Density matrix based time-dependent density functional theory and the solution of its linear response in real time domain

A density matrix based time-dependent density functional theory is extended in the present work. Chebyshev expansion is introduced to propagate the linear response of the reduced single-electron density matrix upon the application of a time-domain δ -type external potential. The Chebyshev expansion method is more efficient and accurate than the previous fourth-order Runge-Kutta method and removes a numerical divergence problem. The discrete Fourier transformation and filter diagonalization of the first-order dipole moment are implemented to determine the excited state energies. It is found that the filter diagonalization leads to highly accurate values for the excited state energies. Finally, the density matrix based time-dependent density functional is generalized to calculate the energies of singlet-triplet excitations. © 2007 American Institute of Physics.published_or_final_versio

The Growth Of Highly Doped p-GaN On Sapphire By RF Plasma-Assisted Molecular Beam Epitaxy.

In this paper, we present the study of the electrical, structural and optical properties of p-type GaN grown on sapphire by RF plasma-assisted molecular beam epitaxy (RF-MBE)

Effects Of Thermal Annealing Of Pt Schottky Contacts On n-GaN.

In this paper, the Schottky behavior of Pt contact on n- GaN grown by RF-plasma assisted molecular beam epitaxy was investigated under different annealing temperatures

A comparative study of the electrical characteristics of metal-semiconductor-metal (MSM) photodiodes based on gan grown on silicon.

High quality Gan films are usually produced at high growth temperatures (> 1OOO°C) with the use of substrates such as sapphire (Ah03) or silicon carbide (SiC).Therefore, for a low production cost purpose, there has been a growing interest in producing lower growth temperatures Gan films as well as Gan based devices with low cost substrates such as silicon

Demonstration of microwave single-shot quantum key distribution

Security of modern classical data encryption often relies on computationally hard problems, which can be trivialized with the advent of quantum computers. A potential remedy for this is quantum communication which takes advantage of the laws of quantum physics to provide secure exchange of information. Here, quantum key distribution (QKD) represents a powerful tool, allowing for unconditionally secure quantum communication between remote parties. At the same time, microwave quantum communication is set to play an important role in future quantum networks because of its natural frequency compatibility with superconducting quantum processors and modern near-distance communication standards. To this end, we present an experimental realization of a continuous-variable QKD protocol based on propagating displaced squeezed microwave states. We use superconducting parametric devices for generation and single-shot quadrature detection of these states. We demonstrate unconditional security in our experimental microwave QKD setting. We show that security performance can be improved by adding finite trusted noise to the preparation side. Our results indicate feasibility of secure microwave quantum communication with the currently available technology in both open-air (up to $\sim$ 80 m) and cryogenic (over 1000 m) conditions.Comment: 9 pages, 3 figures, 1 supplementary information fil

Effects of Nitrogen Gas on the Growth of Magnesium Doped Indium Nitride Thin Films via Sol-gen Spin Coating Method

We report on the growth of magnesium doped indium nitride (InN Mg) thin films via sol-gel spin coating method followed by nitridation process. Special attention was paid to the effects of nitrogen (N2) gas on the nitridation process In this work , the nitridation processes were carried under ammonia with and without nitrogen ambiences. X-ray diffraction results reveal that lnN:Mg thin films deposited with nitrogen ambiences show formation of hexagonal structure InN layer with (1 01) preferential onentation. However, it was found that InN thin film grown under ambient with N2 gas has larger crystallite size (48.27 nm) as compared to that grown under the amb1ent without N2 gas (38.1 0 nm). Field emiss1on scanning electron microscopy results show that both deposited films exhibit coalesced island morphology with hexagonal like structure. Elemental composition analyses by X-rays dispersive spectroscopy reveal that sample grown under ambient with N2 gas has lower oxygen atomic percentage and higher ratio of indium to nitrogen as compared to that grown under ambient without N2 gas. Optical properties of the Mg doped InN thin films were investigated by means of Raman spectroscopy Two allowed Raman modes of wurtzite InN namely, E2(High) and A,(LO) modes, were clearl_y detected for both deposited films Nevertheless, the film grown under the present of N2 gas shows an additional feature corresponding to v4 vibration of the MgN4 tetrahedron at around 564cm1 . The presence of this feature indicates that the magnesium acceptors were activated and the compensation of Mg,n-N (LVM) was occured. Finally, all the results suggest that present of N2 gas during nitridation process will induce better grow of the wurtzite structure Mg-doped InN thin films

On the fraction of intermediate-mass close binaries that explode as type-Ia supernovae

Type-Ia supernovae (SNe-Ia) are thought to result from a thermonuclear runaway in white dwarfs (WDs) that approach the Chandrasekhar limit, either through accretion from a companion or a merger with another WD. I compile observational estimates of the fraction eta of intermediate-mass stars that eventually explode as SNe-Ia, supplement them with several new estimates, and compare them self-consistently. The estimates are based on five different methods, each utilising some observable related to the SN-Ia rate, combined with assumptions regarding the IMF: the ratio of SN-Ia to core-collapse rates in star-forming galaxies; the SN-Ia rate per unit star-formation rate; the SN-Ia rate per unit stellar mass; the iron to stellar mass ratio in galaxy clusters; and the abundance ratios in galaxy clusters. The five methods indicate that a fraction in the range eta~2-40% of all stars with initial masses of 3-8 M_sun (the generally assumed SN-Ia progenitors) explode as SNe-Ia. A fraction of eta~15% is consistent with all five methods for a range of plausible IMFs. Considering also the binarity fraction among such stars, the mass ratio distribution, the separation distribution, and duplicity (every binary can produce only one SN-Ia explosion), this implies that nearly every intermediate mass close binary ends up as a SN-Ia, or possibly more SNe-Ia than progenitor systems. Theoretically expected fractions are generally one to two orders of magnitude lower. The problem could be solved: if all the observational estimates are in error; or with a ``middle-heavy'' IMF; or by some mechanism that strongly enhances the efficiency of binary evolution toward SN-Ia explosion; or by a non-binary origin for SNe-Ia.Comment: MNRAS, accepted versio

Effect of Nitrogen Gas on the Growth of Magnesium Doped Indium Nitride Thin Films via Sol-gel Spin Coating Method

The growth of magnesium doped indium nitride (InN:Mg) thin films via sol-gel spin coating method followed by nitridation process was reported in this paper. In this work, the nitridation processes were carried under ammonia with and without nitrogen ambiences. X-ray diffraction patterns reveal that InN:Mg thin film grown under nitrogen ambiences show formation of InN (101) preferential orientation wurtzite structure. Field emission scanning electron microscopy results show that both deposited films exhibit coalesced island morphology with hexagonal like structure. Energy dispersive X-ray spectroscopy revealed that sample grown under ambient with N2 gas has lower oxygen atomic percentage and higher ratio of indium to nitrogen. Two allowed Raman modes of wurtzite InN, namely, E2(High) and A1(LO) modes, were clearly detected for the deposited films under N2 gas ambient. Nevertheless, the film grown under the present of N2 gas shows an additional feature corresponding to ν4 vibration of the MgN4 tetrahedron at around 564 cm-1. The presence of this feature indicates that the magnesium acceptors were activated and the compensation of MgIn-N (LVM) was occured. Finally, all the results suggest that present of N2 gas during nitridation process will induce better grow of InN:Mg thin films