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Visualizing Elementary Reactions of Methanol by Electrons and Holes on TiO2(110) Surface
摘要： Direct visualization and comparison of the elementary reactions induced by electrons and holes are of importance for finding a way to conduct chemical reactions and reaction sequences in a controllable manner. As a semiconductor, TiO2 provides a playground to perform the measurements, and more, the information can be useful for design of high performance TiO2-based catalysts and photocatalysts. Here, we present our investigation on the elementary reactions of CH3OH on TiO2 surface through visualization of specific elementary steps by highly controllable electron- and hole-injection using scanning tunneling microscopy. The distinct sequential routes and their kinetics, namely breaking C-O and O-H bonds by electrons and breaking O-H and C-H bonds by holes, respectively, have been experimentally identified and well elucidated by density functional theory calculations. Our nonlocal h-injection experimental and theoretical results suggest that the delocalized holes in the TiO2 substrate should be responsible for the temperature-dependent h-route reactions. The locally triggered e-route reaction is associated with the fact that the location of the unoccupied hybridization states is much higher than the conduction band onset. Our findings resolve the long standing debate about the intermediate species and reaction mechanism in photocatalytic oxidation of CH3OH. Our proposed protocol offers a powerful means to study elementary reactions induced by electrons and holes on semiconductor surface in general.
关键词： scanning tunneling microscopy,elementary reactions,density functional theory,CH3OH,holes,TiO2,electrons
更新于2025-09-23 15:21:01
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Crystal structure and ferroelectric polarization of tetragonal (Bi <sub/>1/2</sub> Na <sub/>1/2</sub> )TiO <sub/>3</sub> –12BaTiO <sub/>3</sub>
摘要： We have investigated the crystal structure and ferroelectric polarization of (Bi1/2Na1/2)TiO3–12%BaTiO3 by high-resolution neutron powder di?raction Rietveld analysis and density-functional theory calculations. It is revealed that the sample has a ferroelectric distortion in tetragonal P4mm symmetry along with a large tetragonality c/a of 1.022. The A- and B-site atoms exhibit a cooperative o?-center displacement along the polar c-axis, which results in a large spontaneous polarization of 54 μC/cm2.
关键词： crystal structure,neutron powder diffraction,tetragonal (Bi1/2Na1/2)TiO3–12BaTiO3,density-functional theory,ferroelectric polarization
更新于2025-09-23 15:21:01
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Terahertz Spectral of Enantiomers and Racemic Amino Acids by Time-Domain-Spectroscopy Technology
摘要： The absorption spectra of four amino acids were studied. These spectra are obtained by terahertz time-domain spectroscopy (TDS) technique. The four amino acids are alanine, methionine, leucine, and valine, respectively. The spectra of their enantiomers (L-, D-) and racemic compounds (DL-) were investigated. Although the two isomers have very similar structures, their absorption spectra are obviously different. The absorption coefficient of each structure is calculated by the density functional theory (DFT), and the simulated spectra of each structure are obtained. It is shown that the number of the calculated peaks is in good agreement with the experimental ones. The experimental spectra were compared with the theoretical spectra. The differences between the absorption spectra of isomers are presented, and the reasons for the differences were analyzed. The vibratory spectra of biomolecules were studied, and the correlation between molecular structure and function was further understood.
关键词： collective vibration,isomers,amino acids,density functional theory,terahertz time-domain spectroscopy
更新于2025-09-23 15:21:01
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Prediction of a Dynamically Stable New Half-Metallic Phase for the BaN and BaC Compounds
摘要： The structural, magnetic, elastic, mechanical, and thermodynamic properties of BaC and BaN compounds in different phases were studied using first-principle calculations based on spin-polarized density functional theory within the generalized gradient approximation (GGA-PBEsol) and the modified Becke–Johnson approach (mBJ-GGA-PBEsol) for the exchange-correlation energy and potential. The following phases—rock-salt (NaCl), CsCl, zinc blende (ZB), NiAs- and WZ-type hexagonal, tetragonal (P4/nmm), and orthorombic (Pnma) phases of BaC and BaN compounds—were considered. We obtained that Pnma phase has the lowest energy configuration as a function of the volume for both the BaN and BaC compounds. The ferromagnetic phase is energetically favored with respect to the non-magnetic phase in the BaN and BaC compounds, except for the CsCl phase in the BaC compound. Considering the phonon dynamics of BaN and BaC compounds in the Pnma, NaCl, ZB, and WZ phases, we observed that the BaN and BaC compounds in the Pnma, NaCl, and ZB phases are dynamically stable. The calculated elastic properties for the Pnma, NaCl, and ZB phases show that they are elastically stable. The Pnma phase for the BaN and BaC compounds, which is a new phase was found to be dynamically and elastically stable. The BaN and BaC compounds exhibit half-metallic behavior in the Pnma, NaCl, and ZB phases. The half-metallic and magnetic character found in the BaN and BaC compounds are attributed to the presence of spin-polarized 2p orbitals of the nitrogen and carbon atoms, respectively. We found that BaN and BaC compounds are half-metallic ferromagnets with magnetic moment of 1 μB and 2 μB per formula unit, respectively. Using the GGA-PBEsol (mBJ-GGA-PBEsol) approach, our calculated half-metallic gaps for BaN and BaC compounds are 0.22 eV (0.54 eV) and 0.32 eV (0.44 eV) in the Pnma phase, 0.23 eV (1.32 eV) and 0.35 eV (1.00 eV) in the NaCl phase, and 0.38 eV (1.54 eV) and 0.50 eV (1.57 eV) in the ZB phase, respectively.
关键词： BaN,Density functional theory,Half-metallic,BaC,Phase stability,Phonon dynamics
更新于2025-09-23 15:21:01
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Cyclic versus straight chain oligofuran as sensor: A detailed DFT study
摘要： This study is a novel approach for exploring the sensitivity and selectivity of cyclic oligofuran (5/6/7CF) toward gaseous analytes and their comparison with straight chain analogues (5/6/7SF). The work is not only vital to understand the superior sensitivity but also for rational design of new sensors based on cyclic ring structures of oligofuran. Interaction of cyclic and straight chain oligofuran with NH3, CO, CO2, N2H4, HCN, H2O2, H2S, CH4, CH3OH, SO2, SO3 and H2O analytes is studied via DFT calculation at B3LYP-D3/6-31++G (d, p) level of theory. The sensitivity and selectivity are illustrated by the energetic parameters (Ebind, SAPT0 energies, NCI analysis) electronic properties (H-L gap, percentage of average energy gap, CHELPG charge transfer, DOS spectra) and UV-Vis analysis. All these properties are simulated at B3LYP/6-31G (d) level of theory while UV-Vis is calculated at TD-DFT method. Cyclic oligofuran has high binding energy with analytes compared to 5/6/7SF which corresponds the higher sensitivity of 5/6/7CF. Furthermore, the cyclization of oligofuran significantly improve the sensitivity and selectivity of the system. Alteration in electronic properties of 5/6/7CF and 5/6/7SF is remarkably high upon complexation with SO2 and SO3. Further the stability of rings (5, 6 and 7 membered cyclic oligofurans) and their SO3 complexes is also confirmed by molecular dynamics calculations. The finding of the work clearly suggests that the cyclic geometry enhances not only sensitivity but also selectivity of conducting polymers (oligofuran).
关键词： Oligofuran,Noncovalent interaction index (NCI),Density Functional Theory (DFT),CHELPG charge transfer,Symmetry adopted perturbation theory (SAPT)
更新于2025-09-23 15:19:57
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Discovery of Novel Two-Dimensional Photovoltaic Materials Accelerated by Machine Learning
摘要： Searching for novel, high-performance, two-dimensional photovoltaic (2DPV) materials is an important pursuit for solar cell applications. In this work, an efficient method based on the machine learning algorithm combined with high-throughput screening is developed. Twenty-six 2DPV candidates are successfully ruled out from 187093 experimentally identified inorganic crystal structures, whose conversion efficiencies are predicted by density functional theory calculations. Our results indicate that Sb2Se2Te, Sb2Te3, and Bi2Se3 exhibit conversion efficiencies that are much higher than those of others, which make them promising 2DPV candidates for further applications. The superior photovoltaic performance is then analyzed, and the hidden structure-related relationships with photovoltaic properties are established, thus providing important information for the further examination of 2DPV materials. Given the rapid development of the database of materials, this approach not only provides an efficient way of searching for novel 2DPV materials but also can be applied to exploration of a broad range of functional materials.
关键词： high-throughput screening,machine learning,solar cell applications,density functional theory,two-dimensional photovoltaic materials
更新于2025-09-23 15:19:57
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Strain engineering of ferroelectric KNbO <sub/>3</sub> for bulk photovoltaic applications: an insight from density functional theory calculations
摘要： A large ferroelectric (FE) polarization and low bandgap are essential to improving the bulk photovoltaic response which is the generation of photocurrent in the polar non-centrosymmetric materials such as FE perovskite oxides. Among various perovskite oxides, Potassium Niobate (KNbO3, KNO) is a promising FE material for bulk photovoltaic applications as its bandgap and polarization can be tuned effectively by strain, doping, or by applying an electric field. In this work, using the density functional theory calculations, we present an insight into the strain engineering of polarization, band structure, and optical properties of the cubic (C), tetragonal (T), and orthorhombic (O) structures of KNO. The tensile and compressive strain under the triaxial, biaxial, and uniaxial conditions are applied along the direction parallel and perpendicular to the polar axis of KNO structures. We find that the bandgap decreases along with a substantial increment of polarization on the application of tensile strain along the direction parallel to the polar axis. In T (O) phase at +2% strain, the polarization increases by 18 μC cm?2 (14 μC cm?2) in triaxial, 26 μC cm?2 (16 μC cm?2) in biaxial, and 29 μC cm?2 (29 μC cm?2) in uniaxial conditions with a considerable decreasing of bandgap with respect to zero strain condition. Therefore, wisely applying the tensile strain along the direction parallel to the polar axis, the photovoltaic efficiency of KNO can be improved.
关键词： density functional theory,bulk-photovoltaic,band gap,strain,polarization
更新于2025-09-23 15:19:57
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Layer-dependent signatures for exciton dynamics in monolayer and multilayer WSe2 revealed by fluorescence lifetime imaging measurement
摘要： Two-dimensional (2D) transition-metal dichalcogenide (TMD) materials have aroused noticeable interest due to their distinguished electronic and optical properties. However, little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices. The process of fluorescence can well reveal the process of exciton transition after excitation. In this work, the room-temperature layer-dependent exciton dynamics properties in layered WSe2 are investigated by the fluorescence lifetime imaging microscopy (FLIM) for the first time. This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions. Compared with the lifetime of neutral excitons (< 0.3 ns within four-layer), trions possess a longer lifetime (~ 6.6 ns within four-layer) which increases with the number of layers. We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe2. Besides, the whole average lifetime increases over 10% when WSe2 flakes added up from monolayer to four-layer. This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature, enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.
关键词： two-dimensional (2D) WSe2,fluorescence lifetime,fluorescence lifetime imaging microscopy (FLIM),exciton dynamics,density functional theory (DFT)
更新于2025-09-23 15:19:57
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Polar coupling enabled nonlinear optical filtering at MoS2/ferroelectric heterointerfaces
摘要： Complex oxide heterointerfaces and van der Waals heterostructures present two versatile intrinsically different platforms for exploring emergent quantum phenomena and designing new functionalities. The rich opportunity offered by the synergy between these two classes of materials, however, is yet to be charted. Here, we report an unconventional nonlinear optical filtering effect resulting from the interfacial polar alignment between monolayer MoS2 and a neighboring ferroelectric oxide thin film. The second harmonic generation response at the heterointerface is either substantially enhanced or almost entirely quenched by an underlying ferroelectric domain wall depending on its chirality, and can be further tailored by the polar domains. Unlike the extensively studied coupling mechanisms driven by charge, spin, and lattice, the interfacial tailoring effect is solely mediated by the polar symmetry, as well explained via our density functional theory calculations, pointing to a new material strategy for the functional design of nanoscale reconfigurable optical applications.
关键词： nonlinear optical filtering,second harmonic generation,MoS2/ferroelectric heterointerfaces,density functional theory,polar symmetry
更新于2025-09-23 15:19:57
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Multilayer plasmonic photonic structures embedding photochromic molecules or optical gain molecules
摘要： We study the optical properties of different functional molecular systems in order to embed them in properly designed photonic structures for photochromic switching and lasing. We study the light absorption of two photochromic molecules and of 4,4’-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) with density functional theory. For the photochromic diarylethene we derivate the refractive index with Kramers-Kronig relations and we design multilayer photonic structures alternating diarylethene with either poly vinyl carbazole or fluorine indium co-doped cadmium oxide (FICO) nanoparticle-based layers. For BSB-Cz we design a one-dimensional photonic crystal alternating BSB-Cz layers wit SiO2 layers and a microcavity embedding BSB-Cz between indium tin oxide (ITO) / FICO nanoparticle-based multilayers.
关键词： multilayer plasmonic photonic structures,photochromic molecules,density functional theory,Kramers-Kronig relations,optical gain molecules
更新于2025-09-23 15:19:57