The crystal structural and optical properties of the ordered defect compound CuGa5Se8 grown by the vertical Bridgman–Stockbarger method have been studied by x-ray diffraction and optical absorption techniques, respectively. The analysis of the x-ray diffraction data shows that the material crystallizes in a tetragonal chalcopyrite-related structure with unit cell parameters a=5.4732(8) and c=10.931(6) Å. Optical data shows that the band gap energy EG varies from 1.917 to 1.811 eV in the temperature range between 10 and 300 K. It is found that the variation of EG with T is mainly due to the contribution of optical phonons with a characteristic phonon energy of about 19 meV. The optical absorption coefficient just below the absorption edge varies exponentially with photon energy confirming the existence of the expected Urbach’s tail. The phonon energy hνp associated with Urbach’s tail, which is found to be 54 meV, is about two times higher than the highest optical phonon mode reported for ternary semiconductors of the Cu–Ga–Se system. The origin of higher energy is attributed to the contribution of localized modes produced by structural disorders of low energy formation mainly due to deviation from ideal stoichiometry.
Dispersion relations and polarizations for surface waves in infinite planar
samples in the QHE regime are explicitly determined in the small wavevector
limit in which the dielectric tensor can be considered as local. The wavelength
and frequency regions of applicability of the results extends to the infrared
region for typical experimental conditions. Then, standard samples with
millimetric sizes seem to be able to support such excitations. Forced
oscillations are also determined which should be generated in the 2DEG by
external electromagnetic sources. They show an almost frequency independent
wavevelength which decreases with the magnetic field. A qualitative model based
in these solutions is also presented to describe a recently found new class of
resonances appearing near the edge of a 2DEG in the QHE regime.Comment: latex file, 18 pages, 3 figures, spelling correcte
Nickel based self-fluxing thermal sprayed alloys have been used in many applications to protect machinery parts against wear and corrosion. Although the mechanical and chemical properties of nickel based self-fluxing coatings are well known, the constituents of the microstructure have not been fully analysed. In the present work, the coatings were thermal sprayed on a 1020 steel substrate using a JP-5000 gun. Scanning electron microscopy and transmission electron microscopy techniques were employed for microstructural characterisation of the coatings, as complementary techniques to the X-ray diffraction studies already published by the authors. It has been determined that the as sprayed coatings are formed by a multiphase structure with an inhomogeneous distribution of soluble elements in an FCC c Ni matrix. However, a well distributed network of hard phases in the matrix has been found and these were identified as: silicides (Ni 2 Si), borides (W 2 B, B 4 Si, CrB 41 ,W 5 (Si,B) 3 , Cr 3 B 5 ) and carbides (M 23 C 6 type carbides where metals are Cr, W, Si and Ni). Also, some other complex phases such as C 0 . 17 Fe 0 . 81 Si 0 . 02 and Ni 2 . 9 Cr 0 . 7 Fe 0 . 36 were found. In particular, the existence of the borides had not been reported in the literature before possibly owing to their small size, of y0 . 31 mm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.