Akash Singh

Synthesis and single crystal growth of gallium phosphide by the liquid encapsulated vertical Bridgman technique

Gallium phosphide is a typical III–V compound semiconductor and is also an important electronic material. The synthesis and single crystal growth of this compound by melt methods is rendered very difficult because of the large phosphorus vapour pressure. A high pressure vessel with internal heating and a quartz reactor was first developed for the direct synthesis of gallium phosphide. The crystal growth was carried out in a second high pressure chamber rated for 100 bars gas pressure and equipped with the paraphernalia for crystal growth. Single crystals of gallium phosphide were grown from the polycrystalline starting material by the vertical Bridgman method and the vapour pressure problem was overcome by encapsulating the melt in a column of molten boric oxide. Both boron nitride and silica were employed as crucibles, and with the former, single crystal rods of 8–10 mm diameter and 10–15 mm length were obtained.

Residual stress measurements in electron beam evaporated yttria doped zirconia films deposited on Si (111) substrates

Zirconia thin films with varying yttria concentrations (0, 4, and 10 mol. %) were grown on Si (111) substrates using electron beam physical vapor deposition technique. The residual stress as a function of depth on undoped and yttria doped zirconia films with different phases was determined using the modified sin2ψ technique by varying the x-ray angle of incidence. Surface profilometry was also used as a complementary technique for qualitative measurement of stress in these films. The residual stress profile revealed that tensile residual stress was present in the near-surface region and it decreased rapidly as a function of depth in all three films with different yttria concentration. The possible reasons for the film growth stress and stress gradient in the yttria doped zirconia films with different concentration of yttria are discussed.

Structural and optical properties of electron beam evaporated yttria stabilized zirconia thin films

Yttria stabilized zirconia (10 mole % Y2O3) thin films were deposited on quartz substrates using electron beam physical vapor deposition at the substrate temperatures in the range 300 – 973 K. XRD analysis showed cubic crystalline phase of YSZ films with preferred orientation along (111). The surface roughness was found to increase with the increase of deposition temperatures. The optical band gap of ∼5.7 eV was calculated from transmittance curves. The variation in the optical properties is correlated with the changes in the microstructural features of the films prepared as a function of substrate temperature.

Microstructural, nanomechanical and tribological properties of ZrAlN thin films prepared by pulsed DC magnetron sputtering

An investigation on the structural, nano-mechanical and tribological properties of thin films of ZrAlN deposited on (100) Si and D-9 alloy substrates prepared by pulsed DC magnetron is reported. Zr1-xAlxNy films have been studied with the Al concentration range of 0<;x<;0.36 Al. It was observed that values of hardness and Youngs modulus of the alloyed ZrAlN films were in the range 9-18 GPa and 235-365 GPa, respectively. Tribological studies of ZrAlN thin film showed that the coefficient of friction of alloyed films of ZrAlN was lower for the steel ball (100Cr6 steel) than that for the Al2O3 ball up to 36 at.% of Al.