Ellipsometry as a Sensitive Technique to Probe film -Substrate Interfaces: Al2O3 on Si(100)

An attempt has been made to study the film-substrate interface by using a sensitive, non- conventional tool. Because of the prospective use of gate oxide in MOSFET devices, we have chosen to study alumina films grown on silicon. Film-substrate interface of alumina grown by MOCVD on Si(100) was studied systematically using spectroscopic ellipsometry in the range 1.5-5.0 eV, supported by cross-sectional SEM, and SIMS. The (ε1,ε2) versus energy data obtained for films grown at 600°C, 700°C, and 750°C were modeled to fit a substrate/interface/film “sandwich”. The experimental results reveal (as may be expected) that the nature of the substrate -film interface depends strongly on the growth temperature. The simulated (ε1,ε2) patterns are in excellent agreement with observed ellipsometric data. The MOCVD precursors results the presence of carbon in the films. Theoretical simulation was able to account for the ellipsometry data by invoking the presence of “free” carbon in the alumina films.

Effect of annealing temperature on electrical and nano-structural properties of sol-gel derived ZnO thin films

Zinc oxide (ZnO) thin films have been prepared on silicon substrates by sol-gel spin coating technique with spinning speed of 3,000 rpm. The films were annealed at different temperatures from 200 to 500 A degrees C and found that ZnO films exhibit different nanostructures at different annealing temperatures. The X-ray diffraction (XRD) results showed that the ZnO films convert from amorphous to polycrystalline phase after annealing at 400 A degrees C. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on pre-cleaned silicon (100) substrates and electrical properties such as current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics were studied. The electrical resistivity decreased with increasing annealing temperature. The oxide capacitance was measured at different annealing temperatures and different signal frequencies. The dielectric constant and the loss factor (tan delta) were increased with increase of annealing temperature.

SOS films and interfaces: chemical aspects

The possible chemical reactions that take place during the growth of single crystal films of silicon on sapphire (SOS) are analyzed thermodynamically. The temperature for the growth of good quality epitaxial films is dependent on the extent of water vapor present in the carrier gas. The higher the water vapor content the higher the temperature needed to grow SOS films. Due to the interaction of silicon with sapphire at elevated temperatures, SOS films are doped with aluminum. The extent of doping is dependent on the conditions of film growth. The doping by aluminum from the substrate increases with increasing growth temperatures and decreasing growth rates. The equilibrium concentrations of aluminum at the silicon-sapphire interface are calculated as a function of deposition temperature, assuming that SiO2 or Al6Si2O13 are the products of reaction. It is most likely that the product could be a solid solutio n of Al2O3 in SiO2. The total amount of aluminum released due to the interaction between silicon and sapphire will account only for the formation of not more than one monolayer of reaction product unless the films are annealed long enough at elevated temperatures. This value is in good agreement with the recently reported observations employing high resolution transmission electron microscopy.

Optical, electrical and dielectric properties of TiO(2)-SiO(2) films prepared by a cost effective sol-gel process

Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (1 0 0) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200 degrees C for their possible use in optoelectronic applications. (C) 2011 Elsevier B.V. All rights reserved.

The influence of Zr layer thickness on contact deformation and fracture in a ZrN-Zr multilayer coating

In order to understand the influence of ductile metal interlayer on the overall deformation behavior of metal/nitride multilayer, different configurations of metal and nitride layers were deposited and tested under indentation loading. To provide insight into the trends in deformation with multilayer spacings, an FEM model with elastic-perfect plastic metal layers alternate with an elastic nitride on top of an elastic-plastic substrate. The strong strain mismatch between the metal and nitride layers significantly alters the stress field under contact loading leading to micro-cracking in the nitride, large tensile stresses immediately below the contact, and a transition from columnar sliding in thin metal films to a more uniform bending and microcracking in thicker coatings.

Optical, electrical and structural characterization of ZnO:Al thin films prepared by a low cost sol-gel method

ZnO:Al thin films were prepared on glass and silicon substrates by the sol-gel spin coating method. The x-ray diffraction (XRD) results showed that a polycrystalline phase with a hexagonal structure appeared after annealing at 400 degrees C for 1 h. The transmittance increased from 91 to about 93% from pure ZnO films to ZnO film doped with 1 wt% Al and then decreased for 2 wt% Al. The optical band gap energy increased as the doping concentration was increased from 0.5 wt% to 1 wt% Al. The metal oxide semiconductor (MOS) capacitors were fabricated using ZnO films deposited on silicon (100) substrates and electrical properties such as current versus voltage (I-V) and capacitance versus voltage (C-V) characteristics were studied. The electrical resistivity decreased and the leakage current increased with an increase of annealing temperature. The dielectric constant was found to be 3.12 measured at 1 MHz. The dissipation value for the film annealed at 300 degrees C was found to be 3.1 at 5 V. (C) 2011 Elsevier Ltd. All rights reserved.

Bioactivity and mechanical properties of nickel-incorporated hydrogenated carbon nanocomposite thin films

In this paper, the influence of nickel incorporation on the mechanical properties and the in vitro bioactivity of hydrogenated carbon thin films were investigated in detail. Amorphous hydrogenated carbon (a-C : H) and nickel-incorporated hydrogenated carbon (Ni/a-C : H) thin films were deposited onto the Si substrates by using reactive biased target ion beam deposition technique. The films' chemical composition, surface roughness, microstructure and mechanical properties were investigated by using XPS, AFM, TEM, nanoindentation and nanoscratch test, respectively. XPS results have shown that the film surface is mainly composed of nickel, nickel oxide and nickel hydroxide, whereas at the core is nickel carbide (Ni3C) only. The presence of Ni3C has increased the sp(2) carbon content and as a result, the mechanical hardness of the film was decreased. However, Ni/a-C : H films shows very low friction coefficient with higher scratch-resistance behavior than that of pure a-C : H film. In addition, in vitro bioactivity study has confirmed that it is possible to grow dense bone-like apatite layer on Ni/a-C : H films. Thus, the results have indicated the suitability of the films for bone-related implant coating applications. Copyright (C) 2011 John Wiley & Sons, Ltd.

Simple coating technique for 2-dimensional zinc oxide nanostructure

We report a novel and simple solution-based technique for depositing 2-D zinc oxide platelets at low temperature. Nanoplatelets that were mostly a-oriented associated with the Lotgering orientation factor of 0.65 were obtained by locating a glass substrate at a distance of about 5cm over the aqueous vapour of the boiling precursor. Experiments were carried out to optimize the coating parameters by placing the substrate at different positions, durations and the pH of the precursor. The X-ray diffraction studies confirmed the structure associated with the crystallites to be wurzite. The different morphology of the zinc oxide films and blue light emission were observed using scanning electron microscopy and fluorescence spectroscopy respectively.

Influence of Sn doping on structural, optical and electrical properties of ZnO thin films prepared by cost effective sol-gel process

Tin (Sn) doped zinc oxide (ZnO) thin films were synthesized by sol-gel spin coating method using zinc acetate di-hydrate and tin chloride di-hydrate as the precursor materials. The films were deposited on glass and silicon substrates and annealed at different temperatures in air ambient. The agglomeration of grains was observed by the addition of Sn in ZnO film with an average grain size of 60 nm. The optical properties of the films were studied using UV-VIS-NIR spectrophotometer. The optical band gap energies were estimated at different concentrations of Sn. The MOS capacitors were fabricated using Sn doped ZnO films. The capacitance-voltage (C-V), dissipation vs. voltage (D-V) and current-voltage (I-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated. The porosity and surface area of the films were increased with the doping of Sn which makes these films suitable for opto-electronic applications. (C) 2012 Elsevier B.V. All rights reserved.

Influence of GaN underlayer thickness on structural, electrical and optical properties of InN films grown by PAMBE

We present an extensive study on the structural, electrical and optical properties of InN thin films grown on c-Al2O3, GaN(130 nm)/Al2O3, GaN(200 nm)/Al2O3 and GaN(4 mu m)/Al2O3 by using plasma-assisted molecular beam epitaxy. The high resolution X-ray diffraction study reveals better crystalline quality for the film grown on GaN(4 mu m)/Al2O3 as compared to others. The electronic and optical properties seem to be greatly influenced by the structural quality of the films, as can be evidenced from Hall measurement and optical absorption spectroscopy. Kane's k.p model was used to describe the dependence of optical absorption edge of InN films on carrier concentration by considering the non-parabolic dispersion relation for carrier in the conduction band. Room temperature Raman spectra for the InN films grown on GaN show the signature of residual tensile stress in contrast to the compressive stress observed for the films grown directly on c-Al2O3. (C) 2012 Elsevier B.V. All rights reserved.

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

Titanium dioxide (TiO2) 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 TiO2 films were investigated. The refractive index of TiO2 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 TiO2 film is of anatase phase after annealing at 300 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.

Optical and structural properties of nanostructured oxide thin films by sol‐gel technique

TiO2 and Al2O3 are commonly used materials in optical thin films in the visible and near‐infrared wavelength region due to their high transparency and good stability. In this work, TiO2 and Al2O3 single, and nano composite thin films with different compositions were deposited on glass and silicon substrates at room temperature using a sol‐gel spin coater. The optical properties like reflectance, transmittance and refractive index have been studied using Spectrophotometer, and structural properties using X‐Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).

Control of magnetization reversal in oriented strontium ferrite thin films

Oriented Strontium Ferrite films with the c axis orientation were deposited with varying oxygen partial pressure on Al2O3(0001) substrate using Pulsed Laser Deposition technique. The angle dependent magnetic hysteresis, remanent coercivity, and temperature dependent coercivity had been employed to understand the magnetization reversal of these films. It was found that the Strontium Ferrite thin film grown at lower (higher) oxygen partial pressure shows Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of pinning and nucleation processes during magnetization reversal is used to explain the type of the magnetization reversal with different oxygen partial pressure during growth. (C) 2014 AIP Publishing LLC.

Optical and structural properties of highly porous shell structured Fe doped TiO2 thin films

TiO2 thin films with 0.2 wt%, 0.4 wt%, 0.6 wt%, and 0.8 wt% Fe were prepared on glass and silicon substrates using sol-gel spin coating technique. The optical cut-off points are increasingly red-shifted and the absorption edge is shifted over the higher wavelength region with Fe content increasing. As Fe content increases, the optical band gap decreases from 3.03 to 2.48 eV whereas the tail width increases from 0.26 to 1.43 eV. The X-ray diffraction (XRD) patterns for doped films at 0.2 wt% and 0.8 wt% Fe reveal no characteristic peaks, indicating that the film is amorphous whereas undoped TiO2 exhibits (101) orientation with anatase phase. Thin films of higher Fe content exhibit a homogeneous, uniform, and nano-structured highly porous shell morphology.

Biocompatible and Antibacterial SnO2 Nanowire Films Synthesized by E-Beam Evaporation Method

In this work, the biocompatibility and antibacterial activities of novel SnO2 nanowire coatings prepared by electron-beam (E-Beam) evaporation process at low temperatures were studied. The nanowire coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) methods. The results of in vitro cytotoxicity and cell proliferation assays suggested that the SnO2 nanowire coatings were nontoxic and promoted the proliferation of C2C12 and L929 cells (> 90% viability). Cellular activities, cell adhesion, and lactate dehydrogenase activities were consistent with the superior biocompatibility of the nanowire materials. Notably, the nanowire coating showed potent antibacterial activity against six different bacterial strains. The antibacterial activity of the SnO2 material was attributed to the photocatalytic nature of SnO2. The antibacterial activity and biocompatibility of the newly developed SnO2 nanowire coatings may enable their use as coating materials for biomedical implants.