A. Asadov

Magnetic and optical properties of the InCrN system

Room-temperature ferromagnetic In1−xCrxN films with x ranging from 0.0005 to 0.04 and antiferromagnetic CrN films have been grown by plasma-assisted molecular-beam epitaxy. Electron and x-ray-diffraction techniques could find no evidence for precipitates or phase segregation within the films. Ferromagnetism was observed in the In1−xCrxN layers over a wide range of Cr concentrations, with the magnitude of the ferromagnetism found to correlate with the background carrier concentration. Higher n-type carrier concentrations were found to lead enhanced ferromagnetism, with maximum saturation and remnant moments of 7 and 0.7emu∕cm3, respectively. The addition of Cr to the InN matrix led to reduced photoluminescence intensity and a shift of the peak to higher energy. These observations along with a band-gap-like optical transmission feature at 0.7 eV suggest that CrN has an indirect gap of approximately 0.7 eV and a direct Γ-valley gap greater than 1.2 eV.

CHARACTERIZATION OF BST PRODUCED BY HIGH TEMPERATURE HYDROTHERMAL SYNTHESIS

Barium strontium titanate (BST) was produced in a teflon lined pressure vessel using a high temperature hydrothermal technique and controlling the processing parameters of Ba+Sr concentration, Ba and Sr ratio, temperature, reaction period and TiO2 concentration. It was found that this technique produces BST powders of less than 200 nm particle size with high degree of crystallinity. However, most BST powders tend to be strontium rich. Thus, excess barium in the initial solution was essential in order to produce a high barium content in the final product, which was important to obtain good electrical properties. A high TiO2 concentration was also crucial in producing BST with a high Ba content, though this parameter was responsible for a multiphase structure. The period of hydrothermal reaction was important for stoichiometric reaction.

Crystal structure development of vanadium oxide thin films deposited by a magnetron sputtering technique

Crystal structure of vanadium oxide films with different thickness, deposited on glass and F:SnO2 coated (FTO) substrates, was studied. It was found that all the films annealed at 450 °C developed a metastable β-V2O5 monoclinic crystal structure, represented by crystals of up to 100 nm. At higher temperatures, the original crystals of relatively thick films of 400 nm on the glass substrate first increased in size and improved their crystal structure symmetry from the monoclinic to tetragonal, then gradually intergrew into spectacular superstructures of crystal “leaves” (500 °C) and “needles” (550 °C). Thin films of 130 nm exhibited a similar crystallization processes but at a higher rate. It was found that the FTO substrate supported the slowest crystal growth dynamics with annealing temperature. The original crystals did not grow in size and retained their low β monoclinic symmetry in the whole temperature range up to 550 °C. The superstructure appeared around film imperfections in the form of plate macr...