Multi-scale studies on diamond crystal and carbon microtubular growth

Diamond and one-dimensional carbon tubular structures are two of the most technologically important materials today. Electronic devices utilizing the extreme properties of diamond could not be fully realized due to the lack of processes for large single crystals. The traditional methods for producing carbon nanotubes (CNTs) lack the ability to tune the internal diameters and morphologies essential for nano/microfluidics.; In the case of diamond, limited understanding on the origin of defects during homoepitaxy on {lcub}100{rcub} surfaces or during growth on {lcub}100{rcub} facets of individual crystals limits our ability to grow large single crystals (or wafers). In this dissertation, it is hypothesized that the inconsistency in producing defect free diamond layers could be due to the role of gas phase impurities or the initial substrate surface topography. In this dissertation, multi-scale studies comprising zero-dimensional gas phase computations, interrupted growth experiments at different time scales and topographic characterization at different length scales are performed to provide insight into the role of gas phase impurities (such as sulfur) and the role of initial surface topography of diamond substrates on the origin and propagation of defects.; A C-H-O ternary diagram is constructed based on steady state gas phase calculations and the role of sulfur on diamond deposition is studied using this diagram. Based on these studies, it is determined that sulfur increases the compositional window for diamond deposition by altering the gas phase compositions significantly even at concentrations as low as 50 ppm. It is also determined experimentally that sulfur addition affects the quality of diamond crystals by altering the surface chemistry at the growth interface.; Based on the interrupted homoepitaxial growth experiments on diamond {lcub}100{rcub} substrates, the origin of defects have been identified to be the polishing grooves in the <110> direction present on a well polished substrate (<1° off-axis). A macroscopic model based on the 'mis-aligned joining' of two individual homoepitaxial domains over the polishing grooves is presented to explain the occurrence of the spiral growth mode. It is further shown that by removing the sub-surface damage caused by polishing, defect free diamond layers can be grown under the same process conditions.; Studies involving carbon deposition onto liquid metals for diamond films led to the development of a novel growth concept for a new class of carbon tubular morphologies: 'carbon microtubes'. Using a set of multi-scale studies, a macroscopic model for growth is proposed and demonstrated by controlling the morphologies by in-situ tuning of internal diameters and conical angles. In-situ control over carbon tubular growth is achieved by altering the wetting behavior of low-melting metals with carbon by dosing the hydrocarbon feed gases with gas phase impurities such as nitrogen and oxygen.