An ultra high vacuum chamber was constructed to study thin film growth using scanning tunneling microscopy (STM). The sample stage is specially designed so that samples can be transferred in situ among various film preparation techniques. For first studies, Ru thin films were deposited at sub-monolayer coverages on C(0001) substrates. From our STM studies, it is found that Ru diffuses easily along the graphite surface, that Ru atoms tend to nucleate at defect sites, and that the first monolayer of Ru grows homogeneously on graphite. These results are in agreement with our recent Auger electron spectroscopy data.

I show that the difference in 'spin up' and 'spin down' angular intensities of electrons emitted from inner core levels of atoms in a magnetic crystal is a spin hologram. Its inverse 'pictures' the component of the spins in the neighborhood of the emitter in the direction that the detected electrons are spin analyzed. Measuring the spin difference in three orthogonal directions determines a vector hologram which gives an image of the atomic spin vectors. I develop the theory and illustrate the feasibility and potential of this novel technique by means of model calculations. Furthermore, I give a detailed treatment of the elastic scattering processes that are responsible for the spin holograms, and study the effect of multiple scattering and self-interference which could cause complications.

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 to be studied 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 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. Energy-integrated electron spin-polarization (ESP) measurements for Pd(110) and energy-resolved ESP measurements for Cu(100) surfaces under a variety of conditions indicate that metastable atom-surface interactions are more complex than has been assumed in past MDS studies. Spin-polarized MDS has also proven useful in the study of surface magnetism. The present work includes a study of the surface electronic and magnetic structure of the Fe(110) surface. Results indicate an interesting reversal of surface electron spin-polarization for Fe(110) surfaces exposed to oxygen.

Photoelectron spectra of negatively charged cobalt clusters in the size range of 4-26 atoms have been obtained. The electron affinity (E.A.) values along with the reported ionization potential (I.P.) have been used to understand the reactivity of neutrally charged cobalt clusters, with H$\sb2$, in terms of their valence electronic structure. Comparison to currently available theories indicate that a charge transfer mechanism (be it from metal to H$\sb2$ or the reverse process) is inadequate in properly explaining the reactivity behavior of these clusters. A third factor, that of Pauli Repulsion, has been found to be significant in controlling the reactivity. An excellent correlation is observed between the promotion energy (E$\sb{\rm p}$) and the observed reactivity of the neutral clusters.

The heat transfer in electrically insulating thin film materials is predominantly governed by phonons and is accurately described when the phonon mean free path is either much smaller than the order of the thickness of the material (the thick limit) or when there is no phonon scattering (the thin limit). The thick limit model, which is referred to as Fourier's equation, and the thin limit model, which is referred to as the Casimir limit, differ primarily in the distribution function used to describe the excitation state of phonons. This difference arises because scattering alters the excitation levels of the phonons. Whereas the Fourier's equation phonon distribution function is derived using the Boltzmann transport equation, the Casimir limit phonon distribution is given by the Bose-Einstein statistics. This paper first relates the elastic properties of a solid to the phonon description of a crystal's energy to obtain the phonon distribution using the Boltzmann Transport Equation. It will then explain why Fourier's equation breaks down at the nano/microscale level and develop a general heat flux equation which also describes the regime between the Casimir limit and Fourier's Equation.

Development of a low-energy electron-spin-polarized He$\sp+$ ion source is described. The ion source uses an optically pumped rf discharge. Metastable He(2$\sp3$S) atoms are produced by electron impact in the discharge and then are optically pumped into the M$\sb{\rm j}$(M$\sb{\rm s}$) = +1 or $-$1 magnetic sublevels by circularly polarized radiation from a Ti:sapphire laser operating at 1.083 $\mu$m. He$\sp+$ ions are produced by Penning ionization in metastable-metastable collisions and should be spin-polarized because of spin conservation in such processes. A method for accurately determining the net polarization of He(2$\sp3$S) atoms in the discharge by measuring the absorption of light from a tunable diode laser is described. This method can be used to optimize source performance. Optically pumping the discharge on the D0, D1, or D2 transitions gave polarizations of 31.2%, 47.1%, and 18.2%, respectively. It is expected that optically pumping the discharge on the D1 transition will produce $\sim$80+% polarization of the metastable atoms after suitable optimization of operating parameters.

We present calculations of the broadening and the shifts of the Rydberg electron levels of a Xenon atom near a metal surface. The Xenon atom is described using a pseudopotenial. The energies and widths of the Xenon states, computed from the Schrodinger equation using the complex scaling method, exhibit a complicated distance dependence. We show that some of the orbitals hybridize, when the atom approaches the surface. This effect even causes the widths of some states to decrease with decreasing atom-surface separation.

Actinide materials are systems rich in interesting physics, while playing an important role in environmental preservation, and a good comprehension of their electronic structure is therefore of particular importance. A first-principles computational methodology is proposed in this work, affording accurate density functional theory studies in such strongly-correlated crystalline systems. The main ingredient behind the success of this approach is the use of hybrid density functionals, which provide good agreement with known experimental data for the optimum structural and electronic properties of the actinide oxides considered in this study. The predictive capabilities of the method help understand certain unusual properties and phenomena associated with these compounds, from puzzling experimental findings to the relative stability of heavy actinide oxides. Plutonium dioxide is taken as a case study in this work and detailed structural investigations are considered for this compound, such as the effects of non-stoichiometry and of various lattice distortions. The interstitial oxygen in PuO2.25 for example is found to be singly charged, consistent with experimental observations and contrary to the O2- previously proposed theoretically. A tetragonal distortion of the PuO2 lattice, with a very small orthorhombic component, is energetically favorable in our description at zero temperature. Such lattice deformation anticipates the experimentally observed orthorhombic phase, to which many actinide dioxides transform at high pressures. We also confirm that non-hydrostatic effects could be responsible for the intriguing value of the only measurement to date of the bulk modulus of PuO2. Unexpected f orbital populations are predicted in heavy actinide dioxides, and they could elucidate certain perplexing structural measurements made on these compounds. These occupancies point to an early-occurring half-filled shell effect, and can also explain the lack of experimental evidence for the heavier actinide dioxides. These findings suggest that accepted models of electronic structure for certain open-shell compounds are not always warranted, and that their theoretical descriptions should be revised accordingly.

Part I. We have investigated theoretically the interactions and phase transitions of arrays of magnetic nanoclusters embedded in nonmagnetic metals and semiconductors. Two nanoclusters of ferromagnetic elements embedded in a nonmagnetic semiconducting material are expected to be coupled magnetically if the nanoclusters are large enough and the semiconductor is sufficiently doped to provide enough electrons, since the latter mediate the indirect magnetic interactions between the nanoclusters. Apart from its potential technological applications, such as giant magnetoresistance for non-volatile memory applications, and DMS (diluted magnetic semiconductors) for combined process and storage devices, this study is of fundamental interest. As a consequence of the temperature dependence of the indirect interactions, it is shown that for semiconductors several ferromagnetic phase transitions are possible depending on the size of the nanoclusters, whereas for metals a single ferromagnetic phase transition occurs independently of the size of the nanoclusters. The critical temperature and spontaneous magnetization of the network of nanoclusters are evaluated in all cases. Part II. We have found evidence for surface acoustic wave (SAW) propagation of a lithium niobate (LiNbO3)/diamond/silicon multilayer structure. Devices with higher-frequency response and low insertion loss as well as smaller sizes and weight are required for telecommunications. Theoretical calculations had predicted that LiNbO3 thin films on diamond/silicon substrates have both high SAW propagation velocities and high electromechanical coupling coefficients. Metallo-organic decomposition (MOD) and rf-sputtering techniques are used here to grow LiNbO3 thin films on diamond/silicon substrates. These thin films are characterized by XRD, AFM, and interferometer. SAW filters are fabricated by depositing interdigital transducers (IDTs) onto the LiNbO3/diamond/silicon films. Microwave characterizations, such as frequency response, are done by using network analyzer test sets. The impulse response in the time domain is calculated by fast Fourier transforms. Evidence for SAW activity is found for this multilayer structure. Integrating a composite structure of a piezoelectric layer and a high acoustic-velocity layer onto silicon substrates thus shows promise as a way to increase the operating frequency for wireless-telecommunication applications.

A spin polarized He$\sp+$ ion source has been developed to study the dynamics of ion-surface interactions. The He$\sp+$ ions are produced by Penning ionization in collisions between electron-spin-polarized He(2$\sp3$S) metastable atoms contained in a weak rf-excited discharge. The ions are extracted from the discharge and focused onto clean or adsorbate-covered surfaces using a series of electrostatic lenses. The impact energy can be varied from $\rm{<}10eV$ to $\rm{\ge}650eV$ and typical beam polarizations are 10-15%. Information about ion/surface interactions, and the dependence of those interactions on the incident ion energy, is obtained by measuring the energy distribution and polarization of electrons ejected from the surface as a result of Auger neutralization.