The microscopic structure and dynamics of cytoplasmic water in the cells of organs and tissues are not well-understood. Much work has been done using various experimental techniques to study the properties of water in living systems, yet there is no generally accepted model describing the interaction of water with cellular constituents. Quasi-elastic neutron scattering (QNS) is a technique capable of a spatial resolution of 1-10 (ANGSTROM) and a frequency resolution of 10('9) to 10('13) sec('-1) which is suitable for the study of the diffusive motion of water in biological systems. A monochromatic beam of 0.95 THz neutrons was used to obtain QNS spectra within an energy window of (+OR-)0.2 THz for momentum transfer values in the ranges of 0.5 (ANGSTROM)('-1) to 1.9 (ANGSTROM)('-1). We have obtained QNS spectra for water in sartorius and gracilis major muscles of green leopard frogs (Rana pipiens pipiens) at 30(DEGREES)C and comparison spectra for a .15 molar solution of KCl at 3(DEGREES)C. The spectra were interpreted with a jump-diffusion model for translational water motion in both systems and a bound-free model for water in the muscle. The measured diffusion parameters of these two systems indicate that the water motion is more restricted in the frog muscle than in the aqueous KCl solution. We estimate the bound fraction of water in muscle to be 15.0 (+OR-) 4.1%. Our results for the bound water fraction in muscle and diffusion coefficients and correlation times of water in muscle and in a .15 m KCl solution agree well with the QNS and NMR results of others.

Metastable Atom De-excitation Spectroscopy (MDS) provides a powerful technique with which to investigate surface electronic structure with unparalleled surface specificity. In this technique a thermal energy beam of noble-gas metastable atoms is directed at the surface under study and the kinetic energy distribution of ejected electrons that result from metastable atom de-excitation is measured. Although the measured distribution contains information about the electronic structure of the outermost surface layer, its detailed analysis requires knowledge of the dynamics of the metastable atom-surface interaction. In the present work, these dynamics have been investigated directly, for the first time, by use of spin-labeling techniques. The electron spins on the incident metastable atoms are polarized and the spin-polarization of the ejected electrons is measured with a Mott polarimeter. Results are reported for Cu(100) and Ni(111) surfaces under a variety of surface conditions. The data indicate that metastable atom-surface interactions may be more complex than is generally assumed and thus suggest that assumptions inherent in earlier analyses of MDS spectra merit additional investigation. The present work further demonstrates the power of spin-resolved measurements in the study of particle-surface interactions and in surface spectroscopies in general.

There is a possibility that an isomer can be found which could be used to obtain a sufficient population inversion density to bring about nuclear lasing. If it can be realized, a gamma ray laser ("graser") will be a new source of radiation in the $\sim$ 1A region of unexcelled spectral brightness and coherence, and can be expected to have revolutionary consequences for physics, biology, and chemistry. The result of our research is that the effects of crystallinity are of crucial importance in considerations regarding gamma-ray lasers, bringing in new elements to laser theory which could very well prove decisive in determining whether grasing can or cannot be achieved. Certain multi-beam Borrmann eigenmodes of the radiation field in a perfect crystal have much stronger coupling to the emitting nuclei, and much less photoabsorption, than modes in the amorphous case. These modes may be selectively fed by nuclear transitions of the proper multipolarity. A crystal containing such emitters would require orders of magnitude less population inversion density in order to lase than would an amorphous sample of similar material. Multi-beam Borrmann modes also have several applications to single-photon optics, particularly the problem of anomalous emission of a $\gamma$-ray by an internal source of multipolarity M1 or higher. While this effect can occur for a 2-beam Borrmann mode, even stronger anomalous emission is possible into multi-beam Borrmann modes. In addition, certain multi-beam Borrmann modes can anomalously transmit resonant radiation through a Mossbauer crystal. (This cannot occur for the 2-beam modes, except for the case of an E1 transition, since the Borrmann mode couples strongly to the nuclei and thus will be strongly absorbed at resonance.)

Presented here are experimental/theoretical studies of the geometric structure of a Cu(001) surface and the near-surface layer magnetization of a ferromagnetic Ni(111) surface, both using spin-polarized low energy electron diffraction (SPLEED). This probe shows great promise both as a high quality structural probe, and also in a variety of magnetic studies. Significant advances have been made over the past several years in both experimental and calculational LEED techniques. The introduction r-factor analysis and streamlining of calculational codes now allows the evaluation of increasingly complex structures by LEED I-V analysis. In addition, experimental advances now allow the investigation of not only the intensities, but also the spin-dependence of scattering from many surfaces. Spin dependence in low-energy electron diffraction is found for scattering from all surfaces, and is due to two effects--the spin-orbit interaction and the exchange interaction. The former is sensitive to the positioning of ions that make up the surface and provides complementary probe of surface geometric structure in addition to LEED intensity analysis. Here we introduce a simple r-factor analysis to evaluate the structure of Cu(001). This surface was chosen because it is well studied, and a highly precise structural determination of the surface based on LEED I-V analysis is available for comparison. Experimental SPLEED A-V profiles are compared with calculated profiles to obtain the best near-surface structure. In this study, the comparison between calculated and experimental spin-asymmetry profiles obtained from this surface is unusually good, and further, the best fit is for a structure that agrees well with the previous LEED study. The present study is the first use of r-factor in a SPLEED structural determinations. Several things are readily noted from the present SPLEED r-factor analysis. First the precision of structural conclusions obtainable r-factors is much greater than possible using the visual inspection method found elsewhere. Further, because A-V's are self-normalizing, the r-factors are cleaner, requiring no arbitrary scaling factor. Also the spin asymmetries show more sensitivity to structural variations than do the comparable LEED intensities. The exchange interaction is sensitive to the electron spin-population density in the surface, an thus to surface magnetism. Our preliminary study of the ferromagnetic Ni(111) surface shows very small exchange asymmetry effects. The results are consistent with some enhancement of the sample magnetization at the surface, but a precise layer magnetization determination is beyond the limits of present technique.

Cold semiconductor clusters of Si, Ge, and GaAs have been produced by laser vaporization followed by supersonic expansion in a helium carrier. The neutral clusters were characterized by F$\sb 2$ (7.89 eV) and ArF (6.4 eV) excimer laser ionization accompanied by time-of-flight mass analysis. A semiconductor cluster ion apparatus has been developed for characterizing ionic cluster beams and mass selecting a particular ion for subsequent studies with various photolysis methods such as photodetachment, photofragmentation, and photoelectron spectroscopy. Ga$\sb{\rm x}$As$\sb{\rm y}$ clusters with x + y $>$ 10 thus generated have compositions ranging from Ga$\sb{\rm x+y}$ through Ga$\sb{\rm x}$As$\sb{\rm y}$ to As$\sb{\rm x+y}$ which closely follow a statistical binomial distribution. In the smaller clusters, strong variations were observed from this binomial distribution as a result of kinetic effects in the cluster formation process. An even/odd alternation in the ionization potential (IP) and the electron affinity (EA) of GaAs clusters was observed, which only depended upon the total number of atoms in cluster. GaAs clusters with an even total number of atoms had higher IP but lower EA than their neighboring odd ones. This suggests that the even clusters have fully paired singlet ground states with no dangling bonds. Electron affinities of Si, Ge, and GaAs clusters have been roughly determined as a function of cluster size by detecting the photoelectron intensity dependence upon the probing laser fluence. In general, the EA of cluster increases monotonically with increasing cluster size extrapolating towards the EA of the corresponding bulk semiconductor material. The fragmentation patterns of Si and Ge negative ion clusters observed were remarkably similar, implying that they have almost the same structures. In contrast with GaAs and metal clusters, Si and Ge anions fragmented by fission into mainly 5-10 atom size range, and the six and ten atom anions were the most favorite daughters. Photofragmentation processes were found to be competitive with photodetachment. For Si and Ge, one-photon detachment and one-photon fragmentation occurred simultaneously in certain laser wavelength ranges. Detachment became dominant at high photon energies.

The surface reactivity of germanium is of interest because of novel Si$\sb{x}$Ge$\sb{1-x}$ heterostructure applications and the insight into semiconductor surface chemistry attainable through comparative studies on silicon and germanium. The adsorption of the inorganic hydrides H$\sb2$S, H$\sb2$O, NH$\sb3$, and HX (X = Cl, Br) on Ge(100) was investigated by temperature-programmed desorption (TPD) for the first time. The initial sticking probability $S\sb0$ for H$\sb2$S exhibits at most only a minor temperature effect, remaining roughly constant at $\sim$0.23 within the temperature range 173 K $\le$ T $\le$ 373 K. Adsorbed H$\sb2$S decomposes upon heating into H$\sb2$ and GeS, which desorb at 570 K and 660 K, respectively. The initial sticking probability for H$\sb2$O depends strongly upon substrate temperature, dropping from 0.28 at 173 K to $\sim$0.02 at 273 K. Adsorbed water decomposes to yield H$\sb2$ and GeO, which desorb at peak temperatures of 570 K and 660 K, respectively. Both HCl and HBr adsorb on Ge(100), and desorb upon heating to 570 K as H$\sb2$ and to 580 K as HX in roughly equal proportions. The remaining X(a) desorbs as GeX$\sb2$ at 680 $\sim$ 760 K. The initial sticking probability for HBr is 0.77 at 273 K, falling slightly to 0.55 at 373 K, whereas S$\sb0$ for HCl falls from 0.30 at 273 K to 0.066 at 373 K. The peak shapes and independence of peak temperature with coverage for H$\sb2$ and HX for all adsorbates indicate approximately first-order desorption kinetics, but GeX$\sb2$ desorption follows second-order desorption kinetics. Adsorption of NH$\sb3$ was not observed, implying $S\sb0$ $\le$ 6 $\times$ 10$\sp{-5}$. The adsorption and desorption behavior of these molecules can be understood by regarding the Ge(100) dimer atoms as being linked by a strained double bond and examining analogous addition and elimination reactions of molecular germanium compounds.

The effect of spin fluctuations on the resistivities of 14 different $Fe sb{x}Ni sb{1-x}Zr sb2$ metallic glasses were analyzed in the temperature range from 4.2K to 80K. The corrections to the resistivity due to the superconductivity and quantum interference effects at very low temperatures were performed to obtain the spin fluctuation resistivity, $ rho sb{sf}$, as a function of temperature and composition. It is found that, $ rho sb{sf}$ varies as $T sp2$ at very low temperatures, i.e. below around 20K, and as T at higher temperatures. This confirms the predictions of the two-band model of Kaiser and Doniach and the one-band model of Rivier and Zlatic. The spin fluctuation temperatures for all the compositions, were determined from both models. $T sb{sf}$ calculated from the one-band model were about 30% higher than those calculated from the two-band model. The spin fluctuation temperature is lowest when the system is closest to the magnetic transition and it increases when the amount of magnetic species is reduced in the alloy, i.e. for x = 1, $T sb{sf}$ = 10K (15K) and for x = 0.4, $T sb{sf}$ = 64K (96K) for the two-band (one-band) model.

In the past decade, p-type ZnO material has been investigated extensively. Its properties offer the potential for broad applications including the development of ultraviolet light emitting devices. Although n-type ZnO material is well known and studied for decades, the fabrication method and properties of p-type ZnO material are still to date not clearly understood. / In this report, reproducible p-type ZnO thin films sputtered on glass substrates are reported. On the same substrate, p-type ZnO film is local and surrounded by n-type ZnO regions. The thickness of the films is typically three microns after several hours of deposition by radio-frequency magnetron sputtering technique. Both p-type ZnO and n-type thin films are characterized by optical and electrical measurements at room temperature. / The crystal structure of p-type ZnO is examined by X-ray diffraction patterns. The X-ray diffraction patterns show that the material is polycrystalline and has (100) and (101) preferred orientation. Photoluminescence spectra of ZnO help to identify the energy levels in the material and spectra analysis reveals the presence of defects and dopants in the material. For p-type ZnO, the resistivity, the hole concentration and hole mobility are found to be 148.8 O-cm, 4.34 x 1018/cm3 and 1.72 x 10-2 cm2/V-sec respectively.

In this thesis theoretical investigations of quantum ballistic transport in semiconductor nanostructures is presented. Particular systems under consideration include quantum wire, quantum dot, and combinations of them. Effects of quantum interference, chaotic scattering, inelastic scattering, many-electron interaction, and junction resonance are examined. Conductance of the system is computed as a quantum scattering process, and fluctuations in conductance and magnetoconductance in ballistic structures are investigated in detail under the influence of the above mentioned physical effects. For the resonant transmission process, evidence is presented of the universal statistics satisfied by the quasi-bound states of the system which mediate the scattering. Computational framework is developed to solve the quantum scattering problem in multi-probe structures, and to include Coulomb interactions and other scattering potentials.

In this thesis, we investigate phase behaviors and wetting phenomena in complex fluids. The complex fluid under consideration is a ternary mixture of two immiscible fluids (oil and water) plus a concentration of surfactants. The model used is based on a Ginzburg-Landau functional due to Laradji et al. which is written in terms of an order parameter representing the difference between the local densities of oil and water and a scalar field representing the local concentration of surfactants. A mean field phase diagram for the homogeneous phases was first obtained in terms of the surfactant chemical potential, mu using exact mean field equations. A tricritical point followed by a triple line between an oil/water coexistence region and a disordered phase was established from these equations. Following Laradji et al., the Langevin equations were derived in the presence of a new term in the free energy functional which stabilizes the system at long wavelengths. Once the phase diagram was established, we examined the equilibrium wetting of a water/oil interface by the complex fluid and we calculated the related contact angle, theta, along the triple line as a function of increasing mu. (Abstract shortened by UMI.)