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[en] The temperature dependent photon masses at high temperature are computed. It is shown that, for a real photon, only the transverse components develop temperature dependent masses. Although diverging terms appear in the photon self energy in the case of a real photon at high temperature, they are shown not to contribute to the effective masses. A general formula for the temperature dependent photon masses is obtained. (Author)
[en] A square root of a momentum space is introduced. In this process an 8-dimensional complex manifold and an internal symmetry group U(2,2) are obtained. The complex Clifford algebra of U(2,2) natually leads to a kind of square root of the Dirac-Weyl operator. A possible application to neutrinos is discussed. (Author)
[en] The Regge trajectory of a dyon potential is studied with results that there exist resonances for angular momentum greater than lh, with a half width of linear energy dependence. A branch cut is shown to occur in the complex angular momentum plane of the scattering amplitude. (author)
[en] Polarization-field effects on the vertical transport in GaN/AlGaN resonant tunneling diodes (RTDs) were theoretically investigated by using the transfer matrix formalism. The self-consistent model shows that the resonant peaks are shifted toward higher energies with increasing Al composition in the AlGaN barrier, and the transmission probability values are shown to decrease rapidly. In the case of the flat-band model, on the other hand, the shift of the resonant peaks is smaller than it is for the self-consistent model and the variation of transmission probability values with increasing Al composition is relatively smaller than that of the self-consistent model. The current voltage characteristics of the self-consistent model are asymmetric while those of the flat-band model are symmetric for positive and negative current directions. The peak-to-valley ratio (PVR) of the self-consistent model is shown to be slightly smaller than that of the flat-band model for Al = 0.3.
[en] Cu-In-Se thin precursors were prepared by using the DC co-sputtering method and were then irradiated using an in-situ electron beam (e-beam) irradiation unit, which was equipped with a cosputtering chamber. The irradiation time of the samples was varied from 0 sec to 300 sec, and the electron dose and intensity were kept constant with 200 W of RF power and 2.5 kV of DC power. As the irradiation time was increased to 300 sec, the grain size gradually increased with a few voids, and the XRD patterns showed several polycrystalline peaks of CuInSe2 (CIS). Also, the Raman crystalline peak at 173 cm-1 indicated excellent crystallinity of the CIS single phase, with a greater improvement and sharpness shown at higher irradiation times. The compositional ratio of Cu:In:Se after e-beam irradiation remained almost the same as that of the DC co-sputtered precursors. As the irradiation time was increased to 300 sec, the Hall mobility, resistivity, and carrier concentration were 0.14 cm2/Vs, 2.16 x 10-4 Ω cm, and 7 x 1022 cm-3, respectively. E-beam irradiation without the addition of selenium might be a good candidate as a rapid crystallization and annealing method for making Cu-In-Se precursors for the preparation of CIS absorber materials.
[en] By means of time-resolved magneto-optical measurements under very low-power ultrafast laser excitation (∼2 μJ/cm2) a strong magnetic linear dichroism (MLD) effect is observed in a 10 nm-thick Fe film grown on an n-doped GaAs (001) by using molecular beam epitaxy (MBE). The dynamic magneto-optical responses are found to depend strongly on the orientation of the polarization of the probe beam, indicating that a strong MLD response is present in the Fe/GaAs hybrid structure. Our observations provide an efficient way to enhance the detective sensitivity when dealing with the weak magneto-optical response under very low-power optical pumping by choosing an appropriate orientation of the probe's polarization. This method can also be applied to other ferromagnetic thin films to measure the full three-dimensional magnetization vector without changing the sample's orientation or the optical detection geometry.
[en] AlN seed layers with a thickness of 50 nm were grown by using nitrogen plasma-assisted molecular beam epitaxy on (110) Si substrates with different V/III ratios in the temperature range from 850 .deg. C to 940 .deg. C. In varying the Al/N ratio and the growth temperature, distinct surface morphologies emerge, which are quite different from those observed in AlN growth on (111) Si substrates. Under N-rich conditions, AlN films exhibits randomly distributed islands with different sizes ranging from 10 nm to 1 m. In Al-rich conditions, two distinct surface morphologies, (1) closely-packed islands preferentially aligned along the AIN /Si azimuth and (2) smooth flat surfaces, are observed at various growth temperatures. The observed morphology transition is attributed to the asymmetric strain distribution between hexagonal symmetric AlN layers and rectangular (110) Si substrates and to varying surface adatom migration rates present at different growth temperatures.
[en] We have studied the important astrophysical 3He(α,γ)7Be and 3H(α,γ)7Li reactions in the framework of a potential model. 3He(α,γ)7Be and 3H(α,γ)7Li processes are key reactions in both big bang nucleosynthesis and the p-p chain of hydrogen-burning in stars. The stellar 3He(α,γ)7Be and 3H(α,γ)7Li reactions were analyzed at low energies on the basis of a direct radiative capture mechanism. The astrophysical S-factors near zero energy were calculated without using the effective expansion of the S-factor or the asymptotic wave functions. In this paper, 3He(α,γ)7Be and 3H(α,γ)7Li radiative capture reactions at very low energies are taken as a case study. Using the M3Y potential, we have calculated the astrophysical S-factors for the E1 transition. In comparison with other theoretical methods and available experimental data, excellent agreement is achieved for the astrophysical S-factors of these processes.
[en] In this work, the RF-dressed potentials generated using a static magnetic field of a quadrupole trap and various radio frequency (RF) fields have been theoretically investigated for trapping and manipulating of cold atoms in a two-dimensional (2D) geometry. In this scheme, the RF fields of some particular polarizations and phases are shown to give rise to some novel static and timedependent anisotropic two-dimensional potentials that are useful to trap and manipulate the cold atoms in the 2D geometry. The generated time-dependent 2D potentials, rotating on a circular ring, can be used to control the rotation and the oscillation of the cold-atom cloud on the path of the circular ring. The ultracold atoms trapped in these potentials may be used to investigate interesting physics phenomena, such as tunnelling and superfluidity.
[en] We have studied a silicon semiconductor detector as an alternative to commercial 3He-gas-based neutron detectors. In this paper, we present a measurement of the energy spectrum of neutron-induced secondary radiation by using a silicon detector. Polyethylene was used to produce thermal neutrons by using a 252Cf radioactive source. The photodiode was then irradiated by thermal neutrons, followed by a 10B converter that produced charged particles. This configuration was found to have a better response to neutrons than a moderator-converter-photodiode configuration. By comparing the measurements with Geant4 simulations, the air gap between the photodiode and the converter was determined to be 0.3 mm and the detector response of the semiconductor device was found to be a smeared Gaussian function with σ = 0.1.