P. Soundarrajan

Controlled (110) and (101) crystallographic plane growth of single crystalline rutile TiO2 nanorods by facile low cost chemical methods

A new approach has been employed to grow large size and high number density rutile TiO2 nanorods (NRs) by low cost chemical methods. Nuclei layers of low (~30 nm) and high (~150 nm) thickness have been optimized on glass substrates for growing NRs using spin coating and chemical spray pyrolysis methods respectively. The scanning electron and atomic force microscopic images clearly show that randomly aligned, large size, exotic NRs have grown on low thickness seed layers at a high temperature (180 °C), and that interconnected, NRs with good number density have grown on high thickness seed layers at a low temperature (120 °C) via hydrothermal synthesis. The structural studies clearly reveal that the as-grown NRs have tetragonal rutile structures with different anisotropic crystallographic plane growth along the c-axis. The preferentially oriented (110) Bragg reflection in the large size NRs and (101) Bragg reflection in the number dense NRs illustrate that the Ti atoms are positioned in the middle of the atomic layer and stimulate randomly standing NRs along the direction of stacking. The growth orientation and single crystalline nature of the NRs are confirmed by high resolution transmission electron microscopy and μ-Raman scattering. The absorbance value and the shift in the UV-vis energy region of the TiO2 NRs are strongly dependent on the number density and/or size of the NRs. The crystal defects of the prepared rutile TiO2 NRs are analyzed using photoluminescence spectra. Our results show that the thickness of the seed layer and the growth temperature play a pivotal role in determining the two anisotropic crystallographic plane growths of rutile TiO2 NRs.

Hydrophilic CdSe thin films by low cost spray pyrolysis technique and annealing effects

Cadmium selenide (CdSe) thin films were deposited on glass substrates at 200°C by homemade chemical spray pyrolysis technique. The as-deposited films were annealed in air atmosphere for 3 hrs, at two different temperatures (350 and 450°C). The as-deposited film has been observed to possess uniform surface with crystalline sphalerite cubic structure and optical band gap of Eg = 2.4 eV. It is worth noting that after annealing, metastable cubic sphalerite phase transforms into stable well crystalline hexagonal wurtzite phase. The optical band gap was found to decrease from 2.4 eV to 1.75 eV. The average surface roughness is 1.5 nm for the as-deposited film which rises to 4.2 nm after annealing the film in air atmosphere. The contact angle was found to vary from 94° ± 1° to 81° ± 1° with annealing temperature. In addition, from Wenzel’s relation it is concluded that CdSe thin film is hydrophilic in nature.

Enhancing resistive-type hydrogen gas sensing properties of cadmium oxide thin films by copper doping

The pure and Cu-doped CdO thin films with various doping concentrations (0.5 to 2 wt%) were deposited on amorphous glass substrates by a chemical spray pyrolysis technique for hydrogen gas sensor application. The crystallinity, morphology, optical and electrical properties of the CdO thin films were effectively modified by Cu doping. The CdO film exhibited a cubic crystal structure, which is retained after Cu doping with significant changes in the preferential orientation of the crystallographic plane. The SEM and AFM images clearly revealed that the grain size and roughness of the CdO film changed with the Cu doping level. The expected element compositions were initially identified by EDAX and then authentically confirmed by XPS to determine its binding energy states. The optical transmittance and near band edge emission (NBE) bands of the CdO film were significantly decreased by Cu doping level. The minimum resistivity (2.01 × 10−3 Ω cm) as well as good mobility (19.5 cm2 V−1 s−1) and maximum carrier concentration (1.98 × 1020 cm−3) were obtained for the 1 and 0.5 wt% Cu-doped CdO thin films. The Cu-doped CdO thin films exhibit better hydrogen gas sensing behaviour than that of pure CdO film. Finally, it is concluded that the maximum sensitivity is vividly achieved for the Cu-doped CdO thin film at 1 wt%.