Calculations on the Size Effects of Raman Intensities of Silicon Quantum Dots

Raman intensities of Si quantum dots (QDs) with up to 11,489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QDs, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QDs are discussed in detail based on these calculations. The calculations are compared with the available experimental observation. We are expecting that our calculations can further stimulate more experimental measurements.Comment: 21 pages, 7 figure

Integer quantum Hall effect and topological phase transitions in silicene

We numerically investigate the effects of disorder on the quantum Hall effect (QHE) and the quantum phase transitions in silicene based on a lattice model. It is shown that for a clean sample, silicene exhibits an unconventional QHE near the band center, with plateaus developing at $\nu=0,\pm2,\pm6,\ldots,$ and a conventional QHE near the band edges. In the presence of disorder, the Hall plateaus can be destroyed through the float-up of extended levels toward the band center, in which higher plateaus disappear first. However, the center $\nu=0$ Hall plateau is more sensitive to disorder and disappears at a relatively weak disorder strength. Moreover, the combination of an electric field and the intrinsic spin-orbit interaction (SOI) can lead to quantum phase transitions from a topological insulator to a band insulator at the charge neutrality point (CNP), accompanied by additional quantum Hall conductivity plateaus.Comment: 7 pages, 4 figure

Plasmon assisted transmission of high dimensional orbital angular momentum entangled state

We present an experimental evidence that high dimensional orbital angular momentum entanglement of a pair of photons can be survived after a photon-plasmon-photon conversion. The information of spatial modes can be coherently transmitted by surface plasmons. This experiment primarily studies the high dimensional entangled systems based on surface plasmon with subwavelength structures. It maybe useful in the investigation of spatial mode properties of surface plasmon assisted transmission through subwavelength hole arrays.Comment: 7 pages,6 figure

Fast Shocks From Magnetic Reconnection Outflows

Magnetic reconnection is commonly perceived to drive flow and particle acceleration in flares of solar, stellar, and astrophysical disk coronae but the relative roles of different acceleration mecha- nisms in a given reconnection environment are not well understood. We show via direct numerical simulations that reconnection outflows produce weak fast shocks, when conditions for fast recon- nection are met and the outflows encounter an obstacle. The associated compression ratios lead to a Fermi acceleration particle spectrum that is significantly steeper than the strong fast shocks commonly studied, but consistent with the demands of solar flares. While this is not the only acceleration mechanism operating in a reconnection environment, it is plausibly a ubiquitous one

Photonic quasicrystal nanopatterned silicon thin film for photovoltaic applications

In this paper, the authors numerically studied the optical properties of a silicon photonic quasicrystal (PQC) nanohole array for photovoltaic applications. With the same active layer thickness, the ultimate efficiency of a solar cell integrated with an optimized PQC nanohole array can be enhanced by 9.01% and 1.40% compared to that with an ordered square lattice of a nanohole array and a random nanohole array, respectively. The absorptance enhancement is mainly due to the higher-order rotational symmetry in PQC structures, which leads to the presence of additional resonant modes, the broadening of existing modes and the reduction of surface reflectance. The angular response for both transverse-electric and transverse-magnetic modes are also analyzed in detail