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Time Projection Chamber (TPC) detectors for nuclear astrophysics studies with gamma beams
摘要： Gamma-Beams at the HI??S facility in the USA and anticipated at the ELI-NP facility, now constructed in Romania, present unique new opportunities to advance research in nuclear astrophysics; not the least of which is resolving open questions in oxygen formation during stellar helium burning via a precise measurement of the12C(??, ??) reaction. Time projection chamber (TPC) detectors operating with low pressure gas (as an active target) are ideally suited for such studies. We review the progress of the current research program and plans for the future at the HI??S facility with the optical readout TPC (O-TPC) and the development of an electronic readout TPC for the ELI-NP facility (ELITPC).
关键词： Gamma-beams,Time Projection Chamber,Optical readout,Stellar helium burning,Nuclear astrophysics,Electronic readout
更新于2025-09-23 15:22:29
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Impact of Defects on Electronic Properties of Heterostructures Constructed From Monolayers of Transition Metal Dichalcogenides
摘要： Electronic properties of heterostructures composed of two single molecular layers (monolayers) of MoS2, WS2, WSe2, and MoSe2 are ab initio simulated with an emphasis to the stacking peculiarities and an influence of point defects in their lattices. MoS2/MoSe2, MoS2/WS2, WS2/WSe2, and MoSe2/WSe2 heterostructures with the monolayers shifted like in the bulk material have been found to behave like semiconductors with the energy gaps of 0.88, 1.25, 1.06, and 1.07 eV, respectively. Such heterostructures possess indirect gaps in contrast to individual monolayers, while direct-gap character is preserved in two layer stacking variants in WS2/WSe2 heterostructures and in MoS2/MoSe2 heterostructure with mirror stacking of the monolayers. Vacancies and Te atoms substituting other chalcogen atoms reduce the band gaps. The calculated orbital compositions of first direct band gap transitions in the defect-free heterostructures and those with the point defects have demonstrated d-electrons of Mo or W atoms to be mainly involved in the transitions.
关键词： defects,two-dimensional crystals,transition metal dichalcogenides,heterostructures,electronic structure
更新于2025-09-23 15:22:29
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Ab-initio study of electronic, optical, thermal, and transport properties of Cr <sub/>4</sub> AlB <sub/>6</sub>
摘要： Theoretical investigation of different physical parameters of Cr4AlB6 have been done within the framework of density functional theory. Cr4AlB6 is a no band gap material. Its Cr-3d states contributes the most at the Fermi level. Thermal properties are investigated using quasi-harmonic Debye model as implemented in Gibbs code for different values of pressure and temperature. Study of transport property suggests that its electrical conductivity increases nonlinearly with increase in temperature but the relative change in its value is very low whereas its thermal conductivity increases linearly with the increase in temperature and relative increase in thermal conductivity is very high. The behavior of Cr4AlB6 is anisotropic and property is ceramic. It has potential applications in making ceramic capacitors. Its reflectivity is high in low energy region. It suggests that material can be used as coating material for far-infrared radiation. Study of the transport property suggests that because of very high value of thermal conductivity, it can be used for heat sink applications.
关键词： optical properties,first principles,electronic properties,thermal properties,thermoelectric transport properties,structural properties
更新于2025-09-23 15:22:29
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Tuning electronic and optical properties of TiO<sub>2</sub> with Pt/Ag doping to a prospective photocatalyst: a first principles DFT study
摘要： Using first-principles density functional theory, the modulated electronic and optical properties of TiO2 with Pt/Ag substitutional dopants with varying concentration are investigated. Our calculations reveal the significant decreasing trend in the band gap of TiO2 while increasing the Pt (direct band gap) and Ag (indirect band gap) impurity concentration from 4.17% to 8.33% to 12.5%. The spin-polarized density of states reveal strong hybridization between the impurity bands with Ti-(3d) and O-(2p) bands near the Fermi level. The charge transfer mechanism depicts the delocalized electron cloud forming a strong bonding between the dopants (Pt/Ag) and oxygen of TiO2. Moreover, the absorption spectra of the Pt doped TiO2 structures have a broad peak at the visible range of energy spectrum with maximum absorption up to 0.7×10?5cm?1. The calculated reflectivity, energy loss function and extinction coefficient shows the enhanced optical properties of doped TiO2 compared to its pristine form. The obtained results predict the way to tailor the optical properties of Pt/Ag-doped TiO2 as an efficient photocatalyst in the visible region.
关键词： Pt,Optical properties,Electronic structure,Photocatalyst,Ag doped TiO2
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 6th Workshop on Advances in Information, Electronic and Electrical Engineering (AIEEE) - Vilnius, Lithuania (2018.11.8-2018.11.10)] 2018 IEEE 6th Workshop on Advances in Information, Electronic and Electrical Engineering (AIEEE) - 18-pulse Rectifier with Electronic Phase Shifting with Autotransformer in Inverter and Rectifier Mode
摘要： To reduce harmonic distortion of the input current, multipulse rectifiers are used. They require the presence of phase-shifting transformers or autotransformers. Elimination of electromagnetic phase-shifting devices while maintaining small harmonic distortion of the input current and obtaining a power factor close to unity is possible with the use of electronic phase shift. The electronic phase shift is realized by means of the rectifier itself: the introduction of positive and negative control angles in the pairs of rectifiers’ modules. At present, 12-pulse rectifiers with electronic phase shift are known. Unlike classic rectifiers, they do not use phase-shifting transformers and have a unit power factor. Increasing of the rectifier’s pulse makes it possible to improve the harmonic composition of the input current. The use of the principle of electronic phase shift in 18-pulse rectifier leads to different levels of constant voltage at the output of the rectifiers. In this case, to equalize the currents of rectifiers’ modules, one can use both an increase the voltage at the input of rectifiers operating with large control angles and a decrease the input voltage of the rectifiers operating with smaller control angles. The principles of constructing of matching autotransformers for the 18-pulse rectifier with an electronic phase shift are considered in the article. Comparison of 18-pulse rectifiers with use of step-up and step-down autotransformers is made. Data on the installed capacity of autotransformers, power losses are obtained. The results of thermophysical modeling are presented. When comparing the parameters of the matching magnetic elements, it can be concluded that it is more appropriate to use a step-down autotransformer.
关键词： pulse-width modulation,magnetic elements,electronic phase shifting,rectifiers,power factor
更新于2025-09-23 15:22:29
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Resonant inelastic x-ray incarnation of Young’s double-slit experiment
摘要： Young’s archetypal double-slit experiment forms the basis for modern diffraction techniques: The elastic scattering of waves yields an interference pattern that captures the real-space structure. Here, we report on an inelastic incarnation of Young’s experiment and demonstrate that resonant inelastic x-ray scattering (RIXS) measures interference patterns, which reveal the symmetry and character of electronic excited states in the same way as elastic scattering does for the ground state. A prototypical example is provided by the quasi-molecular electronic structure of insulating Ba3CeIr2O9 with structural Ir dimers and strong spin-orbit coupling. The double “slits” in this resonant experiment are the highly localized core levels of the two Ir atoms within a dimer. The clear double-slit-type sinusoidal interference patterns that we observe allow us to characterize the electronic excitations, demonstrating the power of RIXS interferometry to unravel the electronic structure of solids containing, e.g., dimers, trimers, ladders, or other superstructures.
关键词： Resonant inelastic x-ray scattering,quasi-molecular orbitals,electronic excitations,Young's double-slit experiment,spin-orbit coupling,interference patterns
更新于2025-09-23 15:22:29
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Stacking effect on electronic, photocatalytic and optical properties: A comparison between bilayer and monolayer SnS
摘要： In this work, the stacking-dependent optoelectronic performances of a bilayer SnS were explored based on density functional theory (DFT). The results demonstrated that an AB-stacking induces an indirect-to-direct transition, a feature that is capable of vanquishing electron transition impediment from an intrinsic indirect monolayer SnS. An anisotropic and small carrier effective mass exists in all the stacking models, among which the AB-stacking with the lowest value favors high carrier mobility. Calculated band alignments are indicative of acceptable and adjustable photocatalytic activity for all the stacking models, unlike the monolayer SnS. The AB-stacking configuration possesses the strongest redox power, which facilitates it to be a potential candidate for photocatalytic water splitting. Additionally, the AB-stacking does effectively improve optoelectronic properties. The study demonstrated that layer-stacking is an availably adjustable method in the fields of sunlight-driven photocatalysis for nano-optoelectronic devices.
关键词： Electronic properties,Density functional theory,Stacking models,Optical properties,Photocatalytic properties
更新于2025-09-23 15:21:21
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: A first-principles study
摘要： For environmental reasons there is a need for alternative Cd-free buffer materials in Cu(In,Ga)(S,Se)2 (CIGSSe) based thin film solar cells. In this context, β-In2S3 is one candidate material, whose optoelectronic properties can be affected by the presence of impurities. In this study, we investigate the impact of O and Cl impurities on the electronic and optical behavior of β-In2S3 by means of electronic structure calculations within density functional theory using hybrid functionals. We find that β-In2S3 is thermodynamically stable being in contact with both O and Cl reservoirs. Furthermore, we present evidence that O on interstitial sites (Oi) and Cl on 8c In sites (ClIn) cause low-temperature persistent electron photoconductivity. At room temperature, defect levels associated with Cl on S sites (ClS, ClS(cid:2) , and ClS(cid:2)(cid:2) ) get thermally ionized and release free electrons into the system. Thus, the n-type conductivity of the In2S3 buffer layer increases. O impurities on S sites, in contrast, are electrically inert. Hence, we conclude that intentional doping by Cl is a means to improve the properties of β-In2S3 serving as buffer material.
关键词： β-In2S3,hybrid functionals,O and Cl impurities,n-type conductivity,density functional theory,persistent electron photoconductivity,electronic structure calculations
更新于2025-09-23 15:21:21
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<i>l</i> -Stercobilin-HCl and <i>d</i> -Urobilin-HCl. Analysis of Their Chiroptical and Conformational Properties by VCD, ECD, CPL Experiments and MD, DFT Calculations
摘要： Vibrational circular dichroism (VCD) and IR spectra of dichloromethane solutions of l-stercobilin and d-urobilin hydrochlorides have been recorded in the mid-IR region. The spectra are best interpreted by combining molecular dynamics (MD) calculations and DFT calculations within the QM/MM ONIOM-type framework, and the combined predicted results are better and more informative than the more standard analysis provided by DFT calculations. The same approach also sheds light on the Cotton effect sign inversion of room temperature versus low temperature electronic CD (ECD) spectra of the same compounds in methanol-glycerol solution. Finally, circularly polarized luminescence (CPL) spectra for l-stercobilin in chloroform solution provide information on the excited state geometry of this molecule.
关键词： Vibrational circular dichroism,electronic CD,molecular dynamics,IR spectra,QM/MM ONIOM-type framework,Cotton effect,circularly polarized luminescence,DFT calculations
更新于2025-09-23 15:21:21
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The electronic and elasticity properties of new half-metallic chalcogenides Cu <sub/>3</sub> TMCh <sub/>4</sub> (TM?=?Cr, Fe and Ch?=?S, Se, Te): an <i>ab initio</i> study
摘要： The ternary copper-based chalcogenides Cu3TMCh4 (TM = Cr, Fe and Ch = S, Se, Te), which have simple cubic (SC) crystal structure and conform to P(cid:1)43m space group with 215 space number, have been investigated by spin-polarised generalised gradient approximation (GGA) in the framework of density functional theory (DFT). All systems have been considered in ferromagnetic (FM) order. The mechanical and thermal properties and the electronic band structures of these systems have been investigated after the well-optimised structural parameters have been obtained. The spin-polarised electronic band structures of all the systems exhibit half-metallic behaviour with band gaps in minority spin channel from 0.29 eV for Cu3FeTe4 to 1.08 eV for Cu3CrS4, while metallic band structures are observed for majority spins. This agrees with the calculated total magnetic moments which are close to integer values. The calculated negative formation enthalpies indicate the energetic and thermodynamic stability of these compounds. Moreover, the calculated elastic constants verify that these materials are stable mechanically due to satisfying Born stability criteria. The estimated anisotropy shear factors show that Cu3FeS4, Cu3FeSe4 and Cu3CrSe4 systems have nearly isotropic character with 1.004, 0.910, and 0.958 values, respectively, whereas other compounds have relatively low anisotropic behaviour.
关键词： electronic structure of bulk materials,density functional theory,chalcogenides,Half-metallic,mechanical properties of solids
更新于2025-09-23 15:21:21