Lower Intensity Ratio Research Articles

Improvement of crystallinity of CdZnTe epilayers on GaSb substrates by ZnTe buffer layer

Thick CdZnTe epitaxial film is a promising alternative for X-ray detectors, especially in the case of large-area imaging application. One of the key issues in growing thick heteroepitaxial film with high crystallinity is to reduce the mismatch dislocations that appear at the interface between CdZnTe epilayer and the substrate. In this paper, we prepared CdZnTe films without and with ZnTe buffer layers on GaSb (001) substrates by the closed space sublimation. All preparation conditions for ZnTe buffer layers, CdZnTe epilayers on ZnTe buffers and GaSb substrates, as well as the pretreatment of GaSb surface have been optimized through tremendous experiments. The results of electron backscatter diffraction and transmission electron microscope observation prove that ZnTe buffer layers suppress (1‾1‾1)M twins extending from GaSb. The deposition temperature for inserting ZnTe buffer about 495 K is optimized for getting smooth ZnTe surface, on which high crystalline quality CdZnTe epilayer with a narrower full-width at half-maximum (85 arcsec) of double crystal X-ray rocking curve for (004) reflection and lower intensity ratio IDcomplex/I(D0, h) of low-temperature photoluminescence spectroscopy were produced.

Plasma preparation method and tribological properties of diamond-like carbon coating on magnesium alloy AZ31 substrate

Magnesium alloys are light weight and exhibit good recyclability but suffer from low hardness and wear resistance. In this study, the hardness and wear resistance of AZ31 magnesium alloy were improved by depositing diamond-like carbon (DLC) films as hard protective coatings using ion-beam-enhanced deposition with various CH4/H2 ratio, gas flow rates and accelerating voltages. The supporting effect of the magnesium alloy was enhanced by the production of a graded interfacial layer which is composed of film atoms and substrate atoms. The composition and mechanical properties of the DLC coatings were characterized using scanning electron microscopy (SEM), Raman spectroscopy, Rockwell test and nano-indentor. The tribological properties of the coating were also investigated using a frictional surface microscope with an in situ observation system and friction force measurements. The DLC films were characterized by a lower intensity ratio of the D-peak to G-peak (ID/IG), higher hardness, and improved tribological properties when deposited at a lower accelerating voltage (6 kV). At the CH4/H2 ratio of 1:99 and 6 sccm/6 kV, minimum ID/IG values of 0.62, relatively low friction force value of 0.12 N, and a maximum hardness of 4056HV were attained respectively. In addition, the DLC film exhibited improved wear resistance and a shallower wear track at this condition.

Oscillation of nonvolatile holographic recording in LiNbO3:Fe:Cu crystals

The oscillation of diffraction efficiency is observed in the nonvolatile holographic recording of lithium niobate crystals doped with iron and copper. The physics of oscillation in doubly doped lithium niobate crystals is studied by using Runge–Kutta methods, and the oscillation can be attributed to the redistribution of electrons in the deeper and shallower traps of the crystals in the initial phase of holographic recording. The effects of Fe concentration and intensity ratio of red beams to UV beam (IR/IUV) on the oscillation are investigated theoretically. The results show that with lower Fe concentration, the amplitude of oscillation is larger and with lower intensity ratio IR/IUV, the duration of the oscillation is longer.

Chemical bonding in Tl cuprates studied by x-ray photoemission

Epitaxial thin films of the Tl cuprate superconductors ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8},$ ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{10},$ and ${\mathrm{Tl}}_{0.78}{\mathrm{Bi}}_{0.22}{\mathrm{Ba}}_{0.4}{\mathrm{Sr}}_{1.6}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{9\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ are studied with x-ray photoemission spectroscopy. These data, together with previous measurements in this lab of ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\mathrm{\ensuremath{\delta}}}$ and ${\mathrm{TlBa}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}},$ comprise a comprehensive data set for a comparative study of Tl cuprates with a range of chemical and electronic properties. In the Cu $2p$ spectra, a larger energy separation between the satellite and main peaks ${(E}_{s}\ensuremath{-}{E}_{m})$ and a lower intensity ratio ${(I}_{s}{/I}_{m})$ are found to correlate with higher values of ${T}_{c}.$ Analysis of these spectra within a simple configuration interaction model suggests that higher values of ${T}_{c}$ are related to low values of the $\mathrm{O}2\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{Cu}3d$ charge transfer energy. In the $\mathrm{O}1s$ region, a smaller bond length between Ba and Cu-O planar oxygen is found to correlate with a lower binding energy for the signal associated with Cu-O bonding, most likely resulting from the increased polarization screening by ${\mathrm{Ba}}^{2+}$ ions. For samples near optimum doping, maximum ${T}_{c}$ is observed to occur when the Tl ${4f}_{7/2}$ binding energy is near 117.9 eV, which is near the middle of the range of values observed for Tl cuprates. Higher $\mathrm{Tl}{4f}_{7/2}$ binding energies, corresponding to formal oxidation states nearer ${\mathrm{Tl}}^{1+},$ are also found to correlate with longer bond lengths between Ba and Tl-O planar oxygen, and with higher binding energies of the $\mathrm{O}1s$ signal associated with Tl-O bonding.