A new technique has been developed for producing mono-crystalline foils of some alkali halides for transmission electron microscopy. The formation mechanism of the crystals has been investigated. The foils, which have two free faces have been used as electron transparent substrates to grow epitaxial films of gold, on one or both surfaces of the substrates. It has been shown that by covering the above foils with a thin layer of another alkali halide, bending contours suitable for measuring the thickness of the foils, are produced. A chamber has been designed and constructed for transporting the specimen from the preparation vacuum system into the electron microscope without exposing it to the atmosphere. The variation of pressure inside the chamber has been measured and some possible modifications have been suggested. The device has been used to study the nucleation and growth from the vapour phase of LiF, NaF, NaCl, KOI, KBj, KI and Rbl, on electron transparent substrates of mica and potassium chloride. The crystallographic and atomic orientations of the above materials with respect to atomic arrangement of the substrates have been studied. It has been shown that the alkali halides form continuous films at average thicknesses below 2.5 nm on substrates of mica and KCl. The effect of the heat treatment during and after growth of the films has been studied. The effects of atmospheric moisture on the overgrowths have been studied in detail, and it has been shown that there are some similarities between the effects of atmospheric moisture and the heat treatment on the hygroscopic alkali halides. It has been shown that when thin deposits of NaCl on the substrate of KCl are heated, diffusion or re-evaporation of the deposit does not occur randomly. The consequent possibility of the existence of periodic defect sites has been discussed. From a general consideration of the results it is concluded that (a) Chemical interactions are a dominant factor in the epitaxial growth of alkali halides on mica and KCl. (b) The alkali halides deposited from vapour consist of flat crystallites at the earliest stages of growth at room temperature.

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<p> In this dissertation, the nature of magnetism in transition-metal-doped phthalocyanines (TMPc, TM = Co, Ni, Cu, V, and Mn, chemical formula: C₃₂H₁₆N₈TM) is investigated by measuring their magnetization (M) and ac susceptibilities in magnetic fields up to 90 kOe and covering the wide temperature range of 0.5 K to 300 K. These low temperatures and high magnetic field measurements combined with detailed analysis of the data have provided new information about the nature of magnetism of TMPc. The powder samples used here were structurally characterized using x-ray diffraction and scanning electron microscopy.</p><p> TMPc are a class of organic semiconductors with potential applications in spintronics and they are planar molecules with the TM atom at the center bound to four N atoms and forming a linear chain along the monoclinic b-axis. Because of this symmetry, the ground states of TMPc often violate the Hunds&rsquo; rules; e.g. the S = 3/2 state for d⁵ Mn(II) in &beta;-MnPc, S = 1/2 state for the d⁷ Co(II) in &beta;-CoPc, and S = 0 state for the d⁸ Ni(II) in NiPc. The magnetic properties of TMPc are also affected by the stack angle &delta; between the orientation of the molecular plane and the b-axis, &delta; being 65&deg; (45&deg;) for &alpha; (&beta;) phase. </p><p> For both &alpha;-CuPc and &beta;-CuPc, M vs. T data fit well with the Bonner-Fisher model for S = 1/2 antiferromagnetic (AFM) Heisenberg linear chain yielding the Cu²⁺-Cu²⁺ exchange constant J_ex/k_B = - 1.7 K (- 0.2 K) for &alpha;-CuPc(&beta;-CuPc). This order of magnitude difference in J_ex/k_B is likely due to the smaller Cu²⁺-Cu²⁺ distance in &alpha;-phase than in &beta;-phase. The M vs. H at 2 K and 5 K data are interpreted including the effect of the exchange coupling. </p><p> For &beta;-CoPc, the predicted peak in &chi; vs. T data by Bonner-Fisher model was observed at T_max = 1.9 K for the first time yielding the Heisenberg exchange constant J_ex/k_B = - 1.5 K between the Co²⁺-Co²⁺ ions. The isothermal data of M vs. H at 1 K shows good agreement with the Bonner-Fisher model; M vs. H at 5 K data is interpreted by including the effect of the exchange interaction. </p><p> For VOPc (phase II), the analysis of the M vs. T data shows VO²⁺ electronic state with spin S = 1/2 and &thetas; = - 0.1 indicates a very weak AFM exchange coupling between neighboring VO²⁺ ions which implies the near-perfect paramagnetism of VOPc. This conclusion is also supported by the analysis of the M vs. H data at several temperatures. The diamagnetic nature of &beta;-NiPc corresponding to the S = 0 state for the 3d⁸ Ni(II) is confirmed by measurements and analysis of the magnetization with temperature-independent susceptibility &chi;_D = - 3.38 &times; 10^-7 emu/gOe. The observed ferromagnetic component in the &beta;-NiPc powder sample is identified with Fe impurity. </p><p> For &beta;-MnPc with S = 3/2, detailed analysis of the dc and ac susceptibilities leads to the conclusion of the absence of 3-dimensional long range magnetic ordering in this system contrary to previous reports. This conclusion is supported by the Arrott plots and lack of a peak in the ac susceptibilities and specific heat near the quoted T_C &ap; 8.6 K. Instead, &beta;-MnPc is best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J_ex/k_B = 2.6 K and the single ion anisotropy energy constant |D|/kB = 8.3 K. The absence of 3D long-range ordering is consistent with the measured |D| being >J_ex.</p>

Single crystals of l-ascorbic acid and partially deuterated l-ascorbic acid were irradiated in the temperature range of 77K to 300K by either x-rays from a 3 Mev Van de Graaff electron accelerator or UV radiation (337.1 nm) from a pulsed nitrogen gas laser having a peak power of 240 KW. Several types of free radicals were produced by the radiation and were studied by X-band and Q-band ESR from 4.2K to 300K. The kinds of radicals produced by the UV and x-irradiation were the same. The relative intensities of the spectral lines of the different types of radicals depend upon both the temperature and the type of radiation. Four radicals were identified: two oxidation products (radicals I and IV), one neutralized anion (radical III), and one adduct (radical II). Radicals I, III, and IV are present at 77K after irradiation at 77K. Upon annealing to 140K, radical I changes to dehydroascorbic acid and proton adduction creates radical II. Upon annealing to 300K, radicals II, III, and IV remain and are stable at 300K for at least several months. All four radicals are carbon based radicals and are located on the furan ring. All hyperfine couplings are to (beta)-protons. No carbon-13 hyperfine couplings were observed. ENDOR was tried at 4.2K, 77K, and 300K after x-irradiation at 77K or 300K. In all cases a matrix ENDOR line was observed, but no hyperfine ENDOR lines were observed. UV bleaching was attempted at 300K on a deuterated crystal which had been x-irradiated previously. The UV laser radiation had no observable effect on the ESR spectra in which radicals II, III, and IV were already present. / Source: Dissertation Abstracts International, Volume: 41-10, Section: B, page: 3822. / Thesis (Ph.D.)--The Florida State University, 1980.

Energy studies of the constituents of a mass-selected Gallium Liquid Metal Ion Source (LMIS) are presented. Results were obtained showing double energy loss peaks for Ga$\sbsp{2}{+},$ Ga$\sbsp{3}{+},$ and Ga$\sbsp{4}{+}$ which have not previously been reported in the literature. These loss peaks coincided with higher LMIS emission current, and some of the heavier mass peaks in the LMIS mass spectrum were observed to simultaneously diminish. The relationship of these two observations is discussed in terms of classical liquid drop fission theory. This theory predicts classical fissioning barriers and gives a range of possible parents. The fissioning times of various assumed parents for the given daughters is calculated and inferences concerning the manner of fissioning--asymmetric or symmetric--and their viability are presented. The apparatus used to perform the experiment and its implementation is discussed. / Source: Dissertation Abstracts International, Volume: 55-08, Section: B, page: 3383. / Major Professor: David M. Lind. / Thesis (Ph.D.)--The Florida State University, 1994.

Experimental results concerning the multiphonon scattering of He from the LiF(001) surface, the structure of the NiO(001) surface probed by $\sp3$He scattering, and the structure and dynamics of the CoO(001) surface are presented. Experiments measuring the multiphonon background of He scattered from the LiF surface were used to model the form factor of the interaction for the atom-surface system. This modeling yielded a surface Debye frequency of $\omega\sb{D} = 6.8\times10\sp{13}$ rad/s, the stiffness parameter in the Mott-Jackson matrix element $\beta\ =\ 9.5\ {\rm\A}\sp{-1}$, and a parallel "cutoff" factor $Q\sb{c}\ =\ 8.5\ {\rm\A}\sp{-1}$ for this system. Experiments to determine the structure of NiO using $\sp3$He as the incident probe atom were performed to search for an interaction between the antiferromagnetic ordering in the NiO surface and the nuclear spin in the $\sp3$He. These experiments showed no evidence of any magnetic scattering. It was shown that the mixing of $\sp3$He and $\sp4$He can be used to produce $\sp3$He beams with velocity distributions unobtainable from pure $\sp3$He. Experiments scattering He from the surface of a single crystal CoO sample were used to estimate the peak-to-peak corrugation of CoO for He with an incident wave vector of 6.7 A$\sp{-1}$ at 0.19 A. In addition, the Rayleigh phonon surface dispersion was measured over approximately half of the Brillouin zone. / Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3953. / Major Professor: James G. Skofronick. / Thesis (Ph.D.)--The Florida State University, 1994.

High resolution helium atom scattering (HAS) experiments were performed on the disordered surface of KCN(001) in the rhombohedral phase and on expitaxial grown layers of KBr on RbCl(001). The experiments on KCN used the time-of-flight (TOF) method to measure multiphonon interactions of the incident helium atoms with the crystal surface as a function of incident energy and crystal temperature. These measurements were used to model a cutoff factor ($Q\sb{c} = 4.5{\rm\A}\sp{-1}$) for parallel momentum transfer, a range parameter ($\beta$ = 4.5A$\sp{-1}$) of an exponential potential $V\propto$ exp(-$\beta z$), and a surface Debye temperature ($\Theta\sb{S}$ = 195K). / The experiments with RbCl involved the deposition of one to three monolayers of KBr onto the RbCl(001) surface, which was monitored in situ by attenuation of the atomic helium beam. Inelastic scattering experiments were performed on each atomic layer to determine the surface phonon dispersion curves as a function of coverage. This experiment was performed to validate and also, to provide additional results that will extend the shell model for ionic insulators. Measurements were made in both the ${\overline{\Gamma M}}$ and ${\overline{\Gamma X}}$ high symmetry directions for coverages of one, two, and three monolayers. The KBr/RbCl system which is nearly perfectly lattice matched is compared to the KBr/NaCl system which has lattice registry of 6 KBr to 7 NaCl. / Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3955. / Major Professor: J. G. Skofronick. / Thesis (Ph.D.)--The Florida State University, 1994.

The two-dimensional antiferromagnetic Heisenberg model and $t - J$ model are studied on the square lattice aimed to understand certain normal state properties of the high-temperature copper-oxide superconductors. Fundamental physical issues such as the role of quantum spin fluctuations, and hole dynamics are addressed. We constructed a variational wave function for the Heisenberg model, which includes spin-spin correlations and possesses antiferromagnetic long range order. Long and short wave length spin excitations are calculated using this wave function and compared with neutron scattering and Raman scattering experiments. Loop-expansions up to two-loop level are applied to study the spectral function of a single hole described by the $t - J$ model. Our numerical solutions extrapolated to the thermodynamical limit show that the hole spectral function consists of a sharp lowest-energy quasihole peak and a series of well defined peaks above it, which correspond to the "string" excitations. The single hole spectral weight of the t-J model is also calculated using the Green's function Monte Carlo method to further clarify the controversial question of whether or not the Fermi liquid theory breaks down in this model due to a vanishing spectral weight. / Source: Dissertation Abstracts International, Volume: 54-03, Section: B, page: 1473. / Major Professor: Efstratios Manousakis. / Thesis (Ph.D.)--The Florida State University, 1993.

The penetration of a quasistatic electric field into an epitaxial film of Yba$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ was studied around the film's transition temperature. The electric field penetration into the YBa$\sb2$Cu$\sb3$O$\sb{\rm 7-x}$ electrode was shown to vary by as much as 100A in the temperature regime 60K $<$ T $<$ 110K. The distance between the physical interface and the effective electrical interface is at least 100A at temperatures within 25K of T$\sb{\rm c}$. The direction of interfacial movement is reversed at T$\sb{\rm c}$. The data are consistent with the continuous movement, with changing temperature, of an interface between two regions, one penetrated by the electric field and one devoid of electric field. / The data indicate far stronger temperature dependance and magnitude of the delocalization forces along the c-axis of the material in both the superconducting and normal state than could be expected from any conventional theory of metals. / Applying a dc bias to the films, the effect of charge carrier concentration on T$\sb{\rm c}$ was studied. The first and second derivatives of T$\sb{\rm c}$ with respect to surface carrier concentration were determined to be, respectively, near zero and negative. / Source: Dissertation Abstracts International, Volume: 54-03, Section: B, page: 1471. / Major Professor: Louis R. Testardi. / Thesis (Ph.D.)--The Florida State University, 1993.