K. Sreenivas

Analysis of ultraviolet photoconductivity in ZnO films prepared by unbalanced magnetron sputtering

Photoresponse characteristics of polycrystalline ZnO films prepared by the unbalanced magnetron sputtering technique have been analyzed for ultraviolet photodetector applications. Changes in the cr ...

Response speed of SnO2-based H2S gas sensors with CuO nanoparticles

CuO nanoparticles on sputtered SnO2 thin-film surface exhibit a fast response speed (14 s) and recovery time (61 s) for trace level (20 ppm) H2S gas detection. The sensitivity of the sensor (S∼2.06×103) is noted to be high at a low operating temperature of 130 °C. CuO nanoparticles on SnO2 allow effective removal of excess adsorbed oxygen from the uncovered SnO2 surface due to spillover of hydrogen dissociated from the H2S–CuO interaction.

Cholesterol biosensor based on rf sputtered zinc oxide nanoporous thin film

Cholesterol oxidase (ChOx) has been immobilized onto zinc oxide (ZnO) nanoporous thin films grown on gold surface. A preferred c-axis oriented ZnO thin film with porous surface morphology has been fabricated by rf sputtering under high pressure. Optical studies and cyclic voltammetric measurements show that the ChOx∕ZnO∕Au bioelectrode is sensitive to the detection of cholesterol in 25–400mg∕dl range. A relatively low value of enzyme’s kinetic parameter (Michaelis-Menten constant) ∼2.1mM indicates enhanced enzyme affinity of ChOx to cholesterol. The observed results show promising application of nanoporous ZnO thin film for biosensing application without any functionalization.

Preparation and characterization of rf sputtered indium tin oxide films

Indium tin oxide films have been grown by rf sputtering at various Ar‐O2 mixtures, at low substrate temperatures (200 °C), and deposition rates (25 A/min), followed by post deposition annealing (at 350 °C) in different ambients (O2, N2, and cracked ammonia). Influence of a reactive gas (oxygen) on the sputtering rate of a metallic (indium/tin) alloy target has been investigated. Growth parameters and annealing conditions have been optimized. The films were characterized by electron and x‐ray diffraction, scanning electron microscopy, and transmittance as a function of wavelength. The effect of heat treatment in various environments on the structural, electrical, and optical properties has been investigated. Effect of a new annealing ambient, cracked ammonia (reducing atmosphere), on the reactively sputtered oxide films is being reported for the first time. Cracked ammonia was found to be very effective and cheap and resulted in films of high quality (electrical and optical) with good structural properties...

Structural and electrical properties of rf‐sputtered amorphous barium titanate thin films

Structural and electrical properties of rf‐sputtered amorphous BaTiO3 thin films grown on water‐cooled substrates have been investigated. The dielectric and electrical properties have been studied for films grown under varying sputtering gas composition (Ar+O2 gas mixtures) as a function of film thickness, frequency, and temperature. As‐grown films were amorphous in nature and highly transparent. Post‐deposition annealing had no discernible effect either on film structure or dielectric properties, and there was no evidence of ferroelectricity. Films sputtered in pure argon showed a dielectric constant e’∼12 with little dependence on frequency (0.1–100 kHz) over the temperature range 0–75 °C. The dielectric properties were a function of film thickness and the percentage of oxygen in the sputtering gas during growth. The thickness‐dependent dielectric properties of amorphous BaTiO3 thin films on conducting glass substrates could be satisfactorily explained by a model based on the existence of electrode barr...

Enhanced electro-optical properties in gold nanoparticles doped ferroelectric liquid crystals

Influential electro-optical and textural properties in the smectic C* phase have been observed using gold nanoparticles (Au NPs) in ferroelectric liquid crystals (FLCs). An application of mere 0.1V brings fivefold increase in optical tilt and doping creates a strong intrinsic field inside the sample generating high tilt and a reproducible observation of memory effect. The lowering of threshold voltage and the enhanced optical contrast is probably due to the interaction of electron wave oscillation in Au NPs with the incident light traversing through the FLC molecules.

H2S gas sensing mechanism of SnO2 films with ultrathin CuO dotted islands

H2S gas interaction mechanisms of sputtered SnO2 and SnO2–CuO bilayer sensors with a varying distribution of the Cu catalyst on SnO2 are studied using Pt interdigital electrodes within the sensing film. Sensitivity to H2S gas is investigated in the range 20–1200 ppm. Changes induced on the surface, the SnO2–CuO interface, and the internal bulk region of the sensing SnO2 film upon exposure to H2S have been analyzed to explain the increasing sensitivity of three different sensors SnO2, SnO2–CuO, and SnO2 with CuO islands. SnO2 film covered with 0.6 mm diameter ultrathin (∼10 nm) CuO dots is found to exhibit a high sensitivity of 7.3×103 at a low operating temperature of 150 °C. A response speed of 14 s for 20 ppm of H2S, and a fast recovery time of 118 s in flowing air have been measured. The presence of ultrathin CuO dotted islands allow effective removal of adsorbed oxygen from the uncovered SnO2 surface due to spillover of hydrogen dissociated from the H2S–CuO interaction, and the spillover mechanism is ...

Nanoporous cerium oxide thin film for glucose biosensor

Nanoporous cerium oxide (CeO(2)) thin film deposited onto platinum (Pt) coated glass plate using pulsed laser deposition (PLD) has been utilized for immobilization of glucose oxidase (GOx). Atomic force microscopy studies reveal the formation of nanoporous surface morphology of CeO(2) thin film. Response studies carried out using differential pulsed voltammetry (DPV) and optical measurements show that the GOx/CeO(2)/Pt bio-electrode shows linearity in the range of 25-300 mg/dl of glucose concentration. The low value of Michaelis-Menten constant (1.01 mM) indicates enhanced enzyme affinity of GOx to glucose. The observed results show promising application of the nanoporous CeO(2) thin film for glucose sensing application without any surface functionalization or mediator.

Synthesis of photoconducting ZnO nano-needles using an unbalanced magnetron sputtered ZnO/Zn/ZnO multilayer structure

The synthesis of ZnO nano-needles using unbalanced magnetron sputtering is reported. A multilayer structure comprised of ZnO(50 nm)/Zn(20 nm)/ZnO(2 µm) was grown on a stainless steel substrate without substrate heating. The growth of ZnO nano-needles was observed on the surface of the multilayer structure after post-annealing treatment at 300–400 °C. The nano-needles were distributed randomly over the entire surface and had an average diameter of 20 nm; their length varied from 2 to 5 µm. The ultra-thin Zn layer (20 nm) in the multilayer structure is attributed to act as a nucleating centre and it activates the coalescence process for the growth of ZnO nano-needles. The ZnO nano-needles showed enhanced ultraviolet photoresponse with an initial fast rise and decay. The origin of the photoconductivity is due to the bulk related process. Results show the myriad application of ZnO nano-needles in ultraviolet light detection.

Highly sensitive ultraviolet detector based on ZnO/LiNbO3 hybrid surface acoustic wave filter

Fabrication of a highly-sensitive UV detector based on the surface-acoustic-wave (SAW) principle is reported. The output voltage of the SAW oscillator constructed with a ZnO/LiNbO3 hybrid SAW filter was found to decrease linearly with increasing UV light intensity, and a very low intensity UV light of 10 μW/cm2 was detected easily. Our results show its potential use in wireless UV measurement systems.