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Plasmonic nanoclusters can strongly absorb light energy and generate hot carriers, which have great potentials in photovoltaic and photocatalytic applications. A vital step for those plasmonic applications is the charge transfer at the metal–semiconductor interface. The effect of the light polarization on the charge transfer has not been theoretically investigated so far. Here, we take the Ag–TiO2 system as a model system to study the polarization effect using time-dependent density functional theory simulations. We find that the charge transfer is sensitive to the light polarization, which has its origin in the polarization-dependent hot carrier distributions. For the linearly polarized light, it shows a sine-square dependence on the polar angle, indicating that the charge transfer response to the linear polarization can be decomposed into components perpendicular and parallel to the interface. We also find that there exists directional charge transfer with a circular light polarization. Our results demonstrate that the light polarization can significantly affect the charge transfer behavior and, thus, offer a new degree of freedom to manipulate the plasmonic applications. [ABSTRACT FROM AUTHOR]

Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF 2 single layer and its heterostructures with monolayer MoS 2 are investigated from first-principles calculations. V Ca introduces a shallow defect level close to the VBM, whereas V F introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, V F has a relatively lower formation energy than V Ca , except for the extreme Ca-rich case. Thus, V F should be dominant in CaF 2. The band offset between CaF 2 and MoS 2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF 2 , the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF 2 to MoS 2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS 2 , and the electronic properties of MoS 2 are almost intact. Compared with h -BN that has a small valence band offset with MoS 2 and could introduce in-gap defect states, CaF 2 can be a good candidate to serve as the dielectric layer of MoS 2 -based transistors. [ABSTRACT FROM AUTHOR]

A semiclassical model is developed to describe plasmon-electron coupling and electronic damping of surface plasmons. It is compared with the ab initio linear response calculations for metallic thin films in the jellium approximation and for a realistic crystalline Mg(0001) surface. The semiclassical model is able to reproduce the quantum oscillations of plasmon linewidth, which was obtained in the previous ab initio calculations. In addition, state-resolved analysis reveals the origin of these oscillations, which result from superposition of the short-period oscillations of individual electron-hole pair transitions. The semiclassical model is further applied to a crystalline Mg(0001) surface, where linewidth dispersion of the surface plasmon is calculated and shows good agreement with earlier ab initio calculation and experiment. Our results suggest that this semiclassical approach is quite promising for the quantitative description of plasmon-electron coupling and associated processes such as surface-enhanced Raman scattering, light emission, and fluorescence. [ABSTRACT FROM AUTHOR]

The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics. [ABSTRACT FROM AUTHOR]

We study the hydration shell formation of alkali metal ions at a graphite surface. Two-dimensional shell structures are found in the initial stage of hydration, in contrast to the three-dimensional structures in bulk water and clusters. Comparison of vibrational spectra with experiments identifies the shell structures and the thermally induced transition from the first to the second shell. We also found intriguing competition between hydration and ion–surface interaction, leading to different solvation dynamics between K and Na. Implications of these results in ionic processes at interfaces are elaborated. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Exploring gate insulator materials for 2D transistors and their defect properties is of importance for device performance optimization. In this work, the structural and electronic properties of intrinsic vacancies in the CaF 2 single layer and its heterostructures with monolayer MoS 2 are investigated from first-principles calculations. V Ca introduces a shallow defect level close to the VBM, whereas V F introduces a deep level below the CBM. In both cases, spin polarization is observed. Overall, V F has a relatively lower formation energy than V Ca , except for the extreme Ca-rich case. Thus, V F should be dominant in CaF 2. The band offset between CaF 2 and MoS 2 is determined to be type-I, with large offsets at both the conduction band and valence band. With the presence of vacancies in CaF 2 , the type-I band offset is preserved. The electron or hole on the defect states will transfer from CaF 2 to MoS 2 due to the large band offset, and spin polarization vanishes. Nevertheless, there are no defect states inside the gap or around the band edge of MoS 2 , and the electronic properties of MoS 2 are almost intact. Compared with h -BN that has a small valence band offset with MoS 2 and could introduce in-gap defect states, CaF 2 can be a good candidate to serve as the dielectric layer of MoS 2 -based transistors. [ABSTRACT FROM AUTHOR]

We investigate the dynamical response of a metal nanoparticle and the electron transfer to a molecule near its surface using time-dependent density functional theory. In addition to the linear response of the Mie resonance, double plasmon excitations and a low-frequency charge transfer band emerge and become prominent at high laser intensities. Both modes are nonlinear processes, which are derived from the re-excitation and decay of the primary plasmon mode, respectively. Our results shed light on the localised characters of the plasmon-molecule coupling and hot electron distributions. These findings have general implications to photoinduced phenomena in nanosystems.

Ion hydration at a solid surface ubiquitously exists in nature and plays important roles in many natural processes and technological applications. Aiming at obtaining a microscopic insight into the formation of such systems and interactions therein, we have investigated the hydration of alkali metal ions at a prototype surface-graphite (0001), using first-principles molecular dynamics simulations. At low water coverage, the alkali metal ions form two-dimensional hydration shells accommodating at most four (Li, Na) and three (K, Rb, Cs) waters in the first shell. These two-dimensional shells generally evolve into three-dimensional structures at higher water coverage, due to the competition between hydration and ion-surface interactions. Exceptionally K was found to reside at the graphite-water interface for water coverages up to bulk water limit, where it forms an "umbrellalike" surface hydration shell with an average water-ion-surface angle of 115 degrees . Interactions between the hydrated K and Na ions at the interface have also been studied. Water molecules seem to mediate an effective ion-ion interaction, which favors the aggregation of Na ions but prevents nucleation of K. These results agree with experimental observations in electron energy loss spectroscopy, desorption spectroscopy, and work function measurement. In addition, the sensitive dependence of charge transfer on dynamical structure evolution during the hydration process, implies the necessity to describe surface ion hydration from electronic structure calculations.