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Surface Nonlinear Optics on Centrosymmetric Dirac Nodal‐Line Semimetal ZrSiS
摘要： Gapless surface states (SSs) are features of topological semimetals and are extensively observed. Nowadays, the emerging question is whether the SSs possess exotic and applicable properties. Here, associated with the symmetrical selection rule for nonlinear optical materials, the surface nonlinear optics on a centrosymmetric Dirac nodal-line semimetal ZrSiS crystal is studied and it is found that the SSs bring record nonlinear susceptibilities. The unprecedented conversion efficiencies for second and third harmonic generations are 0.11‰ and 0.43‰, respectively, more than ten orders of magnitude larger than the typical surface second harmonic generation. This work discovers a new route toward studying the SSs for applications in nonlinear photonics.
关键词： density functional theory calculations,ZrSiS,surface states,nonlinear optics,symmetry breaking
更新于2025-09-11 14:15:04
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Effects of Gas-Phase Conditions and Particle Size on the Properties of Cu(111)-Supported Zn <sub/>y</sub> O <sub/>x</sub> Particles Revealed by Global Optimisation and Ab Initio Thermodynamics
摘要： The characterisation of the interaction between nano- or sub-nano- particles with a support nowadays increasingly relies on computational modelling by means of the density functional theory calculations. These provide valuable atomic-detail understanding of the structure and energetics of supported clusters, but it is still challenging to find (or design) structural models that are representative of real systems in terms of size, structure, and composition. In this study, we have applied an extensive and systematic approach combining global optimisation based on an evolutionary algorithm with atomistic ab initio thermodynamics for finding stable structures of a relevant material for catalytic methanol synthesis: Cu(111)-supported ZnyOx clusters. We identify the ZnO3 motif as the elementary building block of such clusters, on which we recently have investigated the full catalytic process for methanol synthesis. With the collection of global minima of Cu(111)-supported ZnyOx clusters resulting from this large-scale global optimisation effort, we assess the effect of size, gas-phase conditions, and support interactions on the phase diagrams, reactivity, and structural properties of the ZnyOx particles. We find moderate size-effects that are mostly related to the differences in stable Zn:O ratios of the identified global minima and to the formation of different sites in larger clusters. In contrast, large differences in the oxidation state of the clusters as defined by the gas-phase conditions significantly affect the geometry, electronic structure, and reactivity of the ZnyOx particles. This highlights the importance of thoroughly sampling structures with different stoichiometry and appropriately assessing their stability using a detailed thermodynamics analysis.
关键词： global optimisation,Cu(111)-supported ZnyOx clusters,ab initio thermodynamics,density functional theory,methanol synthesis
更新于2025-09-11 14:15:04
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Single-step formation of Cr 2 N nanoparticles by pulsed laser irradiation
摘要： Chromium nitride nanoparticles with mean diameter distribution between 0.8 nm and 30 nm were produced by laser irradiation of a chromium target immersed in liquid nitrogen. Cr was directly converted to chromium nitride nanoparticles according to selected-area electron diffraction analyses using the transmission electron microscopy technique. Crystalline nanoparticles mostly consist of Cr2N, which is commonly reported together with the conversion of Cr2N to CrN and the mixture of chromium oxides. In addition, there is no evidence of oxidation by storage or photodegradation of the nanoparticles in isopropyl alcohol suspensions. The intensity profile of small-angle X-ray scattering indicates that the geometrical shape of the nanoparticles is not spherical but cylindrical with aspect ratio (height-to-radius) of 0:35–0:05. UV-Vis absorption spectroscopy reveals the presence of surface plasmon absorption at the ultraviolet region at wavelengths of 350, 372, and 397 nm. First-principles calculations of density of states, dielectric function, and optical conductivity performed within the theoretical framework of density functional theory for Cr2N with a hexagonal structure corroborate the formation of surface plasmons.
关键词： transmission electron microscopy,liquid nitrogen,chromium nitride nanoparticles,density functional theory,laser irradiation,UV-Vis absorption spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - First Principles Investigation into Graphene-PbSe MidWave IR (MWIR) Photodetector Physics
摘要： Polycrystalline PbSe is an established low cost material for mid wave-IR photodetection. In this work, we describe a novel design of PbSe MWIR detector that incorporates a graphene layer resulting in three possible distinct modes of operation, depending on the interface design between the functionalized PbSe and Graphene. Using Density Functional Theory (DFT) based simulations we investigate the chemistry of this interface, in terms of back-bonding as well as van-der Waals force, that give rise to rich behavior that is obtainable from this material stack, promising radical new designs for scaled high performance CMOS integrable MWIR photodetectors.
关键词： Photodetector,Graphene,PbSe,Mid-Wave IR,Density Functional Theory
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Power & Energy Society Innovative Smart Grid Technologies Conference (ISGT) - Washington, DC, USA (2019.2.18-2019.2.21)] 2019 IEEE Power & Energy Society Innovative Smart Grid Technologies Conference (ISGT) - Reliable Photovoltaic Generation Forecasting via Quantile Determination
摘要： The electronic and mechanical properties of monolayer SnP2 are calculated by density functional theory (DFT), showing that monolayer SnP2 is a quasi-direct semiconductor with a moderate bandgap of 1.44 eV. The phonon dispersion, the molecular dynamics and the strain energy reveal that SnP2 is dynamically, thermally and mechanically stable. Further, the bandgap of SnP2 sheet can be effectively adjusted by applying strain. These results open the door for future applications in catalysis and optoelectronics.
关键词： density functional theory,stability,monolayer SnP2,tunable bandgap
更新于2025-09-11 14:15:04
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Chern and Z2 topological insulating phases in perovskite-derived 4d and 5d oxide buckled honeycomb lattices
摘要： Based on density functional theory calculations including a coulomb repulsion parameter U, we explore the topological properties of (LaXo3)2/(LaAlo3)4 (111) with X = 4d and 5d cations. the metastable ferromagnetic phases of Latco3 and Lapto3 with preserved P321 symmetry emerge as Chern insulators (CI) with C = 2 and 1 and band gaps of 41 and 38 meV at the lateral lattice constant of LaAlo3, respectively. Berry curvatures, spin textures as well as edge states provide additional insight into the nature of the ci states. While for X = Tc the CI phase is further stabilized under tensile strain, for X = Pd and Pt a site disproportionation takes place when increasing the lateral lattice constant from aLAo to aLno. the ci phase of X = Pt shows a strong dependence on the Hubbard U parameter with sign reversal for higher values associated with the change of band gap opening mechanism. Parallels to the previously studied (X2o3)1/(Al2o3)5 (0001) honeycomb corundum layers are discussed. Additionally, non-magnetic systems with X = Mo and W are identified as potential candidates for Z2 topological insulators at aLAo with band gaps of 26 and 60 meV, respectively. The computed edge states and Z2 invariants underpin the non-trivial topological properties.
关键词： density functional theory,perovskite-derived oxides,Chern insulators,Z2 topological insulators,honeycomb lattices
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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quantum dots: Insights from time-dependent density functional theory
摘要： Colloidal quantum dots (QDs) of group III-V are considered as promising candidates for next-generation environmentally friendly light emitting devices, yet there appears to be only limited understanding of the underlying electronic and excitonic properties. Using large-scale density functional theory with the hybrid B3LYP functional solving the single-particle states and time-dependent density functional theory accounting for the many-body excitonic effects, we have identified the structural, electronic, and excitonic optical properties of InP, GaP, and GaInP QDs containing up to a thousand atoms or more. The calculated optical gap of InP QD appears in excellent agreement with available experiments, and it scales nearly linearly with the inverse diameter. The radiative exciton decay lifetime is found to increase surprisingly linearly with increasing the dot size. For GaP QDs we predict an unusual electronic state crossover at a diameter of around 1.5 nm, whereby the nature of the lowest unoccupied molecular orbital (LUMO) state switches its symmetry from (cid:2)5-like at a larger diameter to (cid:2)1-like at a smaller diameter. After the crossover, the absorption intensity of the band-edge exciton states is significantly enhanced. Finally, we find that Vegard’s law holds very well for GaInP random alloyed quantum dots down to ultrasmall sizes with less than a hundred atoms. The obtained energy gap bowing parameter of this common-cation compound in QD regime appears positive, size-dependent, and much smaller than its bulk parentage. The volume deformation, dominating over the charge exchange and structure relaxation effects, is mainly responsible for the QD energy gap bowing. The impact of excitonic effects on the optical bowing is found to be marginal. The present work provides a road map for a variety of electronic and optical properties of colloidal QDs in group III-V that can guide spectroscopic studies.
关键词： InP,excitonic properties,time-dependent density functional theory,GaInP,quantum dots,GaP
更新于2025-09-11 14:15:04
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Transparent Conductive Films Derived from Single-Walled Aluminosilicate Nanotubes
摘要： This study reports on an approach to enhancing the performance of silver nanowire (AgNW)-based transparent conducing films (TCFs) via introducing an emerging class of nanotubes, aluminosilicate nanotubes (AlSiNTs), which can reduce silver ions to form silver nanoparticles (AgNPs). This reaction was carried out in a suspension of AlSiNTs and AgNO3(aq) under ambient conditions, i.e., without the need for additional reducing agents. The results of material characterization suggest that the AlSiNTs collapse after the formation of AgNPs. Computation based on density functional theory (DFT) was used to gain insight into the reducing capability of AlSiNTs. The computational results suggest that octahedral aluminum plays a key role in the transfer of charge from AlSiNTs to adsorbed silver ions. A solution of AlSiNT-AgNP was mixed with a commercial AgNW suspension and deposited on a flexible PET substrate to form TCFs. The addition of AlSiNT-AgNP was shown to improve the connectivity of AgNWs and thus enhance the overall transparency as well as the conductivity of the TCFs. In fact, the TCFs proposed in this work outperform most existing metal oxides- or AgNW-based TCFs.
关键词： aluminosilicate nanotube,transparent conducing film,flexible TCF,imogolite,density functional theory
更新于2025-09-11 14:15:04
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Ambipolar and Robust WSe <sub/>2</sub> Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides
摘要： Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p-type contacts for transition metal dichalcogenides. Here, ambipolar field-effect transistors (FETs) enabled by bilayer WSe2 with self-assembled TMOs (WO2.57) as contacts are reported. Systematic material characterizations demonstrate the formation of WO2.57/WSe2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air-exposure, while pristine properties of WSe2 almost sustain in inner domains. As-fabricated FETs exhibit both polarities, implying WO2.57 with lowered WF at edges can serve as both the p-type and n-type contact for inner WSe2. Noteworthy, greatly reduced contact resistance and enhanced channel current are achieved, compared to the devices without WO2.57 contacts. Linear drain–source current relationship from 77 to 300 K indicates the ohmic contact between edge WO2.57 and inner WSe2. Density functional theory calculations further reveal that the WO2.57/WSe2 heterojunction forms a barrier-less charge distribution. These nm-scale FETs possess remarkable electrical conductivity up to ≈2600 S m?1, ultra-low leakage current down to ≈10?12 A, robustness for high voltage operation, and air stability, which even outperform pristine WSe2 FETs. Theoretical calculations reveal that the high conductivity is exclusively attributed to the air-induced WO2.57 and its further carrier injection to WSe2.
关键词： field-effect transistors,self-passivation,WOx,density functional theory,WSe2
更新于2025-09-11 14:15:04