C.R. Kumaran

Bio: C.R. Kumaran is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Diamond & Chemical vapor deposition. The author has an hindex of 7, co-authored 7 publications receiving 130 citations.

Chemical vapor deposition of diamond coatings on tungsten carbide (WC-Co) riveting inserts

Abstract: We report a new industrial application of diamond coatings, by depositing diamond thin films on tungsten carbide (WC–Co) riveting inserts to achieve improved wear resistance and tribological behavior. The riveting inserts are widely used by chain manufacturing industries to guide the pin through its groove. Diamond coatings were deposited on the WC–Co riveting inserts by using hot filament chemical vapor deposition technique. Deposited films were characterized by using X-ray diffraction, a scanning electron microscope (SEM), Raman spectroscopy and a nanoindenter. The SEM micrograph of the deposited films revealed different surface morphologies and crystallite sizes in the groove and in the flat region of the riveting insert. The results concerning the different morphologies and crystallite sizes on the substrate surface are discussed. The coated riveting inserts showed an enhanced performance in the preliminary applied test.

Integration of perovskite PZT thin films on diamond substrate without buffer layer

Abstract: Integration of lead zirconate titanate (PZT) thin film on diamond substrate offers a great deal of potential for the application of multifunctional devices under extreme conditions. However, fabrication of perovskite PZT thin films on diamond substrate without a buffer layer has not been realized to date. We report for the first time on the successful deposition of PZT thin film directly on a diamond substrate without any buffer layer using the pulsed-laser deposition technique. The perovskite phase was realized only under specific growth conditions. X-ray diffraction and Raman studies confirmed the perovskite phase. The ferroelectric behaviour of the deposited PZT thin film was confirmed using piezo response microscope phase image and ferroelectric hysteresis loop.

Growth and characterization of diamond particles, diamond films, and CNT-diamond composite films deposited simultaneously by hot filament CVD

Abstract: It is important to understand the growth of CNT-diamond composite films in order to improve the inter-link between two carbon allotropes, and, in turn, their physical properties for field emission and other applications. Isolated diamond particles, continuous diamond thin films, and thin films of carbon nanotubes (CNTs) having non-uniformly distributed diamond particles (CNT-diamond composite films) were simultaneously grown on unseeded, seeded, and catalyst pre-treated substrates, respectively, using a large-area multi-wafer-scale hot filament chemical vapor deposition. Films were deposited for four different growth durations at a given deposition condition. The changes in surface morphology and growth behavior of diamond particles with growth duration were investigated ex situ using field emission scanning electron microscopy and 2D confocal Raman depth spectral imaging, respectively. A surface morphological transition from faceted microcrystalline nature to nanocrystalline nature was observed as a function of growth duration in the case of isolated diamond particles grown on both unseeded and catalyst pre-treated substrates. However, such a morphological transition was not observed on the simultaneously grown continuous diamond thin films on seeded substrates. 2D confocal Raman depth spectral imaging of diamond particles showed that the local growth of CNTs did not affect the growth behavior of neighboring diamond particles on catalyst pre-treated substrates. These observations emphasize the importance of surface chemical reactions at the growth site in deciding sp2 or sp3 carbon growth and the final grain size of the diamond films.

Zinc oxide as a defect-dominated material in thin films for photovoltaic applications – experimental determination of defect levels, quantification of composition, and construction of band diagram

Abstract: In the present work, thin ZnO layers were synthesized by the sol–gel method with subsequent spin-coating on Si(100). We show that the detailed analysis of lab-recorded photoemission spectra in combination with Kelvin probe data yielded the work function, ionization energy, and valence band – Fermi level separation – and hence enabled the construction of band diagrams of the examined layers. With small modifications in preparation, very different films can be obtained. One set shows a homogeneous depth-dependent n carrier distribution, and another a significant carrier concentration gradient from n-type conductivity to almost metal-like n+ character. Likewise, the surface morphology can be tuned from a uniform, compact surface with spherical single-nm sized grain-like features to a structured surface with 5–10 nm tall crystallites with (002) dominating crystal orientation. Based on the band-bending and the energy levels observed, defects of contradictory nature, i.e. acceptor–donor–trap (ADT) properties, were identified. These defects may be groups of point defects, with opposite character. The ADT states affect the energy levels of the oxide layers and due to their nature cannot be considered in the photoemission experiment as mutually independent. The versatile nature of the synthesis provides us with the opportunity to tune the properties with a high degree of freedom, at low processing costs, yielding layers with an exotic electronic structure. Such layers are interesting candidates for applications in photovoltaic and nanoelectronic devices.