C.V. Deshpandey

Preparation and properties of cubic boron nitride coatings

Cubic boron nitride (CBN) has attracted a great deal of interest in recent years for its unique mechanical and optical properties. Many physical as well as chemical vapor deposition processes have been explored to synthesize CBN coatings. These techniques, however, suffer limitations owing to the requirements of high substrate temperature and/or the necessity of using toxic starting materials. We have developed a new technique where CBN films can be prepared by evaporating boric acid in NH3 plasma. CBN films have been deposited at substrate temperatures as low as 450°C. Structure and optical and electrical characteristics of the films clearly demonstrate the simple cubic phase in the coatings. These results are presented in this paper.

Synthesis of cubic boron nitride films by activated reactive evaporation of H3BO3

Abstract Hard cubic boron nitride films for wear-and-tear applications have been prepared by activated reactive evaporation of H3BO3 in the presence of an NH3 plasma. The plasma was created by electrons emitted from a resistively heated filament and an anode. It was enhanced by an external magnetic field (about 60 G). H3BO3 was evaporated from a molybdenum boat in NH3 at a pressure of 4.5×10-2 Pa. The substrates were maintained at 450°C during evaporation and a typical rate of deposition of the boron nitride films was found to be 150 nm min-1. The films were characterized by electron diffraction, electron microscopy. Auger electron spectroscopy, IR spectra, optical reflectance and transmittance, microhardness and adhesion measurements. The f.c.c. phase of boron nitride was identified. The microstructure consisted of randomly oriented crystallites with an average grain size of 25 nm. Measurements of the reflectance R and the transmittance T suggest an optical gap of 3.64 eV. The films were found to be highly adherent and to have a microhardness of about 2128 kgf mm-2.

Structure-property relationships in microlaminate TiC/TiB2 condensates

Abstract This is the fourth of the series of papers on microlaminate materials prepared by evaporation techniques. The first two papers dealt with Cu/Ni, Cu/Fe, Ti/Ni and Cr/Cu microlaminate condensates, which are metal/metal systems, and the third dealt with the metal/ceramic system Ni/TiC. In this paper we present the results of our investigations on structure-property relationships in the ceramic/ceramic microlaminate composite TiC/TiB 2 . The composites were prepared at the Paton Electric Welding Institute and studied at the University of California, Los Angeles. The thickness of the composite sheet was 0.25–0.30 mm and the lamina thickness was varied in the range of 0.15–5μm. The microstructure and phases present were studied by microscopic and diffraction techniques whereas bend tests were used to study the mechanical properties.

Microstructure and hardness of Ti(C, N) coatings on steel prepared by the activated reactive evaporation technique

Abstract In view of the potential demand for wear-resistant coatings deposited at low substrate temperatures for applications in the cutting tool industry, titanium carbonitride films were prepared by the activated reactive evaporation technique on high speed steel substrates. Titanium was evaporated in C2H2N2 plasmas of various compositions ranging from pure C2H2 to pure N2, i.e. in C2H2 with 0, 30, 50, 70 and 100 vol.% N2. Knoop hardness values (at 50 gf load) were obtained both on top and in the cross section of each deposit and ranged from 2200 to about 5900, reflecting the variations in chemical composition and microstructure of the films. X-ray diffraction, transmission electron microscopy and scanning transmission electron microscopy analyses were performed to reveal those microstructural features of importance to the coating properties, i.e. phase composition, grain morphology and defect distribution (in particular, void and crack formations).

Preparation and properties of Al2O3 films by d.c. and r.f. magnetron sputtering

Abstract The reactive magnetron sputtering of aluminium in Ar-O2 mixtures was investigated to determine the conditions for preparing oxide films with low optical absorptance as needed for optical use. Both d.c. and r.f. glow discharge excitation were used. The effect of the discharge O2 content, at a given power input, on the film growth rate and the optical reflectance, transmittance, absorptance and refractive index were determined. Aluminium oxide films with refractive indices between 1.6 and 1.62 and absorptances of 0.1%–1% for films 600 A thick were most conveniently prepared by reactive d.c. magnetron sputtering.

Plasma assisted deposition techniques and synthesis of novel materials

Abstract Various industrial applications have been found for plasma assisted deposition processes in the synthesis of a variety of compound films. These include dielectric, metallic and semiconducting films for microelectronics, optics and optoelectronics, as well as hard carbides and nitrides for cutting and forming tools, sulfides for solid lubricants and solid state batteries, etc. The uniqueness of plasma assisted deposition processes lies in their ability to synthesize complex films at relatively low substrate temperatures. These processes enable film properties to be varied over a wide range by control of the plasma conditions e.g. electron density, energy and distribution function. Therefore, plasma assisted deposition processes have attracted a great deal of interest in recent years. We present a review of plasma assisted deposition techniques currently used in industry, in terms of their potential and their limitations for synthesis of novel materials such as diamond, cubic boron nitride, etc. Results of experimental work in our laboratory are also discussed.

Deposition of tin-doped indium oxide films by a modified reactive magnetron sputtering process

Abstract It has been difficult to deposit high quality indium tin oxide (ITO) films onto large area polymeric substrates that cannot be heated (over 40–50 °C) during deposition or subjected to post-deposition annealing. We have developed a modified process based on reactive magnetron sputtering of a metallic indium tin alloy target to deposit good quality ITO films with deposition rates as high as 4A s-1 at a target-substrate distance of 10 in. Films with sheet resistance less than 10 Ω/□ and integrated visible transmission greater than 85% have been deposited using this process onto 12 in 12 × 12 in polymeric substrates at ambient temperature. A detailed description of the above process with an emphasis on obtaining control over the properties and reproducibility of good quality ITO films using this technique is presented in this paper.

Preparation and properties of TiC/Ni microlaminates☆

Abstract This is the fifth paper in a series of papers on microlaminate composite materials prepared by evaporation techniques. Earlier studies dealt with metal/ metal, ceramic/ceramic and metal/ceramic microlaminate condensates. This investigation is an extension of the earlier work on metal/ceramic (Ni/TiC) composites. The relationship between the ultimate tensile strength and the laminate layer thickness at a constant metal-to-ceramic ratio is studied. The nickel layers were produced by direct evaporation and the TiC layers were produced by activated reaction evaporation. The microstructure and phase analysis were studied using microscopy and X-ray diffraction techniques. Tensile tests were carried out at room temperature and at 600 °C on sheet specimens. The results revealed that the strength increased as the laminate layer thickness decreased.

Auger electron spectroscopy and Rutherford backscattering spectroscopy studies of TiN and TiC coatings prepared by the activated reactive evaporation process

Abstract TiN x and TiC x films were deposited by the activated reactive evaporation process under different process conditions. The films were studied by Auger electron spectroscopy and Rutherford backscattering spectroscopy (RBS); standards were used for both techniques. The RBS techniques showed low sensitivity to carbon and nitrogen when 1.8 MeV He + ions were used. The sensitivity was enhanced by using 1.5 MeV H + ions, but the resulting non-Rutherford scattering necessitated the use of standards although RBS is potentially a standardless method. A correlation was found between the chemical composition of TiN x and TiC x films and the partial pressures of N 2 and C 2 H 2 respectively.

Electrical resistance drift of molybdenum silicide thin film temperature sensors

For a thermometer to be of practical use, its accuracy of temperature indication must be within a tolerable range. In this paper, patterned molybdenum disilicide (MoSi2) thin film temperature sensors were fabricated to study their thermoresistance, i.e. resistance vs. temperature (R-T) characteristics. The R-T characteristic of MoSi2 thin films exhibits a positive deviation from linearity (termed “superlinearity”) instead of showing a simple linearity as for most metals. This superlinear behavior was attributed to thermal expansion and the consequent decrease in the Debye characteristic temperature of MoSi2. For long-term duration at elevated temperatures, the variation in thickness and composition of the sensor film due to oxidation and other factors may produce drift in the electrical resistance. In this study, the electrical resistance drifts of the sensors as a function of time at temperatures of 1200, 1300 and 1350 °C are presented. For the sensor film tested at 1300 °C, the resistance drift due to the thickness change of the sensor layer was well corrected with the help of an analysis of the oxidation rate of the sensor material. On the other hand, the in-depth composition profile analyzed by Auger electron spectroscopy (AES) indicated no significant composition variation, implying that we could neglect the correction factor for the composition variation in the present study. After the thickness factor was corrected for, a minor drift was still observed; this was also found for the same sensor film tested in an Ar ambient. The exact source of the minor drift is not well understood; further investigations are required.