Harish C Barshilia, Ph D
National Aerospace Laboratories, Surface Engineering Division, Department Member
- Dr. Harish Barshilia works as Chief Scientist & Head of the Department at Surface Engineering Division, CSIR-National... moreDr. Harish Barshilia works as Chief Scientist & Head of the Department at Surface Engineering Division, CSIR-National Aerospace Laboratories, Bangalore, India. Concurrently, he is Prof. of Physical Sciences at AcSIR, New Delhi. His broad areas of research interests include: Nanoscience and Nanotechnology, Solar Energy, Surface Engineering, Optical Coatings, Stealth Coatings, 1-D & 2-D Materials, PVD Coatings, etc. He has published 250 SCI journal papers (h-index: 57), 7 review articles, 33 conference proceeding papers, 6 book chapters (2 by CRC Press). Dr. Barshilia has also authored 16 patents (11 foreign granted), and has delivered 145 invited lectures in India and abroad. Dr. Barshilia was also an Associate Editor of the journal "Nanosci. & Nanotech. Lett.". Google Scholar : goo.gl/hGxLGedit
Zinc oxide (ZnO) is a very promising material for diverse applications in electronics, optoelectronics, spintronics, transparent thin film transistors, high power devices and so on. ZnO and Mn doped ZnO nanostructures with different... more
Zinc oxide (ZnO) is a very promising material for diverse applications in electronics, optoelectronics, spintronics, transparent thin film transistors, high power devices and so on. ZnO and Mn doped ZnO nanostructures with different morphologies were grown via vapour-liquid-solid (VLS) method. Morphological, optical and magnetic behaviour studies were carried out using field emission scanning electron microscope (FE-SEM), micro-Raman, photoluminescence (PL) and vibrating sample magnetometer techniques, respectively. FE-SEM studies revealed the formation of nanowires, nanopillars, nanosheets of ZnO crystals. Raman measurements confirmed the formation of ZnO phase. PL measurements revealed a strong green emission at 536 nm exposing the oxygen deficiency in the ZnO nanostructures. Mn doping was found to affect the morphological, optical and magnetic properties of ZnO nanostructures. Mn doped ZnO nanoneedles exhibited ferromagnetism at room temperature. The significant changes in the properties of ZnO nanostructures after Mn doping are discussed in detail.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited by dc sputtering. The phase purity of TiO 2 was confirmed by Raman spectroscopy, and secondary ion mass spectroscopy was used to analyze the... more
Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited by dc sputtering. The phase purity of TiO 2 was confirmed by Raman spectroscopy, and secondary ion mass spectroscopy was used to analyze the interfacial and chemical composition of ...
Research Interests:
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is... more
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is indispensable for achieving reduced friction between two moving surfaces. The increasing demand for low friction and wear in aerospace and other tribological applications which involve severe sliding conditions and the limitations of fluid lubricants at extreme environmental conditions such as high vacuum, low and high temperature, radiation, etc. gave rise to the need for solid lubricant coatings. Solid lubricants such as transition metal dichalcogenides, soft metals, diamond like carbon films, polymers, etc. have been successful in providing low friction at a sliding interface. However, the use of these coatings is restricted to certain areas of application conditions and environments due to issues related to their structure and properties. In recent years, development of nanostructured coatings has received great attention since they exhibit exotic properties due to nano-scale engineering. Novel coating architectures such as nanocomposites and multilayered coatings have been areas of intense research since these nanostructured solid lubricant coatings exhibit improved tribological properties in combination with other desirable properties such as improved adhesion and hardness over a wide range of environmental conditions. In this review, we have described the deposition and characterization of nanostructured solid lubricant coatings which have great potential for enhancing the properties of traditional solid lubricant coatings. Various methods used for the preparation of the nanostructured solid lubricant coatings have been described in brief. We describe in detail, the structure, microstructure, adhesive strength, mechanical and tribological properties, and thermal stability of sputter deposited nanostructured solid lubricant coatings. We also present the potential applications of nanostructured solid lubricant coatings in aerospace, automotive and other engineering sectors.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445,... more
The properties of spectrally selective solar absorber coatings can be fine-tuned by varying the thickness and composition of the individual layers. We have deposited individual layers of WAlSiN, SiON, and SiO2 of thicknesses ~940, 445, and 400 nm, respectively, for measuring the refractive indices and extinction coefficients using spectroscopic ellipsometer measurements. Appropriate dispersion models were used for curve fitting of Ψ and Δ for individual and multilayer stacks in obtaining the optical constants. The W/WAlSiN/SiON/SiO2 solar absorber exhibits a high solar absorptance of 0.955 and low thermal emissivity of 0.10. The refractive indices and extinction coefficients of different layers in the multilayer stack decrease from the substrate to the top anti-reflection layer. The graded refractive index of the individual layers in the multilayer stack enhances the solar absorption. In the tandem absorber, WAlSiN is the main absorbing layer, whereas SiON and SiO2 act as anti-refle...
Research Interests:
Superalloys such as Nimonic 80A have high strength at elevated temperatures, which make them attractive towards various applications in aerospace industry.
Research Interests:
Abstract The paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0o to 180o. A sensor is comprised of two Wheatstone bridges arranged at 45o to each other. A unique design... more
Abstract The paper presents the development of a novel anisotropic magnetoresistive sensor for measurement of angle in the interval 0o to 180o. A sensor is comprised of two Wheatstone bridges arranged at 45o to each other. A unique design is proposed wherein each resistive element of the Wheatstone bridge was formed with strips of varying widths. It results in a substantial reduction in harmonics errors due to the dispersion of the shape anisotropy field values within each element. The reduced harmonic errors also lead to a drastic reduction of hysteresis error (60 %) and offer better accuracy with a signal amplitude of 18 mV/V even in weak fields of ≤ 80 G. Further, the sensor was employed in the development of a pedal position sensor. The preliminary results of the development are presented, indicating the usability for industrial and automotive applications.
Research Interests:
Research Interests:
Solid particle erosion is an unavoidable problem for gas turbine compressor blades, wind turbines, crude oil pipes, rovers in outer space, and other machine components operated in harsh conditions. Gas turbine components are usually... more
Solid particle erosion is an unavoidable problem for gas turbine compressor blades, wind turbines, crude oil pipes, rovers in outer space, and other machine components operated in harsh conditions. Gas turbine components are usually operated in the temperature range of 100–1400 °C. However, the influence of temperature on the solid particle erosion mechanism has not been studied adequately. In this paper, the influence of temperature on the solid particle erosion properties of metals (Ti6Al4V, SS 304, Al-8011, and Ti/TiN multilayers) and non-metals (Al2O3, fused quartz, and Si) is studied. The erosion tests were conducted in the temperature range of 30–800 °C. The erosion rate of metallic and ionic solids (viz., Ti6Al4V, SS 304, Al-8011, Al2O3, and Ti/TiN multilayers with the thermal expansion coefficient α ≥ 8 μm/°C) initially decreased with increasing temperature and then increased at higher temperatures, whereas for covalently bonded materials such as fused quartz (α = 0.55 μm/°C...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed... more
ABSTRACT Significant research in the past decade has been focused on quantitatively and qualitatively validating potential of solar thermoelectric modules to harness electricity. In the present study, we have experimentally analysed steady-state temperature variation of a spectrally selective solar absorber coating (α = 0.954, ε = 0.13) with variation in solar irradiation flux (concentration ratios = 39, 50 and 65) using Fresnel lens and vacuum enclosure pressure (200 mbar to 900 mbar in steps of 100 mbar). It is observed that the experimental results so obtained go hand in hand with a COMSOL simulation model of the set-up. Further, we have carried out performance analysis of a solar thermoelectric generator (STEG) set-up enclosed in vacuum conditions equipped with Fresnel lens and absorber set-up coupled to Bi2Te3 thermoelectric module array electrically connected in series. The results depict a maximum power output of 0.91 W and a peak efficiency of 2.21% at a hot-side temperature of 642 K.
Research Interests:
High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm × 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures... more
High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm × 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, micro-Raman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I2D/IG ratio = 2 confirmed the presence of the monolayer graphene and the absence of ‘D’ peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene.
Research Interests: Condensed Matter Physics, Materials Science, Raman Spectroscopy, Graphene, Composite Materials, and 9 moreTransmission Electron Microscopy, Chemical Vapor Deposition, Bilayer graphene, X Ray Photoelectron Spectroscopy, Monolayer, Crystallite, Monolayer Graphene, Selective Area Electron Diffraction Pattern, and Hydrogen Flow Rate
Research Interests:
In this paper, we have demonstrated a simple and cost effective HF-vapor phase etching method to fabricate the broadband quasi-omnidirectional antireflective surface on glass substrate. Both-sides etched sodalime glass substrates under... more
In this paper, we have demonstrated a simple and cost effective HF-vapor phase etching method to fabricate the broadband quasi-omnidirectional antireflective surface on glass substrate. Both-sides etched sodalime glass substrates under optimized conditions showed a broadband enhancement in the transmittance spectra with maximum transmittance as high as ~97% at 598 nm. FESEM results confirmed the formation of a graded nanoporous surface, which lowers it refractive index. The etched surface exhibited excellent AR property over a wide range of incidence angles (8°-48°), which is attributed due to the formation of graded porosity. Silicon solar cell covered with plain glass showed Isc of 0.123A and efficiency of 8.76%, while it showed Isc of 0.130A and efficiency of 9.2% when it was covered by etched glass. Furthermore, it exhibited an excellent anti-soiling property as compared to plain glass. All these results show its strong potential in the photovoltaic application.
Research Interests:
ABSTRACT The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of... more
ABSTRACT The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of work stations have enabled microscale machining operations to acquire an edge over other fabrication techniques in various applications such as aerospace, instrumentation, automotive, biomedical, etc. The literature is filled with works done by researchers working in this domain. A significant contribution comes from the works which have been published during the period 1998–2014. The focus of these studies has primarily been on conventional and nonconventional micromachining techniques. Since nonconventional machining operations such as microelectrical discharge machining, laser machining, etc., are not compatible with traditional workpiece materials, conventional micromachining techniques such as micromilling and microdrilling are generally used. However, as of today, there has been no revision on the state of the-art in this field to serve as a reference for the experienced researcher and as a handbook for the newcomer. In this review, we have attempted to summarize the current state of understanding on this topic. A variety of issues which are representative of micromachining operations are critically analyzed and presented. Conventional micromachining operations have been compared with their nonconventional counterparts with respect to performance characteristics such as burr formation, surface integrity, etc., and their advantages and shortcomings have been listed. Meticulous efforts have been taken to address the key challenges faced in typical micromachining operations. Taking the convenience of the reader into consideration, we have presented a bird's-eye view of the various micromachining operations and simulation studies as performed in the last decade. In the last few years, diamond turning operations have gained more importance and are particularly used for machining composite materials and superalloys. This paper gives an insight into these operations apart from providing an outlook for future growth and development of micromachining technology.
Research Interests:
Research Interests:
Research Interests:
Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited by dc sputtering. The phase purity of TiO 2 was confirmed by Raman spectroscopy, and secondary ion mass spectroscopy was used to analyze the... more
Thin films of TiO 2 were grown on n-type Si substrate by thermal oxidation of Ti films deposited by dc sputtering. The phase purity of TiO 2 was confirmed by Raman spectroscopy, and secondary ion mass spectroscopy was used to analyze the interfacial and chemical composition of ...
Research Interests:
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Solid State Physics, Raman Spectroscopy, and 15 moreComposite Materials, Atomic Force Microscopy, Physical Vapor Deposition, Nanocomposite, Sputtering, Magnetron Sputtering, Power Supply, X ray diffraction, Thermal Stability, Microstructures, Elastic Modulus, X Ray Photoelectron Spectroscopy, Sputter Deposition, Direct Current, and Mechanical Property
Abstract We report the controlled fabrication of kinked silicon nanowires (SiNWs) using ethanol mixed facile two-step metal-assisted chemical etching (MACE) method. Accordingly, the kink angle, straight path, and the number of kinks in... more
Abstract We report the controlled fabrication of kinked silicon nanowires (SiNWs) using ethanol mixed facile two-step metal-assisted chemical etching (MACE) method. Accordingly, the kink angle, straight path, and the number of kinks in kinked SiNWs are controlled by varying the volume of ethanol and etching time in high concentrated plating and etching solutions. The silver nanoparticles (AgNPs) during the etching need to travel a critical length (≥1.5 μm) in a vertical direction before the kink formation. The presence of ethanol in etching solution affects the availability of H2O2 and HF at Si/Ag interface and has a major effect on the etching process. The room temperature photoluminescence (PL) emission of kinked SiNWs is tuned from the red region to the blue region by controlling the amount of ethanol in the etching solution. The temporal behaviour of the PL data of the kinked SiNWs has been provided to understand in depth the optical transition processes.
Research Interests:
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is... more
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is indispensable for achieving reduced friction between two moving surfaces. The increasing demand for low friction and wear in aerospace and other tribological applications which involve severe sliding conditions and the limitations of fluid lubricants at extreme environmental conditions such as high vacuum, low and high temperature, radiation, etc. gave rise to the need for solid lubricant coatings. Solid lubricants such as transition metal dichalcogenides, soft metals, diamond like carbon films, polymers, etc. have been successful in providing low friction at a sliding interface. However, the use of these coatings is restricted to certain areas of application conditions and environments due to issues related to their structure and properties. In recent years, development of nanostructured coatings has received great attention since they exhibit exotic properties due to nano-scale engineering. Novel coating architectures such as nanocomposites and multilayered coatings have been areas of intense research since these nanostructured solid lubricant coatings exhibit improved tribological properties in combination with other desirable properties such as improved adhesion and hardness over a wide range of environmental conditions. In this review, we have described the deposition and characterization of nanostructured solid lubricant coatings which have great potential for enhancing the properties of traditional solid lubricant coatings. Various methods used for the preparation of the nanostructured solid lubricant coatings have been described in brief. We describe in detail, the structure, microstructure, adhesive strength, mechanical and tribological properties, and thermal stability of sputter deposited nanostructured solid lubricant coatings. We also present the potential applications of nanostructured solid lubricant coatings in aerospace, automotive and other engineering sectors
Research Interests:
Tungsten disulphide (WS2) is one of the widely used intrinsic low friction materials, which is commonly used in the form of coating. WS2 offers very low coefficient of friction only in non humid conditions. Presence of humidity destroys... more
Tungsten disulphide (WS2) is one of the widely used intrinsic low friction materials, which is commonly used in the form of coating. WS2 offers very low coefficient of friction only in non humid conditions. Presence of humidity destroys this property and restricts its utility. Modifying the structure of WS2 by adding certain metals helps in overcoming this limitation and in addition improves the mechanical properties. Further, deposition technique and processing parameters play a critical role in deciding the properties of a coating. In this work, Cr-WS2 coatings were deposited on silicon and stainless steel substrates using a fourcathode direct current (DC) unbalanced magnetron sputtering system. Effect of substrate bias and WS2 top layer on the lubricating behavior of coatings has been studied. Deposited coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), nanoindentation, and tribometry techniques to a...
Research Interests:
Abstract The conventional methods of obtaining solar selective surfaces for high temperature solar thermal applications involve coating of the substrate by various methods such as physical vapor deposition, plasma spraying, anodization,... more
Abstract The conventional methods of obtaining solar selective surfaces for high temperature solar thermal applications involve coating of the substrate by various methods such as physical vapor deposition, plasma spraying, anodization, etc. The present work is an attempt to enhance the optical properties of metals by heat treatment. The oxide layers formed by annealing of stainless steel 304 (SS 304) enhance the absorptance in the solar spectrum region. Influences of oxidation temperature and oxidation time span on the values of solar absorptance and thermal emittance have been studied. The annealing of SS 304 substrate was carried out in air at 600–900 °C. The time period of annealing plays a crucial role in the amount of oxides formed and thus is a variable parameter. The absorptance values obtained with isothermal oxidation at shorter and longer durations have been compared at a temperature of 900 °C. A cyclic loading approach is also employed to arrive at the optimal absorptance of the samples. It is further used to study the dependency of solar absorptance on the reaction kinetics with respect to varying oxidation time. Under the optimized annealing conditions, heat-treated SS 304 sample exhibited an absorptance of 0.920 and an emittance of 0.37. A plausible model for the high optical absorption in these oxidized surfaces with relatively low thermal emittance is rationalized. High temperature materials such as Inconel and Nimonic have also been subjected to isothermal annealing and the absorptance values were found to be 0.887 and 0.880, respectively.
Research Interests:
Molybdenum-doped diamond-like carbon (Mo-DLC) coatings have been deposited on titanium β-21S alloy (Ti–15Mo–3Nb–3Al–0.2Si) using plasma-enhanced chemical vapor deposition (PECVD) equipped with pulsed-DC magnetron sputtering. Mo contents... more
Molybdenum-doped diamond-like carbon (Mo-DLC) coatings have been deposited on titanium β-21S alloy (Ti–15Mo–3Nb–3Al–0.2Si) using plasma-enhanced chemical vapor deposition (PECVD) equipped with pulsed-DC magnetron sputtering. Mo contents in the deposited coatings have been controlled with an applied sputtering pulse duty cycle. Chemical composition, structure, morphology, and topography have been studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM), respectively. XRD pattern of the coating with highest Mo content shows the presence of carbide phase. Smooth features with low roughness values are observed in low Mo content coating, whereas high Mo content coating shows granular characteristics with a high roughness value. Raman spectra reveal the increased graphitic content for the highest metal concentration in the coatings, wherein the nanohardness is also determined to be...
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
A combination of plasma-enhanced chemical vapor deposition and magnetron sputtering techniques has been employed to deposit chromium-doped diamond-like carbon (DLC) coatings on stainless steel, silicon and glass substrates. The... more
A combination of plasma-enhanced chemical vapor deposition and magnetron sputtering techniques has been employed to deposit chromium-doped diamond-like carbon (DLC) coatings on stainless steel, silicon and glass substrates. The concentrations of Cr in the coatings are varied by changing the parameters of the bipolar pulsed power supply and the argon/acetylene gas composition. The coatings have been studied for composition, morphology, surface nature, nanohardness, corrosion resistance and wear resistance properties. The changes in ID/IG ratio with Cr concentrations have been obtained from Raman spectroscopy studies. Ratio decreases with an increase in Cr concentration, and it has been found to increase at higher Cr concentration, indicating the disorder in the coating. Carbide is formed in Cr-doped DLC coatings as observed from XPS studies. There is a decrease in sp3/sp2 ratios with an increase in Cr concentration, and it increases again at higher Cr concentration. Nanohardness studies show no clear dependence of hardness on Cr concentration. DLC coatings with lower Cr contents have demonstrated better corrosion resistance with better passive behavior in 3.5% NaCl solution, and corrosion potential is observed to move toward nobler (more positive) values. A low coefficient of friction (0.15) at different loads is observed from reciprocating wear studies. Lower wear volume is found at all loads on the Cr-doped DLC coatings. Wear mechanism changes from abrasive wear on the substrate to adhesive wear on the coating.
Research Interests:
Research Interests:
Vanadium oxide thin films were deposited on quartz substrate by pulsed RF magnetron sputtering technique at 400–600 W and subsequently annealed at 100 °C in vacuum (1.5 × 10−5 mbar). Phase analysis, surface morphology and topology of the... more
Vanadium oxide thin films were deposited on quartz substrate by pulsed RF magnetron sputtering technique at 400–600 W and subsequently annealed at 100 °C in vacuum (1.5 × 10−5 mbar). Phase analysis, surface morphology and topology of the films e.g., both as-deposited and annealed were investigated by x-ray diffraction, field emission scanning electron microscopy and atomic force microscopy techniques. X-ray photoelectron spectroscopy (XPS) was employed to understand the elemental oxidation of the films. Transmittance of the films was evaluated by UV–vis-NIR spectrophotometer in the wavelength range of 200–1600 nm. Sheet resistance of the films was measured by two-probe method both for as-deposited and annealed conditions. XPS study showed the existence of V5+ and V4+ species. Metal to insulator transition temperature of the as-deposited film decreased from 339 °C to 326 °C after annealing as evaluated by differential scanning calorimetric technique. A significant change in transmittance was observed in particular at near infrared region due to alteration of surface roughness and grain size of the film after annealing. Sheet resistance values of the annealed films decreased as compared to the as-deposited films due to the lower in oxidation state of vanadium which led to increase in carrier density. Combined nanoindentation and finite element modeling were applied to evaluate nanohardness (H), Young's modulus (E), von Mises stress and strain distribution. Both H and E were improved after annealing due to increase in crystallinity of the film.
Research Interests:
Vanadium oxide-molybdenum oxide (VO-MO) thin (21–475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the... more
Vanadium oxide-molybdenum oxide (VO-MO) thin (21–475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at ~45–50 °C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 °C) vacuum (10−5 mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and e...
Research Interests:
Research Interests:
The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of work... more
The concept of miniaturizing machine tools has received a strong interest in the research community due to their ability to fabricate intricate components. Lower power consumption, higher productivity rate, and smaller sizes of work stations have enabled microscale machining operations to acquire an edge over other fabrication techniques in various applications such as aerospace, instrumentation, automotive, biomedical, etc. The literature is filled with works done by researchers working in this domain. A significant contribution comes from the works which have been published during the period 1998–2014. The focus of these studies has primarily been on conventional and nonconventional micromachining techniques. Since nonconventional machining operations such as microelectrical discharge machining, laser machining, etc., are not compatible with traditional workpiece materials, conventional micromachining techniques such as micromilling and microdrilling are generally used. However, as of today, there has been no revision on the state of the-art in this field to serve as a reference for the experienced researcher and as a handbook for the newcomer. In this review, we have attempted to summarize the current state of understanding on this topic. A variety of issues which are representative of micromachining operations are critically analyzed and presented. Conventional micromachining operations have been compared with their nonconventional counterparts with respect to performance characteristics such as burr formation, surface integrity, etc., and their advantages and shortcomings have been listed. Meticulous efforts have been taken to address the key challenges faced in typical micromachining operations. Taking the convenience of the reader into consideration, we have presented a bird's-eye view of the various micromachining operations and simulation studies as performed in the last decade. In the last few years, diamond turning operations have gained more importance and are particularly used for machining composite materials and superalloys. This paper gives an insight into these operations apart from providing an outlook for future growth and development of micromachining technology.
Research Interests:
In this work, glow discharge continuous wave plasma polymerization technique was used to deposit nanostructured polyaniline (PANI) thin film by varying input power. The radio frequency (RF) used for plasma polymerization was 13.56 MHz and... more
In this work, glow discharge continuous wave plasma polymerization technique was used to deposit nanostructured polyaniline (PANI) thin film by varying input power. The radio frequency (RF) used for plasma polymerization was 13.56 MHz and working pressure was 0.15 mbar. It was found that, changes in the input power can be used to control the properties of the plasma polymerized PANI thin films. Highly cross-linked structure with an increase in chain length was observed from FTIR spectra with input RF power, whereas the film surface morphology was found to be highly uniform, densely packed and smooth from FE-SEM images. The surface roughness of the film was found to increase with RF power. The refractive index and adhesion of the film was found to be increased while the optical band gap and surface energy decreased with input RF power. The plasma polymerized PANI film showed outstanding optical transmission loss properties and proved itself as excellent optical waveguide
Research Interests:
In this study, we demonstrate the enhanced H 2 S sensitivity of cobalt phthalocyanine (CoPc) film by utilizing Ar + O2 plasma treated nanoporous surface formed on polyethylene terephthalate (PET). Field emission scanning electron... more
In this study, we demonstrate the enhanced H 2 S sensitivity of cobalt phthalocyanine (CoPc) film by utilizing Ar + O2 plasma treated nanoporous surface formed on polyethylene terephthalate (PET). Field emission scanning electron microscopy results confirm the formation of nanoporous surface on PET substrate. The gas sensing properties of CoPc film of thickness 30 nm deposited on the plasma treated PET (CoPc-Treated film) were studied at room temperature and compared with CoPc film grown on untreated PET (CoPc-Untreated film). Sensitivity values were found to be ∼900 and 1300% (for 20 ppm) for CoPc-Untreated and CoPc-Treated films, respectively. This enhanced sensitivity is attributed to porous-like surface of CoPc-Treated film, as it provides the large surface area for the gas adsorption as compared to CoPc-Untreated film. The Elovich equation was employed for the chemical adsorption of H 2 S on CoPc-Treated film surface. Moreover, electrical properties of CoPc-Treated film were studied under various bending conditions, which showed its strong potential for making the flexible and light weight gas sensor.
Research Interests:
Vanadium oxide-molybdenum oxide (VO-MO) thin (21–475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the... more
Vanadium oxide-molybdenum oxide (VO-MO) thin (21–475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V2O5, V2O3 and VO2 along with MoO3. Reversible or smart transition was found to occur just above the room temperature i.e., at ~45–50 °C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 °C) vacuum (10 −5 mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films.
Research Interests:
We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial... more
We report the machining characteristics and machinability of a nickel based superalloy in this study. A micro-milling operation is loaded on Nimonic 75 using uncoated and TiAlN coated tungsten carbide micro-end mills. A full factorial design of experiments was devised to optimize the machining conditions to reduce the flank wear on the tool surface. The optimized machining conditions for uncoated micro-tools were found to be a cutting speed (v c) of 13 m/min and a feed rate (f z) of 6 mm/min. Following this, the tools were coated with TiAlN using a semi-industrial four-cathode reactive pulsed direct current unbalanced magnetron sputtering system. Further experiments were then performed using these optimized machining conditions using both uncoated and TiAlN coated micro-tools in order to ascertain the tool wear and surface integrity. The change in geometry of the machined slot was estimated based on the variation in tool radius of the micro-end mill with progression of the operation. A direct comparison was made between the results observed using both uncoated and TiAlN coated tungsten carbide to illustrate the effect of the nanocomposite TiAlN coating. It was seen that TiAlN coated micro-tools exhibited a superior performance as compared to the uncoated ones with respect to tool life and micro-burr formation.
Research Interests:
ITO/Ag/ITO (IAI) multilayer coatings were designed for spectral beam splitter applications and these coatings were deposited on glass substrates by magnetron sputtering method. The thicknesses of the component layers, namely, Ag and ITO... more
ITO/Ag/ITO (IAI) multilayer coatings were designed for spectral beam splitter applications and these coatings were deposited on glass substrates by magnetron sputtering method. The thicknesses of the component layers, namely, Ag and ITO were varied to achieve high visible transmittance, high NIR-IR reflectance and optimum cutoff wavelength. The optimized ITO/Ag/ITO exhibits high visible transmittance (∼88%) and high NIR-IR reflectance (>90%) with an optimum cutoff wavelength (∼900 nm). A novel chemical etching method was used to improve the transmittance of the plain glass substrate. The optimized IAI multilayer coating deposited on single side etched glass substrate resulted in increase in transmittance (∼91%), which is due to the nano-porous morphology of the etched glass substrate. The angular and polarization dependence studies of IAI multilayer coatings were also studied in detail.
Research Interests:
The colored solar-thermal collectors can provide advantages of architectural integration over energy performance. The colour appearance of the solar-thermal collectors can be achieved by increasing the number of layers. W/WAlN/WAlON/Al2O3... more
The colored solar-thermal collectors can provide advantages of architectural integration over energy performance. The colour appearance of the solar-thermal collectors can be achieved by increasing the number of layers. W/WAlN/WAlON/Al2O3 coating, fabricated by DC and RF magnetron sputtering showed a high solar absorptance of 0.948 and the low thermal emittance of 0.08 with a sky blue color appearance. The tandem absorber exhibited excellent long-term thermal stability at 500 °C in air for 150 h. The absorber deposited on SS substrates showed high solar selectivity (α/ε) of 0.918/0.11, even after heat treatment in air up to 500 °C for 100 h. The selective performance of the coating can be stable more than 25 years. The humidity test confirms the significant moisture resistant of the coating. In summary, the new W/WAlN/WAlON/Al2O3 –based coating with its colourful appearance is appropriate to be used in solar thermal collectors.
Research Interests:
Research Interests:
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is... more
Advancements in surface modification technologies have led to the development of various thin coatings aimed at improving the tribological properties of materials in order to reduce losses due to friction and wear. Lubrication is indispensable for achieving reduced friction between two moving surfaces. The increasing demand for low friction and wear in aerospace and other tribological applications which involve severe sliding conditions and the limitations of fluid lubricants at extreme environmental conditions such as high vacuum, low and high temperature, radiation, etc. gave rise to the need for solid lubricant coatings. Solid lubricants such as transition metal dichalcogenides, soft metals, diamond like carbon films, polymers, etc. have been successful in providing low friction at a sliding interface. However, the use of these coatings is restricted to certain areas of application conditions and environments due to issues related to their structure and properties. In recent years, development of nanostructured coatings has received great attention since they exhibit exotic properties due to nano-scale engineering. Novel coating architectures such as nanocomposites and multilayered coatings have been areas of intense research since these nanostructured solid lubricant coatings exhibit improved tribological properties in combination with other desirable properties such as improved adhesion and hardness over a wide range of environmental conditions. In this review, we have described the deposition and characterization of nanostructured solid lubricant coatings which have great potential for enhancing the properties of traditional solid lubricant coatings. Various methods used for the preparation of the nanostructured solid lubricant coatings have been described in brief. We describe in detail, the structure, microstructure, adhesive strength, mechanical and tribological properties, and thermal stability of sputter deposited nanostructured solid lubricant coatings. We also present the potential applications of nanostructured solid lubricant coatings in aerospace, automotive and other engineering sectors.
Research Interests:
Current research problems in the surface coatings technology include development of various thin coatings with exotic properties as part of an effort to modify the surfaces of a variety of engineering materials at lower cost. Among these... more
Current research problems in the surface coatings technology include development of various thin coatings with exotic properties as part of an effort to modify the surfaces of a variety of engineering materials at lower cost. Among these coatings, multilayer/ superlattice coatings have generated a lot interest in the scientific community because of their exotic properties and probable technological applications in diverse fields. This article outlines the latest developments in the field of multilayer coatings. Multilayer coatings of ceramic/ceramic materials are discussed in detail. Characterization techniques such as – X-ray diffraction, transmission electron microscopy, nanoindentation hardness tester, atomic force microscopy, low-angle X-ray reflectivity, potentiodynamic polarization, etc. have been used to discuss the structural and the mechanical properties of the multilayer coatings. We also discuss the thermal stability of the multilayer superlattice coatings.
Research Interests:
Single layer TiN and NbN coatings were deposited on Si (111) and tool steel substrates using a reactive DC magnetron sputtering process. Process parameters were controlled in such a way that cubic phases of TiN and NbN with B1 structure... more
Single layer TiN and NbN coatings were deposited on Si (111) and tool steel substrates using a reactive DC magnetron sputtering process. Process parameters were controlled in such a way that cubic phases of TiN and NbN with B1 structure were formed. Subsequently, TiN/NbN multilayer coatings were deposited at various modulation wavelengths (), that is the bilayer thicknesses. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. Multilayer coatings deposited at 120 Å > > 25 Å showed satellite reflections along (111) principal reflection, thus confirming the formation of superlattice structure. The multilayer coatings exhibited hardness as high as ~4000 kg/mm2, which was about 2 times the rule-of-mixtures value. The AFM images showed that the coatings had a roughness of ~5 nm