Abstract: A variety of electrochemical and electrical techniques is employed in order to determine useful parameters of the optical behaviour of thin semiconducting films. In particular, this work is intended to the characterization of cathodically electrodeposited binary and ternary cadmium and zinc selenides and tellurides by photoelectrochemical (PEC) tests. Typical solid-state techniques,
such as reflection, laser assisted photoreflection, resistivity and Hall effect measurements are used as well. A plain relation between crystal structure/film morphology and PEC behavior is established so long as the electrochemical preparation method is capable to explicitly control the deposit structure. In certain cases, a particular charge transfer mechanism in the semiconductor, associated
with the existence of a nanostructure, is shown to result in higher photoconversion efficiencies as compared to larger-grained films.
Abstract: This paper reports on the gamma radiation-induced changes in thin oxide films deposited by thermal vacuum technique. Structures of various oxides thin films, such as In2O3, SiO and TeO2 and their mixtures in different proportions were studied. The influence of gamma radiation on In2O3/SiO films has resulted in significant changes in the microstructure of this film. Some kind of agglomerations with variable sizes in the range 0.5-3 µm has occurred. After a dose of 8160 µSv an
evidence of partial crystallisation was observed with X-ray diffraction. Structural changes in TeO2 thin film were explored by means of Raman spectroscopy. After they have been exposed to g- radiation, a strong peak appeared at 448.83 cm-1, indicating further transformation to g-TeO2 modification.
Abstract: The formation of a carbonate-containing hydroxyapatite, HCAp, layer on bioactive
calcium silicate sol-gel glass of the formula (CaO)0.3(SiO2)0.7 has been studied in-vitro in Simulated Body Fluid (SBF). Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES), X-ray diffraction (XRD), and solid state nuclear magnetic resonance (NMR) measurements have been performed with results showing the formation of a significantly amorphous HCAp layer after less than 5 hours in solution.
Abstract: Monitoring of elemental composition of structural concrete is required to protect
reinforcing steel in concrete against corrosion. Prompt Gamma Neutron Activation Analysis (PGNAA) technique has been used to measure the elemental composition of concrete samples. In this study 2.8 MeV neutron-based PGNAA setup at King Fahd University of Petroleum and Minerals (KFUPM) has been tested for elemental analysis of concrete sample. Later the setup will be used to
measure chloride and sulfate ion concentration in concrete samples. Corrosion of reinforcing steel in concrete is believed to be caused by chloride and sulfate ions.
In the KFUPM PGNAA facility the prompt gamma rays are produced through capture of thermal neutrons in bulk sample. The sample size, to be used with PGNAA setup, is determined through Monte Carlo simulations. In this study, prompt gamma ray yield from calcium and silicon present in the concrete sample was measured for various thickness of the front moderator of the PGNAA setup.
The experimental yield of prompt gamma ray was compared with the results of the Monte Carlo simulations and an excellent agreement has been achieved between the two. The study has shown that the PGNAA technique can be successfully applied for elemental analysis of the concrete samples
Abstract: The complete optical gyration tensor of monoclinic pure L-arginine phosphate
monohydrate (LAP) and deuterated LAP (d-LAP) crystals has been determined. Variation of the optical activity in the presence of birefringence of d-LAP crystal with pure LAP is found from the high-accuracy universal polarimeter (HAUP) method at a wavelength of 632.8 nm. The gyration tensor components in terms of rotatory power were found to be r11 = -6.6(3) º/mm, r22 = 19(2)
º/mm; r33 = 49.7(7) º/mm; and r13 = -43.7(8) º/mm for the LAP, and r11 = -1.2(1) º/mm, r22 = 5.0(4) º/mm; r33 = 41.4(3) º/mm; and r13 = -38.0(4) º/mm for d-LAP at room temperature.
Abstract: Currently, many semiconductor compounds, particularly Cd1-xZnxTe, have attracted attention for applications in detection of radiation, due to the very good resolution without cryogenic cooling (a 1.3 keV-FWHM at the 122 keV line from 57Co is reported for some detectors). In this study the properties of a zinc doped cadmium telluride detector mounted on a thermoelectric cooler (Amptek Inc., model XR-100T-CZT) were studied. The detection system is based on a Cd0.9Zn0.1Te crystal of 3x3x2 mm, which operates at approximately -21°C and uses a rise time
discrimination (RTD) circuit to improve the energy resolution. Although the quantum efficiency of this compound is very high, the small dimensions of the crystal limit its use to low energy photons (some hundreds of keV). Because of the carrier trapping characteristics of CZT, the experimental determination of the response function is essential. In this work it was measured in the range of
energies from 10 to 400 keV, employing gamma rays and fluorescence x-rays from different sources (57Co, 133Ba, 152Eu and 241Am). In spite of the experimental difficulties, the x-ray escape fraction was also evaluated, making it possible the correction of the distortion it causes in the measured spectra. Measurements of x-ray spectra produced by a tungsten tube operating at small currents were carried out, and the stripping procedure was performed, taking into account the two
contributions (efficiency and escape fraction). Results obtained point to the feasibility of use of this detector for in-situ diagnostic x-ray spectroscopy, provided that low intensity beams are available.
Abstract: Long-wavelength vertical cavity surface emitting lasers (VCSELs) operating in the 1.3 µm to 1.5 µm wavelength range are considered the best candidate for the future low-cost reliable light sources in fiber communications. However, the room temperature performance of GaInAsP/InP long-wavelength InP lattice matched material system falls below the shortwavelength VCSELs. In this work we present the results of our studies concerning I-V and electroluminescence measurements on GaInAsP/InP structure with distributed Bragg reflectors. The device lased at 0.98 µm at room temperature.
Abstract: Silicon carbon nitride (SiCN) films have been deposited on silicon wafers by microwave plasma chemical vapor deposition (MPCVD). Gas mixture of H2, CH4, N2, and SiH4 was used as precursors, in which the flow rate of N2 was changed. X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy were employed to characterize the composition and bonding structures, while field-emission scanning electron microscopy were used to investigate the microstructure of the films. With increasing the flow rate of N2 from 50 sccm to 300 sccm, the SiCN films changed from amorphous to nanocrystalline. Characteristic current-voltage measurements indicate a low turn-on field of 10.8 V/µm. Field emission current density of 4.5 mA/cm2 has been observed at 20
Abstract: Carbon nitride films were grown on Si substrates by a microwave plasma chemical vapor deposition method, using mixture of N2, CH4 and H2 as precursor. Scanning electron microscopy shows that the films consisted of a large number of hexagonal crystallites. The dimension of the largest crystallite is about 3 µm. The X-ray photoelectron spectroscopy suggests that nitrogen and carbon in the films are bonded through hybridized sp2 and sp3 configurations. The X-ray diffraction
pattern indicates that the major part of the films is composed of α-, β-, pseudocubic C3N4 and graphitic C3N4. The Raman peaks match well with the calculated Raman frequencies of α- and β-C3N4, revealing the formation of the α- and β-C3N4 phase.