexagonal boron nitride,Cs adsorption,electronic structure,geometric structure,intercalation
更新于2025-09-23 15:21:01
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On the Construction of Quasi-Diabatic Hamiltonians That Accurately Represent Ab Initio Determined Adiabatic Electronic States Coupled by Conical Intersections for Systems With on the Order of 15 Atoms. Application to Cyclopentoxide Photoelectron Detachment in the Full 39 Degrees of Freedom
摘要： We present, for systems of moderate dimension, a fitting framework to construct quasi-diabatic Hamiltonians that accurately represent ab initio adiabatic electronic structure data including the effects of conical intersections. The framework introduced here minimizes the difference between the fit prediction and the ab initio data obtained in the adiabatic representation, which is singular at a conical intersection seam. We define a general and flexible merit function to allow arbitrary representations and propose a representation to measure the fit-ab initio difference at geometries near electronic degeneracies. A fit Hamiltonian may behave poorly in insufficiently sampled regions, in which case a machine learning theory analysis of the fit representation suggests a regularization to address the deficiency. Our fitting framework including the regularization is used to construct the full 39-dimensional coupled diabatic potential energy surfaces for cyclopentoxy relevant to cyclopentoxide photoelectron detachment.
关键词： cyclopentoxide photoelectron detachment,quasi-diabatic Hamiltonians,ab initio electronic structure,potential energy surfaces,conical intersections
更新于2025-09-23 15:21:01
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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Electronic Structure of Oxide Ultrathin Layers on Metal Surfaces
摘要： Since about 35 years ago, the development of the electron microscopy and spectroscopy techniques has pushed the scienti?c community toward the fabrication of physical systems with a reduced “vertical” dimension, down to nanometer size and ultimately to the monolayer (ML) or single-atom thickness. Especially at the beginning, a requirement for these ultra-thin systems was that these should be grown on metallic or at least semiconducting substrates in order to exploit the enhanced resolution of surface science techniques available when working with conductive systems. Oxide systems were no exception to this trend, and systems made by one or very few oxide layers grown onto metallic substrates were indeed achieved and started to be thoroughly characterized.1,2 Another push to research on oxide ultra-thin ?lms was provided by semiconductor device technology, in which silicon chips are covered by a nanometer-size ?lm of amorphous silica, by the efforts in understanding metal corrosion, by the study of thin insulating oxide ?lms in storage devices, and by the study of oxide supports in heterogeneous catalysis. The ?eld however evolved independently of these initial drives especially as it became clear that the properties of these materials, such as transport and electronic structure, were strongly in?uenced by their detailed and unusual structure. Quite soon, in fact, it was realized that these systems in most cases were not a mere reproduction of the bulk oxides on a reduced scale, but represented completely new hybrid metal/oxide systems with novel structural and electronic properties, often with no counterpart in the bulk. This was unequivocally demonstrated when the atomistic structure of some of these phases was unveiled via the combined use of microscopy and computational characterization,3–5 which allowed researchers to investigate not only the novel structures thus produced, but also the corresponding electronic and spectroscopic properties in great detail. It was the birth of the ?eld of UltraThin Oxides (UTOx) on metal surfaces, whose theoretical or electronic structure description is the topic of this essay.
关键词： Oxide Ultrathin Layers,Electronic Structure,UltraThin Oxides,Metal Surfaces,UTOx
更新于2025-09-23 15:21:01