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Beyond the molecular movie: Dynamics of bands and bonds during a photoinduced phase transition
摘要： Ultrafast nonequilibrium dynamics offer a route to study the microscopic interactions that govern macroscopic behavior. In particular, photoinduced phase transitions (PIPTs) in solids provide a test case for how forces, and the resulting atomic motion along a reaction coordinate, originate from a nonequilibrium population of excited electronic states. Using femtosecond photoemission, we obtain access to the transient electronic structure during an ultrafast PIPT in a model system: indium nanowires on a silicon(111) surface. We uncover a detailed reaction pathway, allowing a direct comparison with the dynamics predicted by ab initio simulations. This further reveals the crucial role played by localized photoholes in shaping the potential energy landscape and enables a combined momentum- and real-space description of PIPTs, including the ultrafast formation of chemical bonds.
关键词： Silicon surface,Photoinduced phase transitions,Chemical bonds,Electronic structure,Indium nanowires,Femtosecond photoemission,Ultrafast dynamics
更新于2025-09-10 09:29:36
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Br-doped Bi2O2CO3 nanosheets with improved electronic structure and accelerated charge migration for outstanding photocatalytic behavior
摘要： The work presents a combinative merit of non-metal ion doping and active facet effect of Bi2O2CO3 photocatalyst. Br-doped Bi2O2CO3 nanosheets with exposed {001} facets were facilely prepared via a one-step hydrothermal reaction with the assistance of cetyltrimethylammonium bromide (CTAB) at a mild temperature of 60 °C for 4 h. The presence of CTAB not only influences the growth of Bi2O2CO3 crystalline but also leads to a Br-doping. Based on the crystal structure and DFT calculation, bromine from CTAB as dopant interstitially incorporates into Bi2O2CO3 lattice, which alters the band gap positions of Bi2O2CO3 and generates delocalized impurity states at the Fermi level. The improved electronic structure endows Br-doped Bi2O2CO3 with a broadened light-harvesting and accelarated charge migration. In addition, the thin nanosheet means more exposure of {001} active facets and larger internal electric field, which would also benefit for the charge separation. The sample with a trace Br content of 1.17 wt% shows the best degradation efficiency for RhB with a rate constant k enhanced by 3.6 folds compared with that of pure Bi2O2CO3 under simulated solar irradiation. Combining the effective catalytic sites and the detected active species, a possible migration mechanism of photogenerated e-/h+ pairs on the surface of Br-doped Bi2O2CO3 nanosheet is proposed. The work provides some new insights into the rational design and synthesis of non-metal doped semiconductor photocatalyst with facet dependency.
关键词： electronic structure,Br-doping,Bi2O2CO3,photocatalysis,facet effect,charge migration
更新于2025-09-10 09:29:36
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Ferromagnetism induced by vacancies in (N, Al)-codoped 6H-SiC
摘要： The electronic structures and magnetic properties of 6H-SiC doped with N, C vacancies (VC), Si vacancies (VSi) and Al are studied by first principles calculations. The results indicate that the N substituting C in 6H-SiC cannot order magnetism but VSi can introduce magnetic moments effectively. Ferromagnetism coupling is obtained in (N, 2VSi)-codoped 6H-SiC. The ferromagnetism can be mainly attributed to the interactions between the 2p orbitals of C atoms around Si vacancies. More interestingly, substituting Si with Al can enhance the ferromagnetic states in 6H-SiC. We also studied the effect of charge on magnetic properties and provide an effective method of tuning magnetism in 6H-SiC.
关键词： First principles,Electronic structure,Dilute magnetic semiconductors,6H-SiC,Magnetic properties
更新于2025-09-10 09:29:36
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Electronic and Geometric Structure, Optical Properties, and Excited State Behavior in Atomically Precise Thiolate-Stabilized Noble Metal Nanoclusters
摘要： Ligand-protected noble metal nanoclusters are of interest for their potential applications in areas such as bioimaging, catalysis, photocatalysis, and solar energy harvesting. These nanoclusters can be prepared with atomic precision, which means that the properties of these nanoclusters can vary significantly depending on the exact stoichiometry and geometric structure of the system. This leads to important questions such as: What are the general principles that underlie the physical properties of these nanoclusters? Do these principles hold for all systems? What properties can be “tuned” by varying the size and composition of the system? In this Account, we describe research that has been performed to analyze the electronic structure, linear optical absorption, and excited state dynamics of thiolate-stabilized noble metal nanoclusters. We focus primarily on two systems, Au25(SR)18? and Au38(SR)24, as models for understanding the principles underlying the electronic structure, optical properties, luminescence, and transient absorption in these systems. In these nanoclusters, the orbitals near the HOMO?LUMO gap primarily arise from atomic 6sp orbitals located on Au atoms in the gold core. The resulting nanocluster orbitals are delocalized throughout the core of these systems. Below the core-based orbitals lies a set of orbitals that are primarily composed of Au 5d and S 3p atomic orbitals from atoms located around the exterior gold?thiolate oligomer motifs. This set of orbitals has a higher density of states than the set arising from the core 6sp orbitals. Optical absorption peaks in the near-infrared and visible regions of the absorption spectrum arise from excitations between core orbitals (lowest energy peaks) and excitations from oligomer-based orbitals to core-based orbitals (higher energy peaks). Nanoclusters with different stoichiometries have varying gaps between the core orbitals themselves as well as between the band of oligomer-based orbitals and the band of core orbitals. These gaps can slow down nonradiative electron transfer between excited states that have different character; the excited state electron and hole dynamics depend on these gaps. Nanoclusters with different stoichiometries also exhibit different luminescence properties. Depending on factors that may include the symmetry of the system and the rigidity of the core, the nanocluster can undergo large or small nuclear changes upon photoexcitation, which affects the observed Stokes shift in these systems. This dependence on stoichiometry and composition suggests that the size and the corresponding geometry of the nanocluster is an important variable that can be used to tune the properties of interest. How does doping affect these principles? Replacement of gold atoms with silver atoms changes the energetics of the sp and d atomic orbitals that make up the nanocluster orbitals. Silver atoms have higher energy sp orbitals, and the resulting nanocluster orbitals are shifted in energy as well. This affects the HOMO?LUMO gap, the oscillator strength for transitions, the spacings between the different bands of orbitals, and, as a consequence, the Stokes shift and excited state dynamics of these systems. This suggests that nanocluster doping is one way to control and tune properties for use in potential applications.
关键词： ligand-protected noble metal nanoclusters,doping,electronic structure,optical properties,transient absorption,luminescence,atomic precision
更新于2025-09-10 09:29:36
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Modified Becke–Johnson (mBJ) exchange potential investigations of the structural and optoelectronic properties of BaThO3 in cubic and orthorhombic phase
摘要： The all electrons full potential linearized augmented plane waves (FP-LAPW) method with GGA, LDA and mBJ approximation is used to study BaThO3 perovskite in cubic and orthorhombic phases. The structural parameters are found consistent with the experimental results. The electronic band structures and density of states demonstrate that BaThO3 is a wide band gap insulator in both phases. Furthermore, the optical properties demonstrate that the optical gap of the material is 5.8 eV, which lies in the UV region of the electromagnetic spectrum and hence the compound can be used in optoelectronic devices.
关键词： Electronic structure,Optical properties,FP-LAPW,mBJ,Perovskite
更新于2025-09-10 09:29:36
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The effect of chalcogen and metal on the electronic properties and stability of metal–chalcogenides clusters, TM6Xn(PH3)6 (TM = Mo, Cr, Re, Co, Ni; X = Se, Te; n = 8,5)
摘要： We have performed a comparative study of the electronic structure, stability, and magnetic properties of a series of metal–chalcogen clusters stabilized by PH3 ligands. Clusters studied include TM6X8(PH3)6, TM = Cr, Mo, Re, Co, X = Se, Te, and Ni6X(PH3)6, X = Se, and Te. We find that the phosphine ligands act as charge donors, transferring charge to the metal sites, creating an electrostatic effect that lowers the ionization energy. The electronic structure of the cluster also has a significant effect on its charge donor properties, as the Re cluster has a closed electronic shell with a charge state of +2, making it an alkaline earth superatom. The chromium clusters are found to have a series of close lying magnetic isomers. Selenium is a better charge acceptor than tellurium and this causes the telluride clusters to have lower ionization potentials, while the enhanced charge transfer to selenium increases the binding energy of the phosphine ligand.
关键词： metal–chalcogen clusters,PH3 ligands,ionization energy,superatom,stability,charge transfer,magnetic properties,electronic structure
更新于2025-09-10 09:29:36
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First principle calculations of electronic, band structural, and optical properties of BixSr1-xTiO3 perovskite
摘要： Based on the first-principles plane-wave ultrasoft pseudopotential method, we set up models of perovskite-type oxides BixSr1-xTiO3 (x=0, 0.25, 0.5, 0.625, 1), and the geomertry optimization, the electronic and band structure were studied. The calculation results show that the binding energy decreases in BixSr1-xTiO3 after Sr2+ replaced by Bi3+. The calculations of the band structure show that BixBa1-xTiO3 are direct band gap semiconductors. The partial substitution of Bi3+ ions can increase the band gap and the absorption spectra ranges shift blue, and the values of band gaps are in the order of Bi0.625Sr0.375TiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3>BiTiO3, and the absorption spectrum becomes wider in the order of Bi0.625Sr0.375TiO3>BiTiO3>Bi0.5Sr0.5TiO3>Bi0.25Sr0.75TiO3>SrTiO3. Based on the density of states, the top of the valence band is hybridized by O-2p and Sr-5s and the bottom of the conduction band state is mainly constituted by the Ti-3d state and Bi-6p. The regulation of photo-catalytic activity of the perovskite SrTiO3 can be realized by Bi ions substituting for Sr ions, and Bi-based perovskite BiTiO3 will be a potential photocatalytic material.
关键词： band gap,electronic structure,density of states,absorption spectra,BixSr1-xTiO3
更新于2025-09-10 09:29:36
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Stone-Wales like defects formation, stability and reactivity in black phosphorene
摘要： During the synthesis of ultra-thin materials with a hexagonal lattice structure, Stone-Wales (SW) type of defects are quite likely to be formed that can result in dramatic changes in their electronic and mechanical properties. Here we investigated the formation and reactivity of SW-like defects in Phosphorene. Our calculations show that the energy barrier for the formation of SW-like defects in phosphorene is significantly lower than in graphene. Moreover, the nature of phosphorene provides a large energy barrier for the healing of the SWL defect, therefore defective phosphorene is stable. SWL-defect phosphorene are semiconductors with bandgap wider than pristine phosphorene that depends on the density of defects. Furthermore, nitrogen substitution in SWL defected phosphorene shows that defect lattice sites are the least preferable substitution locations for the N atoms. Easy formation of SWL defects in phosphorene provides a guideline for bandgap engineering in phosphorene based materials through such defects.
关键词： Dopant,Electronic Structure,Phosphorene,Nitrogen,Stone-Wales-like defects
更新于2025-09-10 09:29:36
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Photophysical and photocatalytic properties of corrophyll and chlorophyll
摘要： Tetrapyrrolic macrocycles are well known photosensitizers, absorbing light in the ultraviolet and visible region. The quantum e?ciency of these naturally occurring compounds in optical processes, and the possibility of altering their behavior by modifying its constituent features, make them promising candidates for applications as Dye Sensitized Solar Cells (DSSC) and photocatalytic reactions. The time-dependent density-functional theory (TD-DFT) were used to study the optical and redox properties of chlorophyll and corrin-related molecules (corrophyll). The in?uence of the substituents and metallic atoms in their properties have been investigated. Our results show lower reduction potentials for corrophyll molecules compared with chlorophyll. The optical absorbance spectra of corrophyll without a metallic atom at their central rings shows a signi?cant blue-shift, as compared to their chlorophyll counterparts. The presence of Co(I) ion species at the corrophyll core leads to oxidation potentials below than that of water, which puts corrophyll ahead of traditional chlorophyll pigments as photocatalysts. We show that the substituents and the ions coordinated to the macrocycles play an important role in this phenomena. These ?ndings show the great potential of tuning the spectroscopic and reactive properties of tetrapyrrole macrocycles for applications in photocatalysis and optoelectronic devices, while keeping their essential structural features intact.
关键词： Corrole,Photophysics,Porphyrin,Electronic structure,TD-DFT,Optical absorbance,Photocatalysis
更新于2025-09-10 09:29:36
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European Microscopy Congress 2016: Proceedings || Is the electronic structure of few layer transition metal dichalcogenides always two dimensional ?
摘要： The electronic structure of the transition metal dichalcogenides (TMDs) is investigated using angle-resolved photoemission spectroscopy (ARPES). We observe a new class of layered materials that can be prepared in various thicknesses down to single layers. Compared with the more well-known graphene, the TMDs are semiconductors and can be more useful in applications where an energy gap is essential. Our results show that the electronic structure of the TMDs is highly dependent on the number of layers, with a transition from indirect to direct bandgap as the thickness is reduced to a single layer. This transition is accompanied by a significant enhancement in photoluminescence intensity, making monolayer TMDs promising candidates for optoelectronic applications.
关键词： Angle-resolved photoemission spectroscopy,Bandgap engineering,Electronic structure,Optoelectronic applications,Transition metal dichalcogenides
更新于2025-09-10 09:29:36