Pendeoepitaxy, a form of selective lateral growth of GaN thin films has been developed using GaN/AlN/6H-SiC͑0001͒ substrates and produced by organometallic vapor phase epitaxy. Selective lateral growth is forced to initiate from the (112 0) GaN sidewalls of etched GaN seed forms by incorporating a silicon nitride seed mask and employing the SiC substrate as a pseudomask. Coalescence over and between the seed forms was achieved. Transmission electron microscopy revealed that all vertically threading defects stemming from the GaN/AlN and AlN/SiC interfaces are contained within the seed forms and a substantial reduction in the dislocation density of the laterally grown GaN. Atomic force microscopy analysis of the (112 0) face of discrete pendeoepitaxial structures revealed a root mean square roughness of 0.98 Å. The pendeoepitaxial layer photoluminescence band edge emission peak was observed to be 3.454 eV and is blueshifted by 12 meV as compared to the GaN seed layer.

By controlling the angular relation of the substrate surface with respect to the incoming vapor direction in an evaporation deposition system, it is possible to engineer the morphology of thin films. Sculptured nematic thin films result under low adatom mobility conditions when the substrates are rotated about an axis perpendicular to the vapor direction. Thin films of MgF2 were deposited onto room temperature substrates to produce columnar morphologies ranging from chevron structures to continuously varied structures resembling S shapes and C shapes. The specific morphologies are virtually unlimited within the restriction that the minimum angle χM of the local columnar direction with respect to the substrate plane is about 30°.

A new process route for lateral growth of nearly defect free GaN structures via Pendeoepitaxy is discussed. Lateral growth of GaN films suspended from {112 − 0} side walls of [0001] oriented GaN columns into and over adjacent etched wells has been achieved via MOVPE technique without the use of, or contact with, a supporting mask or substrate. Pendeo-epitaxy is proposed as the descriptive term for this growth technique. Selective growth was achieved using process parameters that promote lateral growth of the {11 2 − 0} planes of GaN and disallow nucleation of this phase on the exposed SiC substrate. Thus, the selectivity is provided by tailoring the shape of the underlying GaN layer itself consisting of a sequence of alternating trenches and columns, instead of selective growth through openings in SiO 2 or SiN x mask, as in the conventional lateral epitaxial overgrowth (LEO).Two modes of initiation of the pendeo-epitaxial GaN growth via MOVPE were observed:Mode A -promoting the lateral growth of the {112 − 0} side facets into the wells faster than the vertical growth of the (0001) top facets; and Mode B -enabling the top (0001) faces to grow initially faster followed by the pendeo-epitaxial growth over the wells from the newly formed {112 − 0} side facets. Four-to-five order decrease in the dislocation density was observed via transmission electron microscopy (TEM) in the pendeo-epitaxial GaN relative to that in the GaN columns. TEM observations revealed that in pendeo-epitaxial GaN films the dislocations do not propagate laterally from the GaN columns when the structure grows laterally from the sidewalls into and over the trenches. Scanning electron microscopy (SEM) studies revealed that the coalesced regions are either defect-free or sometimes exhibit voids. Above these voids the PEGaN layer is usually defect free.

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Before its uptake and oxidation by purple sulfur bacteria, elemental sulfur probably first has to be mobilized. To obtain more insight into this mobilization process in the phototrophic purple sulfur bacterium Allochromatium vinosum, we used HPLC analysis and X-ray absorption near-edge structure (XANES) spectroscopy for the detection and identification of sulfur compounds in culture supernatants and bacterial cells. We intended to identify soluble sulfur compounds that specifically occur during growth on elemental sulfur, and therefore compared spectra of cultures grown on sulfur with those of cultures grown on sulfide or thiosulfate. While various unexpected oxidized organic sulfur species (sulfones, C–SO2–C, and sulfonates, ) were observed via XANES spectroscopy in the supernatants, we obtained evidence for the presence of monosulfane sulfonic acids inside the bacterial cells by HPLC analysis. The concentrations of the latter compounds showed a tight correlation with the content of intracellular sulfur, reaching their maximum when sulfur began to be oxidized. None of the detected sulfur compounds appeared to be a specific soluble intermediate or product of elemental sulfur mobilization. It therefore seems unlikely that mobilization of elemental sulfur by purple sulfur bacteria involves excretion of soluble sulfur-containing substances that would be able to act on substrate distant from the cells.