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Holographic fabrication of octagon graded photonic supercrystal and potential applications in topological photonics
摘要： Novel optical properties in graded photonic super-crystals can be further explored if new types of graded photonic super-crystals are fabricated. In this paper, we report holographic fabrication of graded photonic super-crystal with eight graded lattice clusters surrounding the central non-gradient lattices through pixel-by-pixel light modulator. The phase engineering in a spatial prospect of applications of octagon graded photonic super-crystal in topological photonics is discussed through photonic band gap engineering and coupled ring resonators.
关键词： 2D photonic crystal,photonic band structure,holographic fabrication,graded photonic super-crystal
更新于2025-09-11 14:15:04
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Highly efficient perovskite solar cells based on a Zn2SnO4 compact layer
摘要： In the present work, a new reflux condensation route has been developed for synthesizing Zn2SnO4 film, which was first used as a compact layer in a perovskite solar cell (PSC), and achieved an efficiency of 20.1%. The high efficiency of PSC could be contributed to the following: i) As a compact layer in a PSC, Zn2SnO4 exhibits high electron mobility and has an appropriate energy band structure, resulting in the efficient extraction of carriers and transport of electrons; ii) the surface of the FTO substrate is completely covered by a Zn2SnO4 compact layer, and the direct contact between a perovskite layer and FTO is prevented, leading to significantly efficiently suppression of charge recombination. Consequently, the cell consisting of a Zn2SnO4 compact layer exhibits excellent photovoltaic performance.
关键词： Zn2SnO4,photovoltaic property,compact layer,perovskite solar cells,charge recombination,energy band structure
更新于2025-09-11 14:15:04
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Influence of the Cation on the Surface Electronic Band Structure and Magnetic Properties of Mn:ZnS and Mn:CdS Quantum Dot Thin Films
摘要： The effects of doping Mn into ZnS and CdS quantum dots are reported. Scanning tunneling spectroscopy spectra show a reduction in the electronic band gap in both CdS and ZnS upon incorporation of the Mn dopant. Mn:ZnS exhibits a rigid band shift toward higher bias which is reminiscent of a hole doping effect. This rigid band shift in Mn:ZnS is argued, with the help of X-ray photoelectron spectroscopy, to be due to a hole-doping mechanism caused by the favorable formation of Zn vacancies and a reduction in S vacancies compared to undoped ZnS films. In CdS no rigid band shift is observed even though the presence of Cd vacancies can be confirmed by photoemission and magnetic measurements. A strong sp-d hybridization is observed in the Mn:CdS film upon introducing the Mn dopant. d0 ferromagnetism is observed in both undoped ZnS and CdS quantum dot thin films at room temperature. Upon doping of Mn into ZnS the magnetization is reduced suggesting an antiparallel alignment of Mn-Mn or Mn-Zn vacancies nearest neighbors. Density Functional Theory supports the experimental results indicating the nearest neighbor Mn atoms prefer antiparallel alignment of their magnetic moments with preferred ground state of Mn in 3+ oxidation state.
关键词： CdS,Mn doping,quantum dots,magnetic properties,scanning tunneling spectroscopy,electronic band structure,X-ray photoelectron spectroscopy,density functional theory,ZnS
更新于2025-09-11 14:15:04
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Exploring materials band structure space with unsupervised machine learning
摘要： An unsupervised machine learning algorithm is applied for the first time to explore the space of materials electronic band structures. T-student stochastic neighbor embedding (t-SNE), a state of the art algorithm for visualization of high dimensional data, is applied on feature spaces constructed by extracting electronic fingerprints straight from Brillouin zone of the materials. Different spaces are designed and mapped to lower dimensions allowing to analyze and explore this previously uncharted band structure space for thousands of materials at once. In all cases analyzed machine learning was able to learn and cluster the materials depending on the features involved. t-SNE promises to be a extremely useful tool for exploring the materials space.
关键词： Fermiology,Data visualization,Band structure,Unsupervised machine learning,Data mining,Materials informatics,High throughput materials calculations
更新于2025-09-11 14:15:04
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Light-Induced Current Oscillations in the Charge-Ordered State of (TMTTF)2SbF6
摘要： Below TCO = 157 K the quasi-one-dimensional charge-transfer salt (TMTTF)2SbF6 undergoes a pronounced phase transition to a charge-ordered ground state. We have explored the non-linear and photoconductive behavior as a function of applied voltage, laser pulse energy and temperature. Besides a decay of the photoconductive signal in a double exponential fashion in the millisecond range, we discover current oscillations in the kHz range induced by the application of short laser pulses. While the resonance frequencies do not depend on voltage or laser intensity and vary only slightly with temperature, the amplitude changes linearly with the laser intensity and voltage. We suggest that photo-induced fluctuations of the charge-ordered state alter the current flow of the single particles and hence, the photocurrent. The findings are discussed and compared to comparable phenomena in other low-dimensional electron systems.
关键词： TMTTF,non-linear transport,calculations of band structure and optical conductivity,charge-transfer salts,photoconductivity,current oscillations,charge-order phase transition
更新于2025-09-11 14:12:44
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Complex band structure calculations based on the overbridging boundary matching method without using Green's functions
摘要： A complex band structure describes the dispersion relation not only of propagating bulk states but also of evanescent ones, both of which are together referred to as generalized Bloch states and are important for understanding the electronic nature of solid surfaces and interfaces. On the basis of the real-space finite-difference formalism within the framework of the density functional theory, we formulate the Kohn-Sham equation for generalized Bloch wave functions as a generalized eigenvalue problem without using any Green’s function matrix. By exploiting the sparseness of the coefficient matrices and using the Sakurai-Sugiura projection method, we efficiently solve the derived eigenvalue problem for the propagating and slowly decaying/growing evanescent waves, which are essential for describing the physics of surface/interface states. The accuracy of the generalized Bloch states and the computational efficiency of the present method in solving the eigenvalue problem obtained are compared with those by other methods using the Green’s function matrix. In addition, we propose two computational techniques to be combined with the Sakurai-Sugiura projection method and achieve further improvement in the accuracy and efficiency. Complex band structures are calculated with the present method for single- and multiwall carbon nanotubes, and the interwall hybridization and branch points of evanescent electronic states observed in the imaginary parts of the band structures are also discussed.
关键词： Sakurai-Sugiura projection method,density functional theory,generalized Bloch states,carbon nanotubes,complex band structure
更新于2025-09-10 09:29:36
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Light-emitting 9R-Si phase formed by Kr <sup>+</sup> ion implantation into SiO <sub/>2</sub> /Si substrate
摘要： Light-emitting layers of hexagonal 9R silicon were synthesized by ion implantation into SiO2/Si substrates. Using cross-sectional transmission electron microscopy, the formation of a 9R phase in a cubic silicon substrate near the interface with silicon dioxide under irradiation with Krt ions (80 keV) and subsequent annealing at 800 (cid:2)C is demonstrated. Arguments explaining how the new phase is formed through hexagonalization of the initial cubic silicon are presented. The synthesized 9R-Si layers are characterized by a low-temperature photoluminescence line with the maximum at a wavelength around 1240 nm. First-principles calculations of the 9R-Si electronic band structure showed that this material is an indirect-gap semiconductor with the bandgap value of 1.06 eV, which is in good agreement with the spectral position of the experimentally observed photoluminescence line. Believing that the proposed approach can be extended to other semiconductors, we calculated the electronic band structure of 9R germanium and predicted that the hexagonalization converts cubic Ge into a direct-gap semiconductor with the bandgap of 0.48 eV.
关键词： hexagonal silicon,photoluminescence,electronic band structure,9R-Si,ion implantation
更新于2025-09-10 09:29:36
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Synthesis, Optical and Magnetic Properties of Six-Layered Aurivillius Bismuth Ferrititanate
摘要： This work reports the preparation, structure, photochemical and magnetic properties of six-layered Aurivillius bismuth ferrititanates, i.e., Bi7Ti3Fe3O21, Bi7(Ti2Nb)Fe3O21+δ and Bi7(Ti2Mg)Fe3O21-δ nanoparticles. The samples were prepared through the modified citrate-complexation and precursor film process. XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated via some measurements such as SEM, TEM, and EDX analyses. Bi7Ti3Fe3O21, Bi7(Ti2Nb)Fe3O21+δ and Bi7(Ti2Mg)Fe3O21-δ nanoparticles present an indirect allowed transitions with band energy of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet2g+Bi6s) build up the valence band (VB), and electronic components of (Ti-3d+Fe-eg) form the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. Three samples have obvious abilities on the photocatalytic degradation on Rhodamine B (RhB) dyes via the excitation wavelength λ> 420 nm. The optical absorption, photodegradation and magnetic abilities were improved through micro-structural modification on “B” site via partial substitution of Mg2+- and Nb5+- for Ti4+. The photocatalytic results were discussed on the layer structure and multivalent Fe ions. Fe3+/2+ in the perovskite slabs (Bi5Fe3Ti3O19)2? could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi7(Ti2Mg)Fe3O21-δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.
关键词： Nanoparticles,Layered perovskites,Band structure,Semiconductors,Photocatalysis,Aurivillius phases
更新于2025-09-10 09:29:36
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Influence of Crystal Structure and 3d Impurities on the Electronic Structure of the Topological Material Cd3As2
摘要： This paper presents a theoretical study of the effects of crystal structure and Mn and Co substitutions for Cd on the electronic structure of the topological material Cd3As2. We have carried out density functional theory calculations of the band structure and density of states in tetragonal and cubic Cd3As2, as well as in Cd3 – xMnxAs2 and Cd3 – xCoxAs2 crystals. The results indicate that the band structure of the cubic Cd3As2 phase differs significantly from that of a Dirac semimetal, characteristic of the tetragonal phase. It has also been shown that, after Co substitution for 1/24 of the Cd atoms, the structure of the density of 3d electron states is similar to that of the density of states in the magnetic semiconductor Cd3 – xMnxAs2, with a characteristic minimum at the Fermi energy. At the same time, in the case of analogous Mn substitution for Cd, the density of d-electron states has no such minimum.
关键词： Mn,density functional theory (DFT) calculations,magnetic semiconductors,topological materials,Co,Cd3As2,Dirac semimetal,band structure,density of states (DOS)
更新于2025-09-10 09:29:36
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Structural, elastic, electronic, thermodynamic, and optical properties of layered BaPd2As2 pnictide superconductor: A first principles investigation
摘要： BaPd2As2, belonging to the 122 pnictide group, is an iron-free layered transition metal arsenide which exhibits superconductivity at low temperature when realized in the ThCr2Si2 type structure (I4/mmm). We have performed density functional theory (DFT) based calculations to investigate the structural, elastic, electronic, thermodynamic, and optical properties of BaPd2As2 in this study. The structural, elastic, and the band structure features are compared with the available experimental and theoretical results. Pressure and temperature dependences of various important thermodynamic functions, e.g., bulk modulus, specific heats at constant pressure and volume, coefficient of volume thermal expansion, and Debye temperature are studied in details for the first time. The optical parameters of BaPd2As2 are also studied in details for the first time. The optical properties compliment the electronic band structure characteristics. Optical constants show significant dependence of the state of polarization of the incident electric field. BaPd2As2 exhibits high reflectance in the infrared and near-visible region and strongly absorbs the ultraviolet radiation. The relevance of the electronic energy density of states and the characteristic phonon frequency to superconductivity in BaPd2As2 is also discussed.
关键词： BaPd2As2 superconductor,Density functional theory,Electronic band structure,Optical properties,Elastic constants,Thermodynamic properties
更新于2025-09-10 09:29:36