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An anomalous lineshape of stimulated Raman spectra obtained from the region very close to the nozzle of supersonic pulsed expansions of nitrogen is presented. High-resolution Raman spectra of the Q branch of the fundamental vibration mode of N2 have been recorded from two different nitrogen expansions at T0 = 295 K and P0 = 1.5-3.5 bar, the lasers crossing the jet axis in the range z/D = 0.25-1.25, where D is the effective nozzle diameter. The combination of Doppler shifts and strong gradients of density and temperature in the near-nozzle region yield an inhomogeneous broadening and a double peak structure of the recorded Raman line profiles. The comparison of the experimental results with the simulation of the Raman spectrum from this region provides valuable information about the near-nozzle flow field. The lineshape described here is different from another reported previously in the literature, which is based on a depletion of the density of free molecules on the axis due to condensation.

The kinematic conditions under which III-Nitrides films can be grown were determined using efficient local-orbital molecular-dynamics simulations. Reaction paths for the impact of ammonia molecules on the cation- and anion-terminated surfaces of GaN and AlN were also determined. In situ growth experiments of GaN on 6H-SiC(0001) substrates were conducted in the low-energy electron microscope (LEEM). Initial nucleation at the steps and subsequent growth across the terraces were observed. The LEED patterns indicated three-dimensional crystal growth with pronounced formation of facets. Such growth behavior occurred irrespective of the method of deposition. A seeded beam source chamber has been interfaced with a UHV deposition chamber. Films of A1N have been grown with this system. Smooth, homoepitaxial GaN films were grown using an effusive Ga source and an NH3-seeded supersonic molecular beam. A small Ga flux-substrate temperature window was found that allows for two-dimensional homoepitaxial growth under MBE-like conditions (TS=730 deg C, pb-2x10(exp -6) Torr). Mass-analyzed Ga(+),N2(+) and N(+) ions at approx. 20 eV with a small energy spread of tilde 1 eV at FWHM were produced via two Colutron units with deceleration lenses. Ion beams of N2(+) and N(+) were used to perform nitridation of Si(100) surfaces. Subsequent SIMS depth profiles indicated the presence of nitride layers on the Si(100) substrates. Codeposition of Ga and N on Si(111) and Si(100) substrates was conducted with the Ga(+) and N2(+) ion beams. SIMS depth profiles showed the presence of both Ga and N on the Si substrate surfaces suggesting the formation of a GaN layer. A second generation arc-heated jet source and an inexpensive corona discharge source were designed, fabricated and characterized. Preliminary optical spectra of theses sources were obtained and evaluated. An improved optical and elec

The initial phase of research to develop a Monte Carlo description of the flow within an ionic sampling mass spectrometer. Procedures for handling multiple species, chemical reactions and internal energy transfer are discussed at length. The flow through a sonic orifice for major species is computed and methods for handling minor species are presented. (Author)