K. M. K. Srivatsa

Synthesis of Anatase Titania Nanostructures at room temperature by PECVD technique

Anatase titania nanostructures have been synthesized at room temperature by plasma enhanced chemical vapor deposition (PECVD) process on silicon (100) substrates using titanium tetraisopropoxide [Ti(OC3H7)4, TTIP] vapor, argon and oxygen mixtures under various deposition pressures. The deposited titania has been characterized for its structural, morphological and chemical composition by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray (EDX) spectroscopy and Fourier transform infrared (FTIR) spectroscopy recordings. With the variation of deposition pressure, titania assumes various nanostructures viz. nanocrystals, nanoparticles, noanorods and comb-like structure. EDX and FTIR measurements show that the deposited titania is of high chemical purity. The possible growth mechanisms for the observed titania nanostructures have been discussed.

Effect of Oxygen Admittance Temperature on the Growth of ZnO Microcrystals by Thermal Evaporation Technique

Hexagonally well-faceted microcrystals of ZnO have been grown by thermal evaporation of Zn powder in oxygen ambient at 700 °C under atmospheric pressure. It has been observed that the properties (size and quality) of ZnO microcrystals have a strong dependence on the reactor temperature at which the oxygen gas is admitted into the growth zone. The microcrystals grown with oxygen admittance at 450 °C have a length of 1 μm and a diameter of 0.75 μm while that grown with oxygen admittance at 600 °C have a length of 1.5–2 μm and a diameter of 1 μm. Room temperature photoluminescence spectra show a ultraviolet (UV) emission peak at 385 nm with a green band emission at around 500 nm. The UV-to-green band emission ratio for the microcrystals grown with oxygen admittance at 450 °C is observed to be 1.25 and the ratio decreases to 0.45 for the sample grown with oxygen admittance at 600 °C.