This thesis is devoted to the studies of structural and magnetic properties of Pd/Fe multilayers with the principal goal of determining the extent to which the Pd layers are polarised by the Fe atoms and the average moment induced on each Pd atom. Although Pd/Fe multilayers have been the subject of several previous studies, no consensus on the behavior of magnetically polarised Pd has emerged. This work has the novel feature of applying a wide range of characterization techniques on the same sample. These techniques included x-ray diffraction, conversion electron Mossbauer spectroscopy (CEMS), magnetometry and polarised neutron reflectometry. Ag/Fe multilayers were first characterized to confirm the validity of the analysis of the small-angle x-ray reflectivity to obtain layer thicknesses, as well as to determine the temperature dependence of the Fe moment from GEMS data. / From the intersection of the results from the complementary measurements on Pd/Fe multilayers, for the first time, an unequivocal understanding of the behavior of magnetically polarised Pd has been achieved. We find, there is a clear excess magnetisation associated with Pd polarisation. At 4.5 K, the Pd in contact with an Fe surface is polarised with an average moment of 0.32 +/- 0.02 muB to a depth of 20 +/- 4 A (9 +/- 2 atomic layers). These results indicate a large exchange splitting of the Pd d-bands for a significant distance from the Fe surface, leaving the spin-up band full, and a moment in the Pd arising from the 0.36 holes in the spin-down band. We also find that the Fe moment at the Pd/Fe interface is slightly enhanced to 2.42 +/- 0.05 muB for about 2.0 +/- 0.3 atomic layers, suggesting that the magnetic properties of Fe is less affected by Pd as compared to the influence of Fe on Pd. Neither the extent of Pd polarisation nor the interface Fe moment agree with values predicted by theoretical calculations (the calculated Pd polarisation depth is 2 atomic layers, and the interface Fe moment is 2.7 muB). The band structure calculations will have to be refined in the light of the results from current study.

In this thesis, an overview of non-equilibrium Green's function (NEGF) technique is presented. The entire formulism is derived from the starting point of the definitions of Green's functions. The special application of NEGF to transport problems is discussed in details. A brief introduction of Kondo phenomenon and several theoretical approaches are presented. Using the knowledge of NEGF and Kondo problem in general, we investigated the Kondo phenomenon in double quantum dots (DQD) in great detail. In this application, the physical quantities are derived in terms of Green's functions and self-consistent equations determining the state of the system are solved numerically. A phase diagram is presented as the result of competition between Kondo effect and magnetic exchange interaction, and spin flipping scattering center in the DQD system is shown to have great effect as it breaks the coherence between the two QDs under certain circumstances.

Bismuth (Bi) is a unique electronic material with small effective mass (∼0.001me) and long carrier mean free path (100 nm at 300K). It is particularly suitable for studying nano scale related phenomena such as size effect and energy level spacing. In this thesis work, bismuth based nanoelectronic devices were studied. Devices were fabricated using a combination of electron beam (e-beam) writing and thermal evaporation techniques. Dimensions of the fabricated devices were in the order of 100 rim. All structures were optimized for individual electrical characterization. Three types of devices were studied: Bi nanowires, Bi nanowires with dual side-gate structures and Bi nanodot structures. In the study of Bi nanowires, metal-to-semiconductor transition phenomenon and size effect were observed. The conduction behavior of Bi nanowires changed from metallic to semiconductor when the device's critical dimension was reduced to below 50 nm. It is a solid experimental evidence of the quantum confinement-induced bandgap theory. Additionally, it has been found in the present work that resistivity of individual Bi nanowire increased as linewidth decreased indicating size effect occurred in the Bi nanowires. Dual side-gate structures were formed adjacent to the Bi nanowires in an attempt to modulate the current. Measurements showed a 7% of current modulation. The small current modulation suggested the high carrier density in the nanowire which has prevented the full depletion of free carriers. 100 nm-diameter Bi nanodot structures were fabricated utilizing proximity effect of e-beam writing. Precise control of electron doses and process conditions led to the successful fabrication of sub-nanometer tunneling junctions to the nanodots. Significant non-linear current-voltage (I-V) characteristic was observed at low temperatures. The step like I-V characteristic was a strong indication of energy level spacing in the zero-dimensional nanodot structure. The successful observation of energy level spacing in a relatively large nanodot is due to the small effective mass of bismuth material which leads to a measurable energy level spacing.

Over the past several decades, semiconductor electronic devices have been miniaturized following the remarkable "Moores law". If this trend is to continue, devices will reach physical size limit in the not too distance future. There is therefore an urgent need to understand the physics of electronic devices at nano-meter scale, and to predict how such nanoelectronics will work. In nanoelectronics theory, one of the most important and difficult problems concerns electron-phonon interactions under nonequilibrium transport conditions. Calculating phonon spectrum, electron-phonon interaction, and their effects to charge transport for nanoelectronic devices including all atomic microscopic details, is a very difficult and unsolved problem. It is the purpose of this thesis to develop a theoretical formalism and associated numerical tools for solving this problem. / In our formalism, we calculate electronic Hamiltonian via density functional theory (DFT) within the nonequilibrium Green's functions (NEGF) which takes care of nonequilibrium transport conditions and open device boundaries for the devices. From the total energy of the device scattering region, we derive the dynamic matrix in analytical form within DFT-NEGF and it gives the vibrational spectrum of the relevant atoms. The vibrational spectrum together with the vibrational eigenvector gives the electron-phonon coupling strength at nonequilibrium for various scattering states. A self-consistent Born approximation (SCBA) allows one to determine the phonon self-energy, the electron Green's function, the electronic density matrix and the electronic Hamiltonian, all self-consistently within equal footing. The main technical development of this work is the DFT-NEGF-SCBA formalism and its associated codes. / A number of important physics issues are studied in this work. We start with a detailed analysis of transport properties of C60 molecular tunnel junction. We find that charge transport is mediated by resonances due to an alignment of the Fermi level of the electrodes and the lowest unoccupied C60 molecular orbital. We then make a first step toward the problem of analyzing phonon modes of the C60 by examining the rotational and the center-of-mass motions by calculating the total energy. We obtain the characteristic frequencies of the libration and the center-of-mass modes, the latter is quantitatively consistent with recent experimental measurements. Next, we developed a DFT-NEGF theory for the general purpose of calculating any vibrational modes in molecular tunnel junctions. We derive an analytical expression for dynamic matrix within the framework of DFT-NEGF. Diagonalizing the dynamic matrix we obtain the vibrational (phonon) spectrum of the device. Using this technique we calculate the vibrational spectrum of benzenedithiolate molecule in a tunnel junction and we investigate electron-phonon coupling under an applied bias voltage during current flow. We find that the electron-phonon coupling strength for this molecular device changes drastically as the bias voltage increases, due to dominant contributions from the center-of-mass vibrational modes of the molecule. Finally, we have investigated the reverse problem, namely the effect of molecular vibrations on the tunneling current. For this purpose we developed the DFT-NEGF-SCBA formalism, and an example is given illustrating the power of this formalism.

A system for the deposition of metallic electrodes on KBr under ultra-high vacuum conditions has been designed and fabricated. Stencil masks and membranes 4-5 mum thick are fabricated on silicon chips have been created using wet etching in tetramethyl ammonium hydroxide (TMAH) with a boron etch stop. A holding system for UHV has been designed and built with a modified sample holder for performing electrical measurements on samples. The UHV system contains an AFM, STM, and SEM for surface examination and characterization. The growth of metals on KBr was examined using a separately constructed sample holder under high vacuum. Examination of 2.5 and 5 nm tantalum and 20 nm gold films using AFM and SEM revealed significant differences in the film growth and quality. Tantalum films appeared to be continuous, though possessing significant buckling whereas gold films have significant voids and poor edge definition around simple masks.

In this thesis, we present a theory to calculate the time-dependent current flowing through an arbitrary noninteracting nanoscale phase-coherent device connected to arbitrary noninteracting external leads, in response to sharp step- and square-shaped voltage pulses. Our analysis is based on the Keldysh nonequilibrium Green's functions formalism, and provides an exact analytical solution to the transport equations in the far from equilibrium, nonlinear response regime. The essential feature of our solution is that it does not rely on the commonly used wideband approximation where the coupling between device scattering region and leads is taken to be independent of energy, and as such provides a way to perform transient transport calculations from first principles on realistic systems, taking into account the detailed electronic structure of the device scattering region and the leads. As an illustration of the general theory, we perform a toy model calculation for a quantum dot with Lorentzian linewidth and show how interesting finite-bandwidth effects arise in the time-dependent current dynamics. Finally, we describe possible generalizations of our theory to the cases of superconducting leads (an example of broken symmetry) and one-dimensional leads in the Luttinger liquid regime (an example of an interacting system).

Noncontact atomic force microscopy (NC-AFM) was applied to investigating the creation of monatomic depth rectangular pits, the growth of metals, and the templated growth of molecules on the KBr (001) surface under ultrahigh vacuum conditions. The pits were produced by a new method where the sample is exposed to a controlled dose of charge from an electron beam evaporator. The structure and size distribution of the pits was characterized by NC-AFM. For the metal growth studies, gold, tantalum, and palladium were deposited onto KBr by electron beam deposition. The gold produced tall multiply twinned and epitaxial nanoparticles, while the tantalum formed flatter fractal islands. The palladium growth resulted in the creation of rectangular KBr islands in addition to palladium nanoparticles. Despite the use of a charge deviating grid, charge played an important role during the metal growth. In particular, the number density of gold nanoparticles followed nearly the same temperature dependence as the pits, suggesting that the metal nanoparticles nucleate predominantly at defect sites created by incident charge. The effect of charge was also seen in the tantalum system where pits surrounded the nanoparticles prepared at elevated temperatures. By creating pits before depositing gold, it was shown that the pits edges can be used to template the growth of metals. It was also shown that the pits can be used to trap PTCDA molecules and to align C60 molecules with the <100> direction of the substrate. Molecular resolution NC-AFM measurements were used to determine the structures and lattice constants of the molecular nanostructures. Experiments involving the sequential growth of metals and molecules showed that the order of deposition and the strength of the molecule-metal interaction are key factors in determining the nature of the growth. Furthermore, it was shown that metal structures can be used to nucleate the growth of sufficiently strongly interacting molecules.

The AC phase-coherent transport in mesoscopic structures is studied via a scattering approach. A general theory is presented under the guidance of two physical principles: charge and current conservation, gauge invariance. As the AC response is intrinsically a many-body problem, we have to treat the scattering problem and the charge redistribution effects in a self-consistent manner. / One quantity of particular interest is the mesoscopic capacitance. In mesoscopic structures where the electric screening length is comparable to the geometric size, the experimentally relevant capacitance is no longer due to geometry alone but to the electro-chemical potential and the capacitance crucially depends on the density of states of the conductor. Furthermore, the phase-coherent nature of the carrier motion leads to striking asymmetric effects in the magneto-capacitance. The general theory is put forth into numerical simulations where the theory is justified. / The study of AC transport in mesoscopic structures should not only help us to better understand the physics of many-body systems, but should also provide valuable knowledge in characterizing and controlling small electronic devices which is of great technological importance.

The effect of composition on the mechanical properties of high Al content Al-Y-Ni metallic glasses has been studied. Nine samples in all were prepared with a composition of ${ rm Al sb{85}Y} sb{x}{ rm Ni} sb{15-x}({ rm x}=3, ...,11).$ The amorphous alloys were first tested using both XRD and DSC. The DSC runs revealed that the samples were made up of two different types: one showing no glass transition and a lower crystallization temperature, and the other showing a distinct glass transition with a higher crystallization temperature indicating that they are truly homogeneous glasses. The samples showed a Young's modulus that does not seem to reveal any distinct compositional dependence whereas, the tensile strengths showed a distinct decreasing trend with increasing Y content. Values of various mechanical properties and crystallization temperatures obtained in this study are compared to those reported by other groups. We find very high specific strengths in these glasses, which combined with their excellent ductility makes them ideal structural materials. The effect of annealing is also examined and it is found that the samples lose a large proportion of their tensile strength and ductility when annealed.

Previous studies on Al85Yx Ni15-x glasses established a correlation between crystallization mode (pure growth versus nucleation and growth) and crystallization product. Glasses with approximate compositions x = 5, 7, 8, 10 were studied in order to accurately ascertain the nature of the structural variance which gives rise to different crystallization modes and the identity of the resulting crystallization products. Glasses with x = 5, 10 have a clear distinction: x = 5 contains quenched-in Al nanocrystals which act as nucleating centers leading to alpha-Al as the first crystalline product; equilibrium crystalline phases are alpha-Al, Al3Ni and a stacking variation of Al4YNi. x = 10 is a homogeneous glass which undergoes a glass transition prior to crystallization; first crystalline product is an unstable FCC structure which breaks down via Al segregation; equilibrium phases are alpha-Al, beta-Al3Y and Al16YNi 3. x = 7,8 share these characteristics: x = 7 contains quenched-in Al-nanocrystals and follows the initial x = 5 pattern of primary Al crystallization; however it undergoes a glass transition prior to first stage crystallization and equilibrium phases are alpha-Al, beta-Al3Y and Al16YNi3. x = 8 crystallizes by nucleation and growth yet has identical crystallization products as the corresponding x = 7 crystallization stages. Isothermal annealing prior to first two crystallization stages of x = 8 yields alpha-Al and the unstable FCC structure. Isothermal crystallization is complex, frequently involving the overlap of multiply nucleating phases and the sequential nucleation of successive crystallization stages at the same annealing temperature. The results of these crystallization studies imply that Al-Y-Ni glasses obey the cluster model (Al-Y versus Al-Ni clusters) where cluster-cluster correlation establishes the degree of medium-range order and presence or absence of Al nanocrystals. (Abstract shortened by UMI.)