Ph.D. / Applied Physics / Spectral analysis of field emission noise induced by emitter surface equilibrium density fluctuations is developed. The noise spectrum factors as S (ω) = S (ω) + SB (ω) for a canonical ensemble, which characterizes adsorbate covered emitters. S∞ (ω) and SB (ω) correspond to unbounded diffusion and the boundary effect respectively. Chemical diffusivity D [subscript c] is defined by Fick's first law. Its equilibrium limit, termed hydrodynamic D [subscript h], is derived from S (ω) and related to the adsorbate fluctuations. These diffusivities are compared using irreversible thermodynamic and Kubo relations. Their equality is ensured by evaluation of the excess entropy production only when the density gradient is small and no phase change occurs. Two dimensional adsorbate phase transitions are identified by correlating incipient nonlinearity in the Arrhenius plot of diffusivity with the onset of a temperature dependent total noise power, which is proportional to adsorbate isothermal compressibility. Examples using K/W, Xe/W, and H/W are given. Thermal field emission noise is characterized by a grand canonical ensemble (GCE). Here the diffusive fluctuation mechanism includes adatom creation and defect vacancy formation resulting from surface free energy minimization. Adatom dynamics are governed by a stochastic diffusion equation. A multidimensional version of Carson's theorem is formulated, which leads to S(ω) ≈ C( x =0, ω) N[subscript c][superscript -1](ω), where (hkl) geometry affects C( x =0, ω) and N[subscript c](ω) accounts for probe spatial averaging. From this factorization of S (ω) an outstanding noise power divergence problem for diffusive equilibrium fluctuations within a GCE is solved. The solution requires finite fluctuation lifetime, which is also proved to be a necessary equilibrium condition. The other part of the solution leads to a new method of measuring the resolution of the microscope. Derived values agree well with a calculation that considers the transverse momentum distribution of the field emitted electrons. The S (ω) characteristics of tungsten thermal field emission from W (112), W (310), and W (100) planes are explained in detail. Diffusivity values, their corresponding activation energies, and the defect vacancy formation activation energy agree well with other experimental data. Conditions for the broadest band S (ω) [proportional] ω [superscript -1] are given and a hypothesis is proposed explaining its frequent occurrence for diffusive equilibrium systems.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Oregon Graduate Center, 1985.

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An experimental search based on previous published theoretical work was made for de Haas-van Alphen-like quantum oscillations in field emission current. The study was motivated by the possible applicability of de Haas-van Alphen measurements to the study of Fermi surfaces near real surfaces, Field emitters were fabricated from bismuth single crystals grown from the melt by a modified Bridgeman technique. Field emission current was measured with the field emitter cooled by contact with a liquid helium bath. Most measurements were made at 4.2° K, although a few measurements were made at 2.02°K; Fowler-Nordheim plots of the experimental current-voltage data were linear over several orders of magnitude. The field emission current was measured as a function of magnetic field strength to twenty kilogauss and as a function of direction, with respect to the emitter axis, for a steady field of ten kilogauss. The results of measurements on four field emitter crystals are reported in this thesis. In most of this work, de Haas-van Alphen-like quantum oscillations were not observed. In one set of data, however, de Haas-van Alphen-like oscillations having a period of 0.50 x 10⁻⁵ G⁻¹ appear to be present. The published theoretical work was reevaluated. As a result of a large effective Dingle temperature for field emitters, and because the effective masses of carriers in bismuth are anisotropic, the de Haas-van Alphen effect in field emission current could be several times smaller than has been suggested in the literature. The sensitivity of the experiments reported in this thesis was not sufficient to allow unambiguous identification of quantum oscillations at the reduced level. An outline of an experimental procedure suitable for observation of the de Haas-van Alphen-like effect in field emission current at the reduced level is provided in the final chapter.

Using the vapor-liquid-solid (VLS) growth method, silicon nanowires and germanium nanowires are grown. We find the high growth rate is responsible for the silicon nanowires with less growth defects when they are grown by use of silicon tetrachloride as a precursor and hydrogen as a carrier gas. Based on this funding, large area, high aspect ratio, h111i oriented silicon nanowires are successfully grown on Si (111) and Si (100). Novel growth mechanisms of VLS growth method were discovered in SiOx nanoflowers and silicon nanocones. In SiOx nanoflowers grown at the tip of silicon nanowires, it is found that they are produced via the enhanced oxidation of silicon at the gold-silicon interface. Furthermore, the analysis of the flower pattern reveals that it is the observation of the dense branching morphology on nanoscale and on spherical geometry. For the silicon nanocones, they are grown by the in situ etching of the catalysts of Ga/Al by HCl during the growth. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) reveal that the nanocones are composed of amorphous silicon oxides and crystalline Si. Based on the similar chemistry of hydrogen reduction of SiCl₄ for the growth of silicon nanowires, single crystalline germanium nanowires are grown by use of GeCl4 as a precursor and H₂ as a carrier gas. As one of important application of one dimensional nanostructures, the field emission properties of 1-D nanostructures are explored. The field emission properties of a single graphite nanocone are measured in SEM. The inter-electrode separation is controlled using scanning tunneling microscopy (STM) approach method, allowing the precise and ne determination of the separation. Its Fowler-Nordheim plot shows it emits currents in accordance with the Fowler-Nordheim field emission. Its onset voltage, field enhancement factor show that its basic field emission parameters are comparable to those of a single carbon nanotube. It is observed that single nanocone is damaged after emitting a current of about 100 nA, which seems to be due to its hollow interior structure. / text

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