Synthesis of nanostructured materials
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Controlled synthesis and characterization of vertically aligned carbon nanofibers In the past four years synthesis of vertically aligned carbon nanofibers has become my main area of expertise. Vertically aligned carbon nanofibers are graphitic cylinders that can be synthesized a few tens of microns long with diameters ranging from a few to hundreds of nanometers perpendicular to a substrate. They can be grown deterministically by plasma enhanced chemical vapor deposition (PECVD). Deterministic synthesis means that the nanofiber location and diameter can be defined by deposition of precise amount of catalyst in specified locations and nanofiber composition and structure by precise control of plasma parameters. The length is simply controlled by growth time. While seemingly simple process, PECVD growth of carbon nanofibers is very complex in its nature: at relatively high temperature carbonaceous species catalytically decompose at the surface of a catalyst nanoparticle, resultant carbon dissolves into and diffuses through the catalyst and incorporates into a growing graphitic structure of a fiber. By selecting appropriate temperature, pressure, plasma current and bias, and gas composition precise balance of carbon etching and deposition is achieved on a catalyst surface. Two still not well understood catalytic processes – hydrocarbon decomposition and atomic carbon incorporation of into graphitic nanostructure, and immensely complex plasma chemistry and physics still allows only empirical approach to selection of the appropriate growth conditions to achieve desired properties of the nanofibers. In the past few years, such approach has resulted in understanding some phenomenological relationships and trends that help in a day-to-day production of carbon nanofibers. In the nearest future I am concentrating my efforts on understanding how the internal structure of a carbon nanofiber can be controlled. In particular, I am studying the effects of growth conditions and different catalyst crystal structure and orientation. Special effort has been made to achieve controlled uniform growth of VACNFs on a wafer scale level (e.g. over 100 mm diameter areas). This allows performing standard microfabrication operations using semiconductor processing equipment to produce functional devices. This step is what made nanofibers from being simply interesting materials to actually becoming useful and functional as a part of devices. DC Plasma Enhanced Chemical Vapor Deposition Related publications:
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