Awadesh Mallik | Nanyang Technological University (original) (raw)
Papers by Awadesh Mallik
Coatings
In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively follo... more In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively following thin-film CVD and PVD routes. It has been found that a combined pre-treatment of the silicon base substrate, via argon plasma etching for creating surface roughness and, thereafter, detonation nanodiamond (DND) seeding, helps in the nucleation and growth of well-adherent CVD diamond films with a well-defined Raman signal at 1332 cm−1, showing the crystalline nature of the film. Ti sputtering on such a CVD-grown diamond surface leads to an imprinted bead-like microstructure of the titanium film, generated from the underlying diamond layer. The cross-sectional thickness of the titanium layer can be found to vary by as much as 0.5 µm across the length of the surface, which was caused by a subsequent hydrogen plasma etching process step of the composite film conducted after Ti sputtering. The hydrogen plasma etching of the Ti–diamond composite film was found to be essential for smoothen...
Materials, 2022
Finesse coefficient is one of the most important parameters describing the properties of a resona... more Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.
Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The... more Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The condition under which the formation of sp3 carbon takes place is a metastable one. There is a requirement of seed material to start the formation of diamond phase, and moreover there are substrates which favour its growth. There is still much scope of research in understanding the metastable synthesis of diamond. Such coatings need to be physically characterised and mechanically polished down to very smooth top surface for any meaningful industrial application. The work plan of the present thesis can be divided into six categories: 1. The nucleation and growth of CVD diamond is first investigated using conventional diamond micron-grit suspension seeding of silicon substrates. 2. Secondly, emphasis was given on the detonation nanodiamond (DND) seeding technique for understanding the metastable growth process of the sp3 phase. It was found that CVD growth conditions lead to capillary rise in pressure inside the vacuum chamber, which thereby replicates high pressure high temperature (HPHT) environment, thus contradicts the prevailing knowledge of metastable diamond synthesis of CVD diamond. 3. Such CVD as-grown diamond films were then characterised using different tools, like XRD, Raman, SEM, XPS etc. 4. Since, 915 MHz microwave frequency was used to grow CVD diamond, it led to coating non-uniformity, over large areas. So, such large area diamond deposition characteristics were then necessary to study. 5. Next, polishing was done on such large area diamond coatings with evaluation of its efficacy. 6. Separately, diamond like nanocomposite (DLN) coating was also deposited by a separate PECVD reactor and characterised for knee implant bio-coating application. In the first chapter of the thesis introductory remarks have been made on the issues involving each of the above six subjects. Second chapter describes the experimental techniques adapted in the thesis work. The third chapter discusses the results obtained from these experiments to address each of the above six sub-categories. The final and fourth chapter concludes the thesis work highlighting the important observations of this PhD study.
Engineering Applications of Diamond, 2021
benefits of the human society [11, 12], like making faster and smaller future electronics, quantu... more benefits of the human society [11, 12], like making faster and smaller future electronics, quantum computers, high power lasers, nuclear energy, capturing carbon for reducing its footprint in the environment [13], medical devices for patients [14] or even water purification [15] for a better standard of living (Table 1). This chapter lists some of the engineering applications where the scientific knowledge of the diamond material property has been used to build/design/create something useful for the people on earth.
Trends in biomaterials & artificial organs, 2015
Diamond is considered as high quality bio-ceramic material due to its physical and mechanical pro... more Diamond is considered as high quality bio-ceramic material due to its physical and mechanical properties. Diamond has the highest hardness as well as it is bio-compatible, non-toxic and chemically inert. Different biological cells growing on the diamond surface indicates that diamond does not interfere in cell growth mechanism. Nucleation side of the freestanding diamond coating was chosen for the cell culture experiments, since it has a relatively smooth surface. More than 70% cell viability was observed after 3 days of MTT study. Microwave plasma chemical vapour deposited (MWPCVD) poly-crystalline diamond (PCD) may be one of the promising biomaterial for different bio-medical applications and a very good substitute of the existing implant materials.
Diamond and Related Materials, 2019
Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as... more Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as a reliable alternative to silicon (Si) for high temperature electronics applications, in particular for the electrical vehicles industry. The passivation of SiC devices with diamond films is expected to decrease leakage currents and avoid premature breakdown of the devices, leading to more efficient devices. However, for an efficient passivation the interface between both materials needs to be virtually void free and high quality diamond films are required from the first stages of growth. In order to evaluate the impact of the deposition and seeding parameters in the properties of the deposits, diamond films were deposited on SiC substrates by hot filament chemical vapor deposition (HFCVD). Before the seeding step the substrates were exposed to diamond growth conditions (pre-treatment PT) and seeding was performed with a solution of detonation nanodiamond (DND) particles and with 6-12 and 40-60 m grit. Diamond films were then grown at different temperatures and with different methane concentrations and the deposits were observed in a scanning electron microscope (SEM); their quality was assessed with Raman spectroscopy.
Materials Today: Proceedings, 2018
Generally growth surfaces of polycrystalline microwave plasma enhanced chemical vapor deposited (... more Generally growth surfaces of polycrystalline microwave plasma enhanced chemical vapor deposited (MPCVD) diamond are very rough in nature. So, it is necessary to planarize the surface in order to use them in different industrial applications. High quality polycrystalline diamond (PCD) has been grown by MPCVD process and afterwards the as grown surfaces of these diamonds were polished by mechanical and/or chemo mechanical techniques. The samples were characterized for roughness by non-contact profilometer, quality by Raman spectral analysis and surface morphology by SEM images. It is concluded that mechanical polishing alone can reduce the roughness if correct combination of abrasives are selected.
Diamonds in Scientific Research and High Technology [Working Title], 2019
Characterisations of polycrystalline diamond (PCD) coatings have routinely been done over the pas... more Characterisations of polycrystalline diamond (PCD) coatings have routinely been done over the past three decades of diamond research, but there is less number of reports on some of its very unique properties. For example, diamond is the hardest known material and, in probing such hard surfaces with any indenter tip, it may lead to damage of the instrument. Due to such chances of experimental accidents, researchers have performed very few attempts in evaluating the mechanical properties of PCDs. In the present work, some of these very special properties of diamond that are less reported in the literature are being re-investigated. PCDs were characterised by photoluminescence (PL), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscope (TEM), and X-ray diffraction (XRD) techniques. The diamond surface was also polished to bring the as-grown micron level of surface roughness (detrimental for wear application) down to few hundreds of nanometer. The tribological properties of such polished and smooth surfaces were found to be appropriate for wear protective coating application. This chapter revisits some of the unreported issues in the synthesis and characterisation of PCD coatings grown on Si wafer by the innovative 915 MHz microwave plasma chemical vapour deposition (MPCVD) technique.
Journal of Sol-Gel Science and Technology, 2018
Phase pure, mesoporous, and crystalline V 2 O 5 is synthesized by acid hydrolysis technique and s... more Phase pure, mesoporous, and crystalline V 2 O 5 is synthesized by acid hydrolysis technique and subsequently heat treatment is carried out at 450, 500, 550, and 600°C in air. The as-synthesized and heat-treated powders are thoroughly studied by X-ray diffraction, electron microscopy, dynamic light scattering, and spectroscopic techniques. A unique morphological tuning of V 2 O 5 powders from as small as~80 nm tiny nanorod to as large as a~2.5 μm hexagonal grain as microstructural unit blocks is observed. A qualitative mechanism is suggested for particle growth. Further, the powders are pelletized and subsequently sintered in air at the same temperatures of 450, 500, 550, and 600°C at which the powders were heat treated. Finally, nanomechanical properties of bulk pelletized V 2 O 5 such as nanohardness and Young's modulus are also evaluated by nanoindentation technique at nine different loads e.g.,
Ceramics International, 2019
Solar Energy, 2018
Conducting polymer nanostructures has been recognized as photocatlysts, a promising breakthrough ... more Conducting polymer nanostructures has been recognized as photocatlysts, a promising breakthrough in photocatalysis and other energy conversion application, such as fuel cell and battery in the near future. An efficient light harvesting hybrid nanostructures based on Poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers and gold nanoparticles (Au NPs) was prepared successfully via a one pot colloidal synthetic route. The plasmonic Au NPs (∼6 nm) are synergistically integrated on the conductive polymer nanofibers as evident from microscopic techniques. The Au/Ppy nanohybrids (NHs) demonstrate superior photocatalytic activity for organic pollutant degradation under visible light irradiation which is ∼5.6 times higher than bare polymer (kinetic constant, over 46 times higher than the traditional Au/TiO 2 catalyst). The photoinduced electron transfer from PEDOT nanofibers to Au NPs at the hybrid interface may occurred via a systematic extension of conjugation from polymeric moiety due to the closer proximity of the Au NPs which enhance the charge separation. The high-coverage of Au NPs deposition on the PEDOT nanofibers further allows surface-enhanced Raman scattering to detect the analyte molecules (Dye molecules such as Rhodamine B, Methyl orange) at a concentration of 10 −8 M with an enhancement factor of 10 4. Moreover, Au/PEDOT NHs demonstrated photoelectrochemical activity with the photo current density up to 11.2 mA cm −2 , which is 65% higher than bare PEDOT under similar reaction condition. Hence, Au/PEDOT NHs can be utilize for various applications such as photocatalytic degradation of organic pollutants and as SERS substrate for simultaneous detection of the analyte molecules and water splitting.
Journal of the mechanical behavior of biomedical materials, 2018
Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanopart... more Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanoparticles (CSNPs) of the α-wollastonite phase without using any surfactant or peptizer at the lowest ever reported calcination temperature of 850 °C. Further, the phase purity is confirmed by quantitative phase analysis. The nano-network like microstructure of the CSNPs is characterized by FTIR, Raman, XRD, FESEM, TEM, TGA, DSC etc. techniques to derive the structure property correlations. The performance efficacies of the CSNPs against gram-positive e.g., S. pyogenes and S. aureus (NCIM2127) and gram-negative e.g., E. coli (NCIM2065) bacterial strains are studied. The biocompatibility of the CSNPs is established by using the conventional mouse embryonic osteoblast cell line (MC3T3). In addition, the biofilm inhibition efficacies of two varieties of CSNPs e.g., CSNPs(W) and CSNPs(WC) are investigated. Further, the interconnection between ROS e.g., superoxide (O) and hydroxyl radical (OH) gen...
Ceramics International, 2017
A scalable, cost effective synthesis of reduced graphene oxide (RGO)-magnesium oxide (MgO) hybrid... more A scalable, cost effective synthesis of reduced graphene oxide (RGO)-magnesium oxide (MgO) hybrid nanocomposite (RGOMOHNC) is reported in the present work. The process involves an in-situ sonication method in aqueous medium at room temperature e.g., 30C. The as synthesized graphene oxide (GO) and RGOMOHNC powders are characterized by the XRD, FESEM, TEM, FTIR, RS and XPS techniques. The results indicate that in-situ growth of 20-30 nm MgO nanoparticles effectively increases the graphitic nature of the layered RGO microstructure. The experimentally measured cyclic voltammetry (CV) plots show that the specific capacitance of the RGOMOHNC powders is three orders of magnitude higher than that of the GO powders. A mechanism of RGOMOHNC formation has been proposed.
Plasma Science and Technology, 2017
Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chem... more Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chemical vapor deposition (MPCVD) at different process parameters, and their thermal conductivity (TC) is evaluated by a laser flash technique (LFT) in the temperature range of 230-380 K. The phase purity and quality of the films are assessed by micro-Raman spectroscopy based on the diamond Raman peak width and the amorphous carbon (a-C) presence in the spectra. Decreasing and increasing dependencies for TC with temperature are found for high and low quality samples, respectively. TC, as high as 1950±230 W m −1 K −1 at room temperature, is measured for the most perfect material. A linear correlation between the TC at room temperature and the fraction of the diamond component in the Raman spectrum for the films is established.
Journal of the Mechanical Behavior of Biomedical Materials, 2017
Sustainable Energy & Fuels, 2017
Spherically shaped MOF-derived CeO2@C shows a superior performance as a lithium-ion battery anode... more Spherically shaped MOF-derived CeO2@C shows a superior performance as a lithium-ion battery anode with high specific capacity, rate performance and cycling stability.
Journal of Coating Science and Technology, 2016
Diamond offers a range of unique properties, including wide band of optical transmission, highest... more Diamond offers a range of unique properties, including wide band of optical transmission, highest thermal conductivity, stiffness, wear resistance and superior electronic properties. Such high-end properties are not found in any other material, so theoretically it can be used in many technological applications. But the shortcoming has been the synthesis of the diamond material in the laboratory for any meaningful use. Although microwave plasma chemical vapour deposited (MPCVD) has been in practice since 1980s for the diamond growth but it is in the past 7-8 years that its potential has been realised by the industry due to capability of MPCVD to deposit diamond, pure and fast, for commercial uses. There are many CVD techniques for growing diamond but among them MPCVD can only make single crystal diamond (SCD) effectively. SCD grown by MPCVD is also superior to other forms of diamond produced in the laboratory. For example, SCD is necessary for the best electronic properties-often outperforming the polycrystalline diamond (PCD), the high pressure high temperature (HPHT) diamond and the natural diamond. In many applications the short lateral dimensions of the lab-grown diamond available is a substantial limitation. Polycrystalline CVD diamond layers grown by hot filament CVD solved this problem of large area growth, but the presence of grain boundaries are not appropriate for many uses. On the other hand, there is still limitation in the area over which SCDs are grown by MPCVD, only upto 10-15 mm lateral sizes could have been achieved so far, while there are recipes which rapidly grow several mm thick bulk SCDs. This lateral size limitation of SCDs is primarily because of the small seed substrate dimension. Although natural and HPHT diamonds may not be suitable for the intended application, still they are routinely used as substrates on which SCD is deposited. But the problem lies in the availability of large area natural SCD seeds which are extremely rare and expensive. Moreover, large diamond substrate plates suitable for CVD diamond growth have not been demonstrated by HPHT because of the associated high economic risk in their fabrication and use. Other than lateral dimension, purity of SCD is also very important for technological use. Natural diamond is often strained and defective, and this causes twins and other problems in the CVD overgrowth or fracture during synthesis. In addition, dislocations which are prevalent in the natural diamond substrate are replicated in the CVD layer, also degrading its electronic properties. HPHT synthetic diamond is also limited in size, and generally is of poorer quality in the larger stones, with inclusions being a major problem. There will be much research interest in the next 10 years for the MPCVD growth of SCD. Purer and bigger SCDs will be tried to grow with faster and reproducible MPCVD recipes. Here the MPCVD growth of SCD is being reviewed keeping in mind its huge technological significance in the next decades or so. Discoveries of the commercial productions of silicon, steel, cement different materials have built modern societies but higher scales will be achieved with the advent of lab-grown diamond.
Coatings
In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively follo... more In this work, a diamond/Ti/diamond multilayer structure has been fabricated by successively following thin-film CVD and PVD routes. It has been found that a combined pre-treatment of the silicon base substrate, via argon plasma etching for creating surface roughness and, thereafter, detonation nanodiamond (DND) seeding, helps in the nucleation and growth of well-adherent CVD diamond films with a well-defined Raman signal at 1332 cm−1, showing the crystalline nature of the film. Ti sputtering on such a CVD-grown diamond surface leads to an imprinted bead-like microstructure of the titanium film, generated from the underlying diamond layer. The cross-sectional thickness of the titanium layer can be found to vary by as much as 0.5 µm across the length of the surface, which was caused by a subsequent hydrogen plasma etching process step of the composite film conducted after Ti sputtering. The hydrogen plasma etching of the Ti–diamond composite film was found to be essential for smoothen...
Materials, 2022
Finesse coefficient is one of the most important parameters describing the properties of a resona... more Finesse coefficient is one of the most important parameters describing the properties of a resonant cavity. In this research, a mathematical investigation of the application of diamond structures in a fiber-optic Fabry–Perot measurement head to assess their impact on the finesse coefficient is proposed. We present modeled transmission functions of cavities utilizing a nitrogen-doped diamond, a boron-doped diamond, nanocrystalline diamond sheet and a silver mirror. The diamond structures were deposited using a microwave plasma-assisted chemical vapor deposition system. A SEM investigation of surface morphology was conducted. The modeling took into consideration the fiber-optic Fabry–Perot setup working in a reflective mode, with an external cavity and a light source of 1550 nm. A comparison of the mathematical investigation and experimental results is presented.
Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The... more Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The condition under which the formation of sp3 carbon takes place is a metastable one. There is a requirement of seed material to start the formation of diamond phase, and moreover there are substrates which favour its growth. There is still much scope of research in understanding the metastable synthesis of diamond. Such coatings need to be physically characterised and mechanically polished down to very smooth top surface for any meaningful industrial application. The work plan of the present thesis can be divided into six categories: 1. The nucleation and growth of CVD diamond is first investigated using conventional diamond micron-grit suspension seeding of silicon substrates. 2. Secondly, emphasis was given on the detonation nanodiamond (DND) seeding technique for understanding the metastable growth process of the sp3 phase. It was found that CVD growth conditions lead to capillary rise in pressure inside the vacuum chamber, which thereby replicates high pressure high temperature (HPHT) environment, thus contradicts the prevailing knowledge of metastable diamond synthesis of CVD diamond. 3. Such CVD as-grown diamond films were then characterised using different tools, like XRD, Raman, SEM, XPS etc. 4. Since, 915 MHz microwave frequency was used to grow CVD diamond, it led to coating non-uniformity, over large areas. So, such large area diamond deposition characteristics were then necessary to study. 5. Next, polishing was done on such large area diamond coatings with evaluation of its efficacy. 6. Separately, diamond like nanocomposite (DLN) coating was also deposited by a separate PECVD reactor and characterised for knee implant bio-coating application. In the first chapter of the thesis introductory remarks have been made on the issues involving each of the above six subjects. Second chapter describes the experimental techniques adapted in the thesis work. The third chapter discusses the results obtained from these experiments to address each of the above six sub-categories. The final and fourth chapter concludes the thesis work highlighting the important observations of this PhD study.
Engineering Applications of Diamond, 2021
benefits of the human society [11, 12], like making faster and smaller future electronics, quantu... more benefits of the human society [11, 12], like making faster and smaller future electronics, quantum computers, high power lasers, nuclear energy, capturing carbon for reducing its footprint in the environment [13], medical devices for patients [14] or even water purification [15] for a better standard of living (Table 1). This chapter lists some of the engineering applications where the scientific knowledge of the diamond material property has been used to build/design/create something useful for the people on earth.
Trends in biomaterials & artificial organs, 2015
Diamond is considered as high quality bio-ceramic material due to its physical and mechanical pro... more Diamond is considered as high quality bio-ceramic material due to its physical and mechanical properties. Diamond has the highest hardness as well as it is bio-compatible, non-toxic and chemically inert. Different biological cells growing on the diamond surface indicates that diamond does not interfere in cell growth mechanism. Nucleation side of the freestanding diamond coating was chosen for the cell culture experiments, since it has a relatively smooth surface. More than 70% cell viability was observed after 3 days of MTT study. Microwave plasma chemical vapour deposited (MWPCVD) poly-crystalline diamond (PCD) may be one of the promising biomaterial for different bio-medical applications and a very good substitute of the existing implant materials.
Diamond and Related Materials, 2019
Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as... more Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as a reliable alternative to silicon (Si) for high temperature electronics applications, in particular for the electrical vehicles industry. The passivation of SiC devices with diamond films is expected to decrease leakage currents and avoid premature breakdown of the devices, leading to more efficient devices. However, for an efficient passivation the interface between both materials needs to be virtually void free and high quality diamond films are required from the first stages of growth. In order to evaluate the impact of the deposition and seeding parameters in the properties of the deposits, diamond films were deposited on SiC substrates by hot filament chemical vapor deposition (HFCVD). Before the seeding step the substrates were exposed to diamond growth conditions (pre-treatment PT) and seeding was performed with a solution of detonation nanodiamond (DND) particles and with 6-12 and 40-60 m grit. Diamond films were then grown at different temperatures and with different methane concentrations and the deposits were observed in a scanning electron microscope (SEM); their quality was assessed with Raman spectroscopy.
Materials Today: Proceedings, 2018
Generally growth surfaces of polycrystalline microwave plasma enhanced chemical vapor deposited (... more Generally growth surfaces of polycrystalline microwave plasma enhanced chemical vapor deposited (MPCVD) diamond are very rough in nature. So, it is necessary to planarize the surface in order to use them in different industrial applications. High quality polycrystalline diamond (PCD) has been grown by MPCVD process and afterwards the as grown surfaces of these diamonds were polished by mechanical and/or chemo mechanical techniques. The samples were characterized for roughness by non-contact profilometer, quality by Raman spectral analysis and surface morphology by SEM images. It is concluded that mechanical polishing alone can reduce the roughness if correct combination of abrasives are selected.
Diamonds in Scientific Research and High Technology [Working Title], 2019
Characterisations of polycrystalline diamond (PCD) coatings have routinely been done over the pas... more Characterisations of polycrystalline diamond (PCD) coatings have routinely been done over the past three decades of diamond research, but there is less number of reports on some of its very unique properties. For example, diamond is the hardest known material and, in probing such hard surfaces with any indenter tip, it may lead to damage of the instrument. Due to such chances of experimental accidents, researchers have performed very few attempts in evaluating the mechanical properties of PCDs. In the present work, some of these very special properties of diamond that are less reported in the literature are being re-investigated. PCDs were characterised by photoluminescence (PL), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscope (TEM), and X-ray diffraction (XRD) techniques. The diamond surface was also polished to bring the as-grown micron level of surface roughness (detrimental for wear application) down to few hundreds of nanometer. The tribological properties of such polished and smooth surfaces were found to be appropriate for wear protective coating application. This chapter revisits some of the unreported issues in the synthesis and characterisation of PCD coatings grown on Si wafer by the innovative 915 MHz microwave plasma chemical vapour deposition (MPCVD) technique.
Journal of Sol-Gel Science and Technology, 2018
Phase pure, mesoporous, and crystalline V 2 O 5 is synthesized by acid hydrolysis technique and s... more Phase pure, mesoporous, and crystalline V 2 O 5 is synthesized by acid hydrolysis technique and subsequently heat treatment is carried out at 450, 500, 550, and 600°C in air. The as-synthesized and heat-treated powders are thoroughly studied by X-ray diffraction, electron microscopy, dynamic light scattering, and spectroscopic techniques. A unique morphological tuning of V 2 O 5 powders from as small as~80 nm tiny nanorod to as large as a~2.5 μm hexagonal grain as microstructural unit blocks is observed. A qualitative mechanism is suggested for particle growth. Further, the powders are pelletized and subsequently sintered in air at the same temperatures of 450, 500, 550, and 600°C at which the powders were heat treated. Finally, nanomechanical properties of bulk pelletized V 2 O 5 such as nanohardness and Young's modulus are also evaluated by nanoindentation technique at nine different loads e.g.,
Ceramics International, 2019
Solar Energy, 2018
Conducting polymer nanostructures has been recognized as photocatlysts, a promising breakthrough ... more Conducting polymer nanostructures has been recognized as photocatlysts, a promising breakthrough in photocatalysis and other energy conversion application, such as fuel cell and battery in the near future. An efficient light harvesting hybrid nanostructures based on Poly(3,4-ethylenedioxythiophene) (PEDOT) nanofibers and gold nanoparticles (Au NPs) was prepared successfully via a one pot colloidal synthetic route. The plasmonic Au NPs (∼6 nm) are synergistically integrated on the conductive polymer nanofibers as evident from microscopic techniques. The Au/Ppy nanohybrids (NHs) demonstrate superior photocatalytic activity for organic pollutant degradation under visible light irradiation which is ∼5.6 times higher than bare polymer (kinetic constant, over 46 times higher than the traditional Au/TiO 2 catalyst). The photoinduced electron transfer from PEDOT nanofibers to Au NPs at the hybrid interface may occurred via a systematic extension of conjugation from polymeric moiety due to the closer proximity of the Au NPs which enhance the charge separation. The high-coverage of Au NPs deposition on the PEDOT nanofibers further allows surface-enhanced Raman scattering to detect the analyte molecules (Dye molecules such as Rhodamine B, Methyl orange) at a concentration of 10 −8 M with an enhancement factor of 10 4. Moreover, Au/PEDOT NHs demonstrated photoelectrochemical activity with the photo current density up to 11.2 mA cm −2 , which is 65% higher than bare PEDOT under similar reaction condition. Hence, Au/PEDOT NHs can be utilize for various applications such as photocatalytic degradation of organic pollutants and as SERS substrate for simultaneous detection of the analyte molecules and water splitting.
Journal of the mechanical behavior of biomedical materials, 2018
Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanopart... more Here we report for the very first time the synthesis of 100% phase pure calcium silicate nanoparticles (CSNPs) of the α-wollastonite phase without using any surfactant or peptizer at the lowest ever reported calcination temperature of 850 °C. Further, the phase purity is confirmed by quantitative phase analysis. The nano-network like microstructure of the CSNPs is characterized by FTIR, Raman, XRD, FESEM, TEM, TGA, DSC etc. techniques to derive the structure property correlations. The performance efficacies of the CSNPs against gram-positive e.g., S. pyogenes and S. aureus (NCIM2127) and gram-negative e.g., E. coli (NCIM2065) bacterial strains are studied. The biocompatibility of the CSNPs is established by using the conventional mouse embryonic osteoblast cell line (MC3T3). In addition, the biofilm inhibition efficacies of two varieties of CSNPs e.g., CSNPs(W) and CSNPs(WC) are investigated. Further, the interconnection between ROS e.g., superoxide (O) and hydroxyl radical (OH) gen...
Ceramics International, 2017
A scalable, cost effective synthesis of reduced graphene oxide (RGO)-magnesium oxide (MgO) hybrid... more A scalable, cost effective synthesis of reduced graphene oxide (RGO)-magnesium oxide (MgO) hybrid nanocomposite (RGOMOHNC) is reported in the present work. The process involves an in-situ sonication method in aqueous medium at room temperature e.g., 30C. The as synthesized graphene oxide (GO) and RGOMOHNC powders are characterized by the XRD, FESEM, TEM, FTIR, RS and XPS techniques. The results indicate that in-situ growth of 20-30 nm MgO nanoparticles effectively increases the graphitic nature of the layered RGO microstructure. The experimentally measured cyclic voltammetry (CV) plots show that the specific capacitance of the RGOMOHNC powders is three orders of magnitude higher than that of the GO powders. A mechanism of RGOMOHNC formation has been proposed.
Plasma Science and Technology, 2017
Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chem... more Polycrystalline diamond (PCD) films 100 mm in diameter are grown by 915 MHz microwave plasma chemical vapor deposition (MPCVD) at different process parameters, and their thermal conductivity (TC) is evaluated by a laser flash technique (LFT) in the temperature range of 230-380 K. The phase purity and quality of the films are assessed by micro-Raman spectroscopy based on the diamond Raman peak width and the amorphous carbon (a-C) presence in the spectra. Decreasing and increasing dependencies for TC with temperature are found for high and low quality samples, respectively. TC, as high as 1950±230 W m −1 K −1 at room temperature, is measured for the most perfect material. A linear correlation between the TC at room temperature and the fraction of the diamond component in the Raman spectrum for the films is established.
Journal of the Mechanical Behavior of Biomedical Materials, 2017
Sustainable Energy & Fuels, 2017
Spherically shaped MOF-derived CeO2@C shows a superior performance as a lithium-ion battery anode... more Spherically shaped MOF-derived CeO2@C shows a superior performance as a lithium-ion battery anode with high specific capacity, rate performance and cycling stability.
Journal of Coating Science and Technology, 2016
Diamond offers a range of unique properties, including wide band of optical transmission, highest... more Diamond offers a range of unique properties, including wide band of optical transmission, highest thermal conductivity, stiffness, wear resistance and superior electronic properties. Such high-end properties are not found in any other material, so theoretically it can be used in many technological applications. But the shortcoming has been the synthesis of the diamond material in the laboratory for any meaningful use. Although microwave plasma chemical vapour deposited (MPCVD) has been in practice since 1980s for the diamond growth but it is in the past 7-8 years that its potential has been realised by the industry due to capability of MPCVD to deposit diamond, pure and fast, for commercial uses. There are many CVD techniques for growing diamond but among them MPCVD can only make single crystal diamond (SCD) effectively. SCD grown by MPCVD is also superior to other forms of diamond produced in the laboratory. For example, SCD is necessary for the best electronic properties-often outperforming the polycrystalline diamond (PCD), the high pressure high temperature (HPHT) diamond and the natural diamond. In many applications the short lateral dimensions of the lab-grown diamond available is a substantial limitation. Polycrystalline CVD diamond layers grown by hot filament CVD solved this problem of large area growth, but the presence of grain boundaries are not appropriate for many uses. On the other hand, there is still limitation in the area over which SCDs are grown by MPCVD, only upto 10-15 mm lateral sizes could have been achieved so far, while there are recipes which rapidly grow several mm thick bulk SCDs. This lateral size limitation of SCDs is primarily because of the small seed substrate dimension. Although natural and HPHT diamonds may not be suitable for the intended application, still they are routinely used as substrates on which SCD is deposited. But the problem lies in the availability of large area natural SCD seeds which are extremely rare and expensive. Moreover, large diamond substrate plates suitable for CVD diamond growth have not been demonstrated by HPHT because of the associated high economic risk in their fabrication and use. Other than lateral dimension, purity of SCD is also very important for technological use. Natural diamond is often strained and defective, and this causes twins and other problems in the CVD overgrowth or fracture during synthesis. In addition, dislocations which are prevalent in the natural diamond substrate are replicated in the CVD layer, also degrading its electronic properties. HPHT synthetic diamond is also limited in size, and generally is of poorer quality in the larger stones, with inclusions being a major problem. There will be much research interest in the next 10 years for the MPCVD growth of SCD. Purer and bigger SCDs will be tried to grow with faster and reproducible MPCVD recipes. Here the MPCVD growth of SCD is being reviewed keeping in mind its huge technological significance in the next decades or so. Discoveries of the commercial productions of silicon, steel, cement different materials have built modern societies but higher scales will be achieved with the advent of lab-grown diamond.
MS Thesis, Materials Research Centre, Indian Institute of Science, Bangalore, July, 2003.
Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The... more Chemical vapour deposition (CVD) is used to grow diamond and diamond like carbon (DLC) films. The condition under which the formation of sp3 carbon takes place is a metastable one. There is a requirement of seed material to start the formation of diamond phase, and moreover there are substrates which favour its growth. There is still much scope of research in understanding the metastable synthesis of diamond. Such coatings need to be physically characterised and mechanically polished down to very smooth top surface for any meaningful industrial application. The work plan of the present thesis can be divided into six categories:
1. The nucleation and growth of CVD diamond is first investigated using conventional diamond micron-grit suspension seeding of silicon substrates.
2. Secondly, emphasis was given on the detonation nanodiamond (DND) seeding technique for understanding the metastable growth process of the sp3 phase. It was found that CVD growth conditions lead to capillary rise in pressure inside the vacuum chamber, which thereby replicates high pressure high temperature (HPHT) environment, thus contradicts the prevailing knowledge of metastable diamond synthesis of CVD diamond.
3. Such CVD as-grown diamond films were then characterised using different tools, like XRD, Raman, SEM, XPS etc.
4. Since, 915 MHz microwave frequency was used to grow CVD diamond, it led to coating non-uniformity, over large areas. So, such large area diamond deposition characteristics were then necessary to study.
5. Next, polishing was done on such large area diamond coatings with evaluation of its efficacy.
6. Separately, diamond like nanocomposite (DLN) coating was also deposited by a separate PECVD reactor and characterised for knee implant bio-coating application.
In the first chapter of the thesis introductory remarks have been made on the issues involving each of the above six subjects. Second chapter describes the experimental techniques adapted in the thesis work. The third chapter discusses the results obtained from these experiments to address each of the above six sub-categories. The final and fourth chapter concludes the thesis work highlighting the important observations of this PhD study.