K. Narasimha Rao

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10−2 ω-cm to 3.57 × 10−3 ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10−1 to 1.69 × 10−2 ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10−4 ω-cm, which was deposited at 350°C with 0.26 g of SbCl3 and 4 g of SnCl4 (SbCl3/SnCl4 = 0.065).Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.

Influence of annealing temperature on Raman and photoluminescence spectra of electron beam evaporated TiO2 thin films

Titanium dioxide (TiO(2)) thin films were deposited on fused quartz substrates by electron beam evaporation method at room temperature. The films were annealed at different temperatures in ambient air. The surface morphology/roughness at different annealing temperatures were analyzed by atomic force microscopy (AFM). The crystallinity of the film has improved with the increase of annealing temperature. The effect of annealing temperature on optical, photoluminescence and Raman spectra of TiO(2) films were investigated. The refractive index of TiO(2) films were studied by envelope method and reflectance spectra and it is observed that the refractive index of the films was high. The photoluminescence intensity corresponding to green emission was enhanced with increase of annealing temperature. The peaks in Raman spectra depicts that the TiO(2) film is of anatase phase after annealing at 300°C and higher. The films show high refractive index, good optical quality and photoluminescence characteristics suggest that possible usage in opto-electronic and optical coating applications.

Properties of ion assisted deposited titania films

Thin films of titanium dioxide have been deposited using ion assisted deposition with oxygen ions in the energy range 100–500 eV and current densities up to 100 μA/cm2. It has been observed that the refractive index of the films increases up to 300 eV and the extinction coefficient increased only nominally up to 300 eV. Optical band gap calculations have shown a strong dependence of the gap on the energy of incident ions. Beyond a critical energy and current density of the ions the refractive index and extinction coefficient of the films start deteriorating. It has also been found that beyond the critical values the optical band gap value decreases. The maximum refractive index obtained was 2.49 at an energy of 300 eV and 50 μA/cm2 current density. Post‐deposition annealing of the films at 500 °C resulted in a slight increase in refractive index without affecting the extinction coefficient. X‐ray diffraction studies revealed a monophasic anatase structure in these films.

Influence of surfactant and annealing temperature on optical properties of sol-gel derived nano-crystalline TiO2 thin films.

Titanium dioxide thin films have been synthesized by sol-gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 degrees C. The influence of surfactant and annealing temperature on optical properties of TiO(2) thin films has been studied. Optical constants and film thickness were estimated by Swanepoels (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO(2) films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO(2) films was estimated by Taucs method at different annealing temperature.

Optical properties of ion assisted deposited zirconia thin films

The nature of the dependence of refractive index, extinction coefficient, and packing density of zirconia films prepared by ion assisted deposition on the energy and current density of ions has been investigated. A broad beam Kaufman ion source has been used to generate oxygen ions in the energy range 100–700 eV and current densities up to 220 µA/cm2. It has been found that the refractive index increases steadily up to an energy of 500 eV beyond which there is a nominal decrease. The highest index obtained was 2.21 at an energy of 500 eV and a current density of 220 µA/cm2. Similarly, with an increase in the current density the refractive index increases initially and seems to saturate beyond a certain critical value dependent on the ion energy. The extinction coefficient was low up to an energy of 300 eV showing a marked increase thereafter. The extinction coefficient was also found to increase at high ion current densities and energies. A critical ion energy and current density beyond which the refractive index as well as the extinction coefficient of these films start deteriorating has been observed.

Optical, dielectric and morphological studies of sol-gel derived nanocrystalline TiO2 films.

Nanocrystalline TiO(2) films have been synthesized on glass and silicon substrates by sol-gel technique. The films have been characterized with optical reflectance/transmittance in the wavelength range 300-1000 nm and the optical constants (n, k) were estimated by using envelope technique as well as spectroscopic ellipsometry. Morphological studies have been carried out using atomic force microscope (AFM). Metal-Oxide-Silicon (MOS) capacitor was fabricated using conducting coating on TiO(2) film deposited on silicon. The C-V measurements show that the film annealed at 300 degrees C has a dielectric constant of 19.80. The high percentage of transmittance, low surface roughness and high dielectric constant suggests that it can be used as an efficient anti-reflection coating on silicon and other optical coating applications and also as a MOS capacitor.

Studies of the optical and structural properties of ion-assisted deposited Al2O3 thin films

Abstract The optical and structural properties of Al 2 O 3 films produced by oxygen-ion assisted deposition (IAD) have been investigated as a function of ion energy (300–1000 eV), ion current density (50–220 μA cm −2 ), and substrate temperature (ambient-300°C). It is observed that films prepared by IAD with the substrates maintained at elevated temperatures show the best properties. The maximum refractive index obtained was 1.73 for films deposited at 1000 eV, 50 μA cm −2 and 300°C. Teh refractive index decreased with the increase in ion current density for ion energies exceeding 300 eV with absorption still being negligible. As-deposited films prepared, with or without ion bombardment, were amorphous. Films deposited without ions and annealed at 800°C in air for 12 h were σ - alumina , whereas those deposited at 1000 eV ion energy, 220 μA cm −2 ion current density and annealed at the same temperature for the same period were found to be α - alumina .

A comparative study of the optical properties of zirconia thin films prepared by ion-assisted deposition

Abstract Thin films of zirconia have been prepared using ion-assisted deposition over a wide range of ion energies from 0 to 700 eV and their optical properties such as refractive index and absorption investigated. The ions were produced using two different ion sources: (1) a Heitmann-type low energy source; (2) a Kaufman-type broad beam ion source to produce ions in the energy range 100–700 eV. It was observed that the refractive index value increased with increasing ion energy. However, the extinction coefficient showed lower values at lower energies than at higher energies. A bulk-like value of 2.2 for the refractive index at a wavelength of 650 nm has been obtained at 500eV energy. The absorption at this energy is fairly high (0.008), but films with negligible absorption have been obtained at lower energies.

Optical properties of ion assisted deposited CeO2 films

Single layer films of

Optical, electrical and dielectric properties of TiO2–SiO2 films prepared by a cost effective sol–gel process

Ce0_2