Nanomechanics of one-dimensional nanostructures

Silicon carbide nanowires were synthesized via the vapor-liquid-solid (VLS) mechanism by plasma enhanced chemical vapor deposition using orthocarborane (C2B10H12) as the molecular precursor. Nickel boride was the catalyst used to initiate VLS growth, however, high resolution transmission electron microscopy and selected area diffraction revealed that the catalyst transformed to nickel silicide. The source of silicon was determined to be the substrate. The orthocarborane partial pressure dictated whether the catalyst transformed from nickel boride to nickel silicide. In the event that the catalyst did not transform to nickel silicide, boron carbide nanowires were grown instead of silicon carbide. The factors affecting the transformation of the catalyst are the concentrations of B and Si in the vapor and the chemical potentials of the liquid phases of nickel boride and nickel silicide. A temperature gradient within the catalyst is proposed to explain the formation of the frequently observed bi-phase amorphous/crystalline silicon carbide nanowires.; Silica nanowires were synthesized also via the VLS mechanism by chemical vapor deposition using a mixture of silicon and silicon oxide as the precursor. Deposited Iron particles on a silicon substrate served as the catalyst of the growth. Scanning electron microscopy analysis showed the nanowires grew up to tens of microns with diameters ranging from 50 to 200 nm. Selected area diffraction in the transmission electron microscopy verified the amorphous structure of the nanowires. Moreover, energy dispersive spectroscopy and x-ray and XPS analysis suggest that the as-grown nanowires are SiO2.; Nanowires could be potentially useful in designing nanomechanical systems which lead to the interest in understanding their mechanical properties. In this dissertation, the technique of digital pulse force microscopy (DPFM) has been used to analyze the mechanical properties of suspended SiC nanowires. The SiC nanowires were suspended on a silicon grating with trenches of 1.5 micron width and 1 micron height. The silicon grating was coated with a thin thermo-polymer layer to adhere the nanowires to the substrate. Deflection measurements and hence calibrated force-distance curves along the length of the nanowire were obtained. The resultant curves were fitted to various classical beam deflection models to understand the behavior of the nanowire during the deflection measurement and then to compute the elastic modulus for the nanowire. The measurement was conducted on nanowires with different diameters and suspended lengths. The average elastic modulus for the SiC nanowires in this experiment was 71 GPa for the simple support model. Detailed analysis of deflection measurements demonstrates the danger of depending on midpoint bending measurements which give the DPFM superiority over typical force-distance measurement in AFM contact mode. This technique also minimizes the lateral force applied to the nanowires during the typical contact mode.