K. Sethuraman

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.

Third-Harmonic Generation of Regioregular Poly(3-hexylthiophene) Thin Films Prepared Using Two Solution Methods

In this paper, we report on the third-order nonlinear optical properties of poly(3-hexylthiophene) (P3HT) thin films prepared using solution methods. The third-order optical susceptibilities χ(3)(-3ω;ω,ω,ω) of P3HT thin films spin-coated and drop-cast on quartz glass substrates were estimated from optical third harmonics measured using the Maker-fringe method. The orientation, alignment, and crystallinity of the P3HT thin films obtained were evaluated using atomic force microscopy (AFM), X-ray diffraction (XRD) analysis, and UV–visible absorption spectra. The maximum nonlinear optical susceptibility χ(3) (NLOS), as estimated from the drop-cast film, was 1.55×10-8 esu, which was higher than that of a spin-coated film by one order. The enhancement of χ(3) is associated with the orientation and crystallinity of the P3HT molecule on the substrate.

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%.

Hierarchical architecture of CuInS2 microsphere thin films: altering laterally aligned crystallographic plane growth by Cd and V doping

The hierarchical architecture of pristine and cadmium (Cd) and vanadium (V) doped copper indium disulphide (CuInS2 (CIS)) microsphere thin films grown on spray coated seed layers by a wet chemical method is demonstrated. First, nano-flakes of self-assembled porous (NFSAP)-CIS microspheres have been optimized on a CIS seed layer by controlling the synthesis strategy. Later, Cd and V were incorporated as foreign impurity ions into the NFSAP-CIS microspheres. The pristine and doped CIS microsphere films resulted in a body-centered-tetragonal crystal structure which was confirmed from the XRD and SAED patterns. The electron microscope images clearly depict the formation of a solid and an elongated NFSAP-CIS microsphere under Cd and V doping, respectively. The change in morphological structure was attributed to the suppression and expansion of the laterally oriented crystallographic plane. The chemical composition and optical and electrical properties of the pristine and Cd and V doped CIS films were determined by UV-vis, photoluminescence, XPS, and Hall measurements. The Cd and V doped CIS microsphere films have superior photoelectric response compared to the pristine CIS films. The controlled laterally oriented crystallographic plane in CIS microspheres brought about by doping induces the modification in the surface morphological structure that results in improved electrical and photo-physical properties. The results of this study provide a framework for fabricating an optimized CIS absorber layer in photovoltaic devices.

Investigation on vanadium oxide thin films deposited by spray pyrolysis technique

Vanadium oxide thin films were deposited at 400 °C by spray pyrolysis technique using 0.1 M aqueous precursor solution of ammonium meta vanadate (AMV) with two different pH values. X-ray diffraction results showed that the film prepared using aqueous precursor AMV solution (solution A; pH 7) is amorphous in nature and the film prepared by adding HNO3 in the AMV aqua solution A (solution B; pH 3) is polycrystalline in nature. Vanadium oxide film prepared from the precursor solution B is in the mixed phases of V2O5 and V4O7. Crystallinity is improved for the film prepared using solution B when compared to film prepared from solution A. Crystallite size, strain and dislocation density calculated for the film prepared from solution B is respectively 72.1 nm, 0.4554 × 10−3 lin.−2m−4 and 1.7263 × 1014 lin.m−2. Morphology study revealed that the size of the flakes formed on the surface of the films is influenced by the pH of the precursor solution. Average Visible Transmittance and maximum transmittance of the d...

Low power optical limiting studies on nanocrystalline benzimidazole thin films prepared by modified liquid phase growth technique

In the present work, benzimidazole (BMZ), a well known nonlinear optical material, thin films were deposited using the modified liquid phase growth technique at different solution temperatures. The prepared samples were subjected to spectral, structural and surface analyses. Linear optical properties and third-order optical nonlinearity of the deposited BMZ thin films were analysed using UV–visible–NIR spectrum and Z-scan technique, respectively. The experimental results show that the BMZ films exhibit reverse saturable absorption and positive nonlinearity at 650 nm CW laser of power 5 mW. The measured third-order nonlinear susceptibility of the films is about 10−10 esu. Optical limiting studies were performed using the same laser source and the potentiality of the BMZ films is reported.