Sharmistha Anwar

Thermal stability studies of tungsten nitride thin films

Superior mechanical properties, such as hardness of high level along with thermal stability are of great technological interests for cutting tools and other industrial applications. In this work, we present performance and stability of tungsten nitride (WN) film at a wide temperature range (RT – 600°C). WN films were deposited on silicon (100) substrates using reactive RF magnetron sputtering. The deposited samples were annealed at 200, 400 and 600°C for 2 h. Structural, electrical and mechanical properties of the films were analysed via X-ray diffraction, four-probe resistivity and nano-indentation test, respectively. XRD results show the formation of pure W2N crystalline phase. The change in microstructural parameters were investigated and found to be varying with annealing temperature. The electrical measurement result shows the decrease in resistivity with an increase in annealing temperature. Nano-indentation experiments reveal that the mechanical behaviour (hardness and elastic modulus) at different load are quite stable in the studied temperature range.

Coupling of charge carriers with magnetic entropy for power factor enhancement in Mn doped Sn1.03Te for thermoelectric applications

Despite being a prospective thermoelectric (TE) material, SnTe has limited applicability due to the very high ‘hole’ concentration arising from ‘Sn’ vacancies. Engineering of multiple valence bands with the addition of extra ‘Sn’ and isovalent doping is a well-established strategy for enhancing TE properties. Here, we report a new approach utilizing magnetism to try to enhance the TE properties. The magnetic and TE properties of Mn doped self-compensated Sn1.03Te were studied in the context of its dilute magnetic nature. A systematic (i) increment of magnetic moments and weak ferromagnetism leading to coupling of charge carriers, (ii) increase in effective thermal mass of charge carriers and (iii) overall enhancement in power factor have been observed and analyzed based on magnetization, heat capacity and high temperature transport measurements. At low temperatures, weak ferromagnetism is generated with Mn doping in otherwise diamagnetic Sn1.03Te, thus giving system magnetic entropy and structural disorder, which leads to a modified TE transport. The enhancement in power factor for Sn0.93Mn0.1Te from Sn1.03Te has been explained based on magnetic moments, the anomalous Hall effect, high effective thermal mass and magnetic entropy.

Evaluating the microstructure and mechanical performance of sputtered TiAlBN nanocomposite coating

We report here the microstructural and mechanical properties of nanocrystalline (nc) Titanium Aluminium Nitride (TiAlN) embedded in nanocrystalline Boron Nitride (BN) nanocomposite films. The coatings were deposited on Si substrate using reactive magnetron co-sputtering by varying BN power. Coatings were characterized by using grazing incident X-ray diffraction (GIXRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and nanoindentation. GIXRD showed the formation of cubic Ti3AlN and hexagonal BN phase in the coating. Variation in structure and target power of BN influence the mechanical property of the coating. Mechanical property increases with power up to 100W, then decrease with further increase in power.

Study of nickel interlayer thickness effect on WN/Ni multilayer thin film

Tungsten nitride-Nickel (WN/Ni) multilayer thin films were prepared using reactive magnetron sputtering by varying the Ni interlayer thickness. Microstructure and phase composition were examined using FESEM/EDAX and GIXRD respectively. The mechanical property of the multilayers was calculated using Berkovich nanoindenter. GIXRD showed well defined peaks of W2N phase. Cross-sectional FESEM confirms the alternate layers of WN and Ni having uniform thickness. Mechanical properties showrd that the hardness decreases as the thickness of the soft Ni layer decreases.

Development of nc-W2N/a-Si3N4 hard coating

In this work, the pure nc-W2N and nc-W2N/a-Si3N4 nanocomposite films were deposited at 200°C substrate temperature by magnetron sputtering. The effect of Si3N4 target power on microstructural and mechanical properties of the films were studied. The XRD results showed the formation of cubic nc-W2N in both pure W2N and nc-W2N/a-Si3N4 film. A significant broadening of (111) reflection was present in nc-W2N/a-Si3N4 film with an increase in Si3N4 power. The broadening of peaks suggested a decrease in the average crystallite size (approximately 21 to 2 nm) in the films. Surface morphology showed that grains of W2N were diminished by amorphous Si3N4 with an increase in Si3N4 target power (50-90W). Elemental analysis confirms the presence of W, Si and N elements in the films. The hardness and elastic modulus were improved and found optimum at 50W then reduced at 90W Si3N4 power. The highest hardness and elastic modulus achieved were 22.13 GPa and 263.04 GPa respectively.

Structural and mechanical properties analysis of sputtered W2N/Ni multilayered thin films

In this work a combination of ceramic (Tungsten nitride) with ductile (Nickel), multilayer coatings were deposited on Si (100) substrates by DC magnetron sputtering technique. A series of multilayers were deposited keeping all deposition parameters constant except number of bilayer in similar thickness level. In order to keep deposition time/thickness constant, we have varied number of bilayer of different thickness. Structural characterizations were done by using GIXRD, and FESEM with EDAX. From GIXRD, presence of crystalline W2N phase was confirmed. Existence of alternative layers of tungsten nitride and nickel were revealed from FESEM images. EDAX confirmed the presence of tungsten, nitrogen, and nickel. Mechanical properties of thin films were studied by Nano indentation test. Mechanical properties were found to be influenced with geometrical factor like thickness ratio of ceramic to metal layer in a bilayer arrangement.