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Jiang N.,Chinese University of Hong Kong | Ruan Q.,Chinese University of Hong Kong | Qin F.,Chinese University of Hong Kong | Wang J.,Chinese University of Hong Kong | Lin H.-Q.,Beijing Computational Science Research CenterBeijing
Nanoscale | Year: 2015

Active modulation of the plasmon coupling in homodimers of polyaniline (PANI)-coated Au nanospheres is achieved by changing the proton-doping state of the PANI shell. Such a PANI-enabled modulation of the plasmon coupling in the dimers gives rise to remarkable spectral shifts, which show an exponential dependence on the interparticle gap distance. For the dimer with a 10 nm PANI shell thickness and a 0.5 nm gap distance, the shift of the stronger scattering peak in response to the active modulation reaches 231 nm. Electrodynamic simulations reveal that the shift of the dipolar bonding plasmon mode dominates the position variation of the stronger scattering peak for the dimers with different gap distances. Moreover, the quadrupolar bonding plasmon mode can be turned on and off by controlling the proton-doping state of the dimers with gap distances of less than ∼3 nm. These results are of high importance for fundamentally understanding the sensitivity of coupled plasmon resonance modes to the dielectric environment, as well as for designing active plasmonic devices with high modulation performances. This journal is © The Royal Society of Chemistry. Source

Tang L.,Dalian Nationalities University | Shi R.,Dalian University of Technology | Su Y.,Dalian University of Technology | Zhao J.,Dalian University of Technology | Zhao J.,Beijing Computational Science Research CenterBeijing
Journal of Physical Chemistry A | Year: 2015

In order to understand the cage fusion behavior during the nucleation processes of methane hydrate (MH), methane-encapsulated double-cage clusters (CH4)2(H2O)n (n = 30-43) and several multicage structures with three or more cages were studied employing DFT-D methods. We find that almost all the lowest-energy double-cage structures can be constructed by merging the most stable structures of the monocage clusters CH4(H2O)n (n = 18-24). Double-cage structures can achieve higher stability through sharing a hexagon than a pentagon, which may be applicable to larger fused cage clusters. The preference of hexagons during cage fusion should be favorable for the appearance of the cages including hexagons such as the 51262, 51264 cages during the MH nucleation process. The symmetric C-H stretching modes of methane molecules in the double-cage structures show a clear trend of red shift with increasing size of the composing monocages. Compared with the case of monocages, the stretching frequencies of methane molecules in double-cage structures shift slightly, indicating variation of monocage configuration when cage fusion occurs. The larger multicage structures are found to possess higher fusion energies through sharing more polygons. Their thermodynamic stabilities do not simply increase with the number of fused monocages and are affected by the spatial arrangement of the building cages. © 2015 American Chemical Society. Source

Zhang Y.N.,Chengdu Green Energy And Green Manufacturing Technology | Zhang Y.N.,Beijing Computational Science Research CenterBeijing | Zhang Y.N.,University of California at Irvine | Law M.,University of California at Irvine | Wu R.Q.,University of California at Irvine
Journal of Physical Chemistry C | Year: 2015

Through density functional calculations, we investigated the diffusion of isolated sulfur vacancies (VS) from the bulk of iron pyrite (cubic FeS2) to the (100) and (111) surfaces. The influence of vacancy depth on the vacancy formation energy and the activation energy for vacancy diffusion are discussed. Significantly, we find that VS defects tend to migrate toward stoichiometric and sulfur-rich surfaces through sequential "intra-dimer" and "inter-dimer" hops. We find a pre-exponential constant (D0) of 9 × 10-7 m2 s-1 and an activation energy (E) of 1.95 eV for sulfur vacancy diffusion in bulk pyrite, corresponding to a vacancy diffusion coefficient DV = D0 exp(-E/kT) = 9 × 10-40 m2 s-1 at 25 °C and 5 × 10-18 m2 s-1 at 600 °C. The activation energy is smaller near the surface (e.g., E = 1.5 eV near the stoichiometric (100) surface), resulting in faster vacancy diffusion near the surface than in the bulk. Using the formation enthalpy of VS at the (100) surface, E = 2.37 eV, we find a sulfur diffusivity in bulk pyrite DS = 7 × 10-47 m2 s-1 at 25 °C and 2 × 10-20 m2 s-1 at 600 °C. The calculated DS values are in reasonable agreement with experiment only at intermediate temperatures (∼275-625 °C). Our results show that bulk and near-surface sulfur vacancies can be healed in sulfur-rich conditions at reasonably high temperatures. The mechanism of vacancy diffusion presented here should be useful in managing VS defects during the fabrication of high-quality pyrite samples for solar energy conversion applications. © 2015 American Chemical Society. Source

Seshadreesan K.P.,Louisiana State University | Dowling J.P.,Louisiana State University | Dowling J.P.,Beijing Computational Science Research CenterBeijing | Agarwal G.S.,Oklahoma State University
Physica Scripta | Year: 2015

In continuous-variable quantum information, non-Gaussian entangled states that are obtained from Gaussian entangled states via photon subtraction are known to contain more entanglement. This makes them better resources for quantum information processing protocols, such as, quantum teleportation. We discuss the teleportation of non-Gaussian, non-classical Schrödinger-cat states of light using two-mode squeezed vacuum light that is made non-Gaussian via subtraction of a photon from each of the two modes. We consider the experimentally realizable cat states produced by subtracting a photon from the single-mode squeezed vacuum state. We discuss two figures of merit for the teleportation process, (a) the fidelity, and (b) the maximum negativity of the Wigner function at the output. We elucidate how the non-Gaussian entangled resource lowers the requirements on the amount of squeezing necessary to achieve any given fidelity of teleportation, or to achieve negative values of the Wigner function at the output. © 2015 The Royal Swedish Academy of Sciences. Source

Meng L.,Xiamen University | Yam C.,Beijing Computational Science Research CenterBeijing | Yam C.,University of Hong Kong | Zhang Y.,University of Hong Kong | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2015

The unique optical properties of nanometallic structures can be exploited to confine light at subwavelength scales. This excellent light trapping is critical to improve light absorption efficiency in nanoscale photovoltaic devices. Here, we apply a multiscale quantum mechanics/electromagnetics (QM/EM) method to model the current-voltage characteristics and optical properties of plasmonic nanowire-based solar cells. The QM/EM method features a combination of first-principles quantum mechanical treatment of the photoactive component and classical description of electromagnetic environment. The coupled optical-electrical QM/EM simulations demonstrate a dramatic enhancement for power conversion efficiency of nanowire solar cells due to the surface plasmon effect of nanometallic structures. The improvement is attributed to the enhanced scattering of light into the photoactive layer. We further investigate the optimal configuration of the nanostructured solar cell. Our QM/EM simulation result demonstrates that a further increase of internal quantum efficiency can be achieved by scattering light into the n-doped region of the device. © 2015 American Chemical Society. Source

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