Post-deposition Heat-treatment Temperature Research Articles

Microstructural evolution and electrical resistivity of nanocrystalline W thin films grown by sputtering

Tungsten (W) thin films and nanostructures, particularly those having a beta (β)-phase, have attracted a large amount of attention lately because an ultrathin β-phase W film attached to a ferromagnetic layer can reverse the direction of magnetization upon current injection. However, in-depth microstructural studies including the phase transformation in W films as a function of thickness and post-deposition heat treatment temperature are rare. Here, we report the microstructural evolution and the change in the electrical resistivity of W films with thicknesses of 5–40 nm. Microstructural analyses indicate that the β-W is nanocrystalline with a small grain size of about 5 nm, while the alpha (α)-W has a grain size larger than 130 nm with random crystal orientation. We present a state diagram showing the phase of the W film as functions of film thickness and annealing temperature.

An Experimental Approach for Optimizing Coating Parameters of Electroless Ni-P-Cu Coating Using Artificial Bee Colony Algorithm.

This paper aims to present an experimental investigation for optimum tribological behavior (wear depth and coefficient of friction) of electroless Ni-P-Cu coatings based on four process parameters using artificial bee colony algorithm. Experiments are carried out by utilizing the combination of three coating process parameters, namely, nickel sulphate, sodium hypophosphite, and copper sulphate, and the fourth parameter is postdeposition heat treatment temperature. The design of experiment is based on the Taguchi L27 experimental design. After coating, measurement of wear and coefficient of friction of each heat-treated sample is done using a multitribotester apparatus with block-on-roller arrangement. Both friction and wear are found to increase with increase of source of nickel concentration and decrease with increase of source of copper concentration. Artificial bee colony algorithm is successfully employed to optimize the multiresponse objective function for both wear depth and coefficient of friction. It is found that, within the operating range, a lower value of nickel concentration, medium value of hypophosphite concentration, higher value of copper concentration, and higher value of heat treatment temperature are suitable for having minimum wear and coefficient of friction. The surface morphology, phase transformation behavior, and composition of coatings are also studied with the help of scanning electron microscopy, X-ray diffraction analysis, and energy dispersed X-ray analysis, respectively.

Parametric optimization of corrosion and wear of electroless Ni-P-Cu coating using grey relational coefficient coupled with weighted principal component analysis

This research article considers optimization of the four process parameters based on corrosion and wear of electroless Ni-P-Cu coatings. The major characteristics indexes for performance selected to evaluate the processes are corrosion potential (E corr), corrosion current density (I corr) and wear. Among the corresponding four process parameters the first three are coating parameters, viz. concentration of nickel sulphate, concentration of sodium hypophosphite, concentration of copper sulphate and the fourth one is post deposition heat treatment temperature. The corrosion property, i.e. E corr and I corr, has been studied by potentiodynamic polarization test and the wear is measured in terms of wear depth by DUCOM TR-25 multi-tribotester with block on roller arrangement. In this study, the process is intrinsically combined with multiple performance indexes so that grey relational analysis is specially adopted to determine the optimal combination of coating parameters. Moreover, the weighted principal component analysis (WPCA) is applied to evaluate the weighting values corresponding to various performance characteristics so that their relative importance can be properly and objectively described. From the analysis the optimum combination of parameters for corrosion property and the optimum combination of parameters for corrosion and wear together are obtained. The chemical composition, surface morphology and phase behaviour are investigated using energy dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction analysis, respectively.

Optimization of Wear of Electroless Ni-P-Cu Coating Using Artificial Bee Colony Algorithm

This article aims to present an experimental investigation for optimum wear depth of electroless Ni-P-Cu coatings based on four process parameters using artificial bee colony algorithm. Experiments are carried out by utilizing the combination of three coating process parameters viz. nickel sulphate, sodium hypophosphite, copper sulphate and the fourth parameter is post deposition heat treatment temperature. To observe the variation of each parameter with the wear depth, the operating range of each parameter is divided into three equally spaced levels. The design of experiment is based on the Taguchi L 27 experimental design. The measurement of wear is carried out in terms of wear depth using DUCOM TR 25 multi-tribotester apparatus with block on roller arrangement. Here a second order regression equation is obtained for wear depth with the help of Minitab 16 software. The variation of wear depth with the variation of each coating process parameters is observed. The optimum values of each coating process parameters are obtained from the artificial bee colony analysis and the corresponding optimum value of wear depth is also obtained. The surface morphology and composition of coatings are also studied with the help of scanning electron microscopy, energy dispersed X-ray analysis.

Photocatalytic activity and photo-induced superhydrophilicity of sol–gel derived TiO 2 films

TiO 2 thin films have been deposited using various sol–gel routes. X-ray diffraction, ellipsometry, atomic force microscopy, and scanning electron microscopy characterizations show that the film morphology is strongly influenced by the sol nature and post-deposition heat-treatment temperature. Photo-induced properties of the films have been studied in relation to their morphology. In aqueous medium, photocatalytic properties are governed by a migration of photo-generated charge carriers, which occurs through the whole film thickness and closely depends on the film morphology, in particular the crystallization and densification degrees, as well as the primary and secondary particle sizes. Correlations between photocatalytic activity and photo-induced superhydrophilicity show that both properties are influenced by same mechanisms. Photo-wettability mechanisms are less critically influenced by morphologic properties because they only involve a very thin active surface layer.

Structural and Optical Features of Nano-Crystalline Silicon Films Prepared by Pecvd and Rf Magnetron Sputter Techniques

ABSTRACTNano-crystalline Si films were prepared by plasma enhanced chemical vapor deposition (PECVD) and rf-magnetron sputter techniques at various deposition conditions, and the relations of the photoluminescence (PL) phenomena of the films with process variables are discussed. The phase of the films prepared at R.T. by PECVD techniques is somewhere between amorphous and crystalline states, consisting of nano-crystallites of size ranging from 3.2 to 5.3 nm. These films exhibit significant PL intensities near blue light region; the PL peaks shift from 510 to 460 nm with decreasing the reaction gas (SiH4) fraction from 4.7 to 2.0%. The films prepared at 500 °C by PECVD are composed of about 5 and 150 nm crystallites, exhibiting little PL phenomena. The PL intensity of the films prepared by sputter techniques was observed to increase with raising the sputter power and the post-deposition heat-treatment temperature.

Surface Evolution of NiTi and NiTiHf Thin Films

AbstractThe microstructure evolution of Ti-rich NiTi thin films and (TiHf)-rich NiTiHf thin films containing 9at% Hf was investigated. These films were deposited from single NiTi and NiTiHf targets using a DC magnetron sputtering system. Free-standing films were obtained by using single crystal silicon substrates. The thickness of these films was controlled between 10-12 μm. In this investigation, the effects of deposition temperature on the surface and cross-sectional microstructures of these films were studied. Substrate temperature during deposition was varied between 300°C to 700°C at 100°C intervals. The influence of post deposition heat treatment (HT) temperature on the microstructure of these films was also studied. The post deposition HT temperature was varied between 300°C and 800°C at 100°C intervals. Both surface and cross- sectional microstructures were examined using a scanning electron microscope (SEM). The crystallinity and the phases present were determined using x-ray diffractometry. All the as- deposited films were found to be crystalline, even when the substrate temperature was as low as 300°C. Results from the microstructure analysis show that all the films have a relatively fine grain size ranging from 0.2 μm to 2.5 μm, and the grain size increases with increasing substrate deposition temperature. The effect of post deposition HT on grain size was found to be minimal.

Chemical composition, microstructure and magnetic characteristics of yttrium iron garnet (YIG, Ce:YIG) thin films grown by rf magnetron sputter techniques

YIG thin films were grown by rf magnetron sputter techniques. We investigated the effect of post-deposition heat-treatment as well as various deposition parameters such as substrate materials, substrate temperature, sputter power, and sputter gas types on the crystallinity, chemical composition, microstructure and magnetic characteristics of the films. Post-deposition heat-treatment over 750/spl deg/C was applied to crystallize as-prepared amorphous films, and a strong tendency of particular crystallographic planes lying parallel to substrate surface was observed for the heat-treated film on GGG substrate. The chemical composition of the film exhibited a wide range of chemical stoichiometry depending on the oxygen fraction of the sputter gas, and in particular the compositions of the YIG and Ce:YIG films deposited in sputter gas with an oxygen fraction of 20% were Y/sub 2.88/Fe/sub 3.84/O/sub 12/ and Ce/sub 0.24/Y/sub 1.10/Fe/sub 3.50/O/sub 12/, respectively. With raising the temperature of post-deposition heat-treatment from 900/spl deg/C to 1100/spl deg/C, the surface roughness of the film on GGG substrate increased, but coercive force as well as ferromagnetic resonance line width decreased.

Microstructure of KTaxNb1−xO3 Thin Films on MgO (100) Single Crystals

Thin KTaxNb1−xO3 (KTN) films were prepared by deposition of sol–gel precursor solutions on MgO (100) single crystals. Crystal structure and microstructure of the films as a function of processing parameters, such as rate, duration, and temperature of postdeposition heat treatment, were studied. Several techniques such as X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to analyze the films. It was observed that slow heating of KTN films promotes pyrochlore formation while fast‐firing of the films results in predominant formation of the perovskioe phase. In slow‐heated samples, TEM showed randomly oriented pyrochlore crystallites with a vermicular nanostructure of 10–30 nm with an interpenetrating porosity of the same range. In fast‐fired samples, large perovskite pockets with pyrochlore crystallites scattered among them were seen. The large perovskite grains were on the order of 0.1–0.5 μm, irregular in shape and porous. Transmission electron diffraction indicated these were single crystals, and ferroelectric domains were observed in them. Films of up to 1 μm thick were obtained by multiple deposition of the sol–gel KTN. Dense films were achieved when each layer was densified at 750°C for 2 h before the next layer was deposited.

Response study of electron-beam evaporated thin-film tin oxide gas sensors

Thin-film SnO 2 gas sensors are fabricated using an electron-beam evaporation method at pre-optimized substrate temperatures and post-deposition heat-treatment temperature. The response of these sensors is studied for various operating temperatures and reducing gas ambients. Reducing gases used for testing the response are hydrogen, carbon monoxide and methane, as they belong to three distinct chemical families. It is observed that the response of these sensors follows a power-law relationship, with the exponent value always remaining less than one at higher concentrations of reducing gas. Films deposited at 25 and 350 °C and heat treated at 650 °C in O 2 ambient for 2 h are found to be more suitable for sensor application compared to films deposited at intermediate temperatures and heat treated under identical conditions. Further, the response of the sensor is found to deteriorate with a decrease in operating temperature. It is also concluded from the results that a thin-film SnO 2 sensor can be used as a selective sensor for H 2 at either low operating temperature or under very low background concentrations of other reducing gases. Finally, the above-mentioned results are explained using existing physical models.