The electronic contribution to the resistivity rho and its temperature dependence were investigated for amorphous and crystalline [Fe xCo1--x] 33.3Zr66.7 (0 ≤ x ≤ 1) alloys in the temperature range 80--300 K. As Fe-rich compositions may exhibit spin fluctuation effects, transport properties were not studied below 80 K where spin fluctuation effects must be taken into consideration. The compositional and structural integrity of the samples was verified by means of X-ray diffractometry, electron-microprobe analysis, and differential scanning calorimetry. It was also confirmed that the first crystallization product for all the compositions is the face-centered cubic phase with the NiTi2-type structure. A true comparison between amorphous and crystalline transport properties was thus possible. For the metallic glasses, it was observed that rho( T) had a temperature dependence of the form: A + Bexp(--T/Delta) in agreement with Mizutani who proposed this relation for glasses containing a significant number of d-electrons at EF. The characteristic temperature, Delta, was found to be related to the Debye temperature, theta D, and the parameter B to the electronic specific heat coefficient, gamma. The resistivity data for the crystalline tenary compounds exhibited a (c -- bT + aT2)-dependence. Both the glasses and their crystalline counterparts were characterized by negative temperature coefficients of the resistivity, alpha. However, for the glasses, alpha increased as the Fe content increased whereas for the crystalline compounds alpha decreased as the Fe content increased.

The general theory of first principles calculations is presented and all equations are derived from basic starting points. In particular, an explanation of density functional theory (DFT) is given, with emphasis on the Hohenberg-Kohn theorem, the Kohn-Sham equations and the local density approximation (LDA). In addition, a description of pseudopotentials, basis sets, self-consistency, and solution methods for the Kohn-Sham equations will also be presented. Using these basics as a foundation, the equations needed to conduct an atomic orbital first principles calculation are then derived. This method incorporates the Harris approximation, LDA, a minimal sp3 atomic orbital basis set, and diagonalization to solve the Kohn-Sham equations. Finally, this technique is implemented and used to conduct calculations on small Si and Al clusters, bulk Si phase diagrams, Si band structures, Si(100) surface reconstruction, Al(111) surface relaxation, Si6 stability on the Si(100)2 x 1 surface, and Al nanowires.

We have used thermal conductivity measurements at low temperature to probe the behavior of the unconventional superconductor YBa2Cu 3O7-delta (YBCO). Two aspects were investigated: (1) the in-plane anisotropy, studied in order to gain insight into the contribution of CuO chains, and (2) the effect of a magnetic field, investigated in order to explore the contribution of vortices. Our results on the low temperature thermal conductivity are in good quantitative agreement with the theory for a d-wave superconductor. We have found a very weak (or even negligible) anisotropy suggesting that the anisotropy could not simply be explained by mass tensor anisotropy or the plasma frequency anisotropy. The magnetic field studies revealed an increase in the residual linear term (kappa/ T as T → 0) with field, reflecting the contribution to the density of states from the extended quasiparticles due to their Doppler shift in the presence of vortices. These results are in good quantitative agreement with the theoretical predictions.

The crossover transport regime between the quantum Hall effect and the Aharonov-Bohm effect is studied in terms of Buttiker's approach of electrical conduction. Quantum Hall effect and Aharonov-Bohm effect are very important effects in mesoscopic physics and both demonstrate unambiguously that quantum mechanics is the dominant factor in nanoscale electrical transport problems. However, they belong to situations of different dimensionality and different strength of magnetic fields. Our goal is to reveal the physics at the crossover regime between the two and find the transport properties of this transition regime. / We have computed Hall resistance of a four-probe box-shaped quantum dot with an artificial impurity confined inside. As the size of the impurity is increased, transport behavior changes from the usual quantum Hall regime to a regime dominated by strong Aharonov-Bohm (AB) oscillations. We observe directly the formation and coupling of the edge states and their effects on the Hall resistance, by varying a magnetic field. For a range of the impurity size, transport enters the crossover regime where quantum Hall and AB effects compete, and a peculiar approximate symmetry between various transmission coefficients lead to a Hall plateau before the quantum Hall regime is reached. This symmetry can be explained based on scattering matrix theory and a topological equivalence of the dominating transmission patterns where well defined edge states are formed. Finally we investigate the universality of the observed symmetry property in several other structures and find that within the scope of our calculation the symmetry is universal.

In this work we have re-examined the classical problem of nucleation and growth. We present a new model that combines steady-state homogeneous nucleation theory with the classical Lifshitz-Slyozov mechanism of growth. This model considers the substantial correlations between droplets and naturally incorporates the crossover from the early-stage, nucleation dominated regime to the scaling, late-stage, coarsening regime within a single framework, without ad-hoc assumptions. This is achieved by the development of a set of self-consistent interface equations which describe the decay of metastable states. The model is implemented numerically and some interesting dynamical behaviour is observed, including the reproduction of the expected late-time scaling and power-law growth laws for the key mean-field variables.

One of the central problems of molecular electronics is to understand electron conduction properties when a functional molecule is interfaced with external electrodes and put under external bias and gate potentials. These properties are influenced by the molecule-electrode interaction as well as by the structure of the functional region of the device. In this thesis, we investigate from first-principles the transport properties of a number of molecular-scale systems, and try to relate the observed features to both the atomic and electronic structure. / We start with a detailed analysis of transport through carbon atomic wires, and find that the equilibrium conductance is sensitive to charge transfer doping, and that the I-V characteristics exhibit negative differential resistance at high bias due to a shift of conduction channels relative to the states of the electrodes. / Using a Sc3N C80 metallofullerene device, we address several general questions about quantum transport through molecular systems and provide strong evidence that transport in such molecular devices is mediated by molecular electronic states which have been renormalized by the device environment. / The possibility of inducing nuclear dynamics in single-molecule Au-C 60-Au transistors via inelastic, resonance-mediated tunneling current is examined using a method based on the combination of a theory of current-triggered dynamics[1] and our nonequilibrium Green's function approach of computing electron transport properties. / We investigate several single molecule field-effect transistors consisting of conjugated molecules in contact with metallic electrodes. The source-drain current is found to be sensitive to the external gate potential and the molecular structure; with modulations of the current as large as several thousand fold. / Given a proposed operation principle, we obtain quantitative results on the rectification properties for an organic molecule rectifying diode. The I-V characteristic shows clear rectification behavior, and is explained from the simple picture of shifting of molecular levels due to substituents and an externally applied bias voltage. / Finally, we report a formulation combining density functional theory with the Keldysh nonequilibrium Green's function, for calculating quantum mechanical forces under external bias and during electron transport. We present an example force calculation consisting of a single atom point contact.

Atomic scale structures are studied using first principles or ab initio simulations. We first review the formalism required for a typical calculation and then proceed to examine a few applications. All the simulations were performed using plane wave based pseudopotential methods and by a direct minimization of the Kohn-Sham total energy functional. / Using this method, we have investigated the effect of impurity atoms like boron, sulphur and phosphorous on the adhesive properties of two aluminium minimum slabs. We found that both sulphur and phosphorous (both substitutional impurities) decreased the adhesive energy and the interfacial strength, while boron (an interstitial impurity) increased the interfacial strength marginally. It was also found that the impurities act as spacers and increase the interfacial spacing. This increase was found to increase with atomic size. These observations are consistent with experimental work. / We have also investigated the possibility of using orbital-free kinetic energy functionals in ab initio simulations. Various functionals, their limiting forms and response properties were studied. The results obtained using this method agree well with full Kohn-Sham calculations. This was demonstrated using a variety of systems (Si clusters, H$ vert$Si(100), c-Si). The excellent scaling properties of the method was illustrated with a simulation of the interactions between a tip and substrate (150 atoms). The normal forces experienced by the small cluster serving as the tip were used to map out the top surface of the substrate. An ad hoc scheme to incorporate pseudopotential non-locality into the orbital-free formalism was also proposed and tested.

The magnetic properties of amorphous Fe$ sb{ rm x}$T$ sb{ rm 100-x}$ (T = Zr, Hf, Sc; 89 $ le$ x $ le$ 93) alloys have been systematically studied mainly by Mossbauer spectroscopy and magnetization measurements. Two magnetic transitions have been observed in Fe$ sb{92.5}$Hf$ sb{7.5}$ (the only FeHf alloys studied here) and FeZr alloys with Fe content between 90 and 93 at.%. We have ruled out the cluster models which attribute the second transition either to the ordering of AFM clusters or to the freezing of FM clusters, and confirmed that the second transition is due to the homogeneous freezing of the transverse spin components as a result of exchange frustration. On varying the frustration level, the evolution process from a ferromagnetic to a spin glass ordering has been observed. Fe$ sb{89}$Zr$ sb{11}$ essentially exhibits conventional ferromagnetic behavior, while Fe$ sb{90}$Zr$ sb{10}$ shows two magnetic transitions with a noncollinear ground state. As we increase the Fe content further (and thus raise the frustration level), the second transition temperature T$ sb{xy}$ and the noncollinearity of the ground state increase, whereas the first transition temperature T$ sb{c}$ drops. T$ sb{xy}$ and T$ sb{c}$ are expected to meet at x $ simeq$ 94.5, suggesting that Fe$ sb{94.5}$Zr$ sb{5.5}$ (which can not be made by melt-spinning) would be a spin glass. Fe$ sb{91}$Sc$ sb9$ is the most frustrated system studied here and it exhibits a single transition to a spin glass. Extrapolation of the magnetic properties of all systems gives a common limit as the Fe concentration approaches 100%, and suggests that amorphous Fe is a spin glass with the spin freezing temperature about 100K and an average iron moment of $ sim$1.6$ mu sb{B}$. Below the second transition, the transverse spin components are strongly correlated on a nearest neighbor scale in Fe$ sb{92}$Zr$ sb7$Sn, while the correlation length of the longitudinal components shows no detectable change on the local scal

A spectrometer was built for the purpose of performing Depth Selective Conversion Electron Mossbauer Spectroscopy (DSCEMS) on surfaces containing iron nuclei. The spectrometer was based on a Retarding Field Analyzer design by van Noort and van Gorkum$ sp1$. It has an acceptance angle of 5% of 4$ pi$, and is capable of energy resolutions of between.8% and 4.3% of the pass energy. The spectrometer is suited for samples with a diameter as large as 10 mm. The designing and dimensioning processes, construction, operation, and performance of the spectrometer are presented here.

In November 2002 a Microfabrication Lab was established in the physics department of McGill University to support research in nanoscience and technology. At the same time, I arrived at McGill to begin my graduate study. So I was assigned to do research on microfabrication, especially bulk wet etching of silicon using TetraMethyl Ammonium Hydroxide (TMAH). / The content of microfabrication is quite broad, and also very useful in both industry and academic. Since our fab is a newly built one and I had no experience in this area before, this thesis mainly included some basic processes in microfabrication, such as the photolithography, wet etching, reactive ion etching, and soon. Also it compared the wet etching with dry etching. Some results of TMAH wet etching were showed in the thesis, which agreed well with that of the other groups. A simulation program was developed to predict the etching result of TMAH and it appeared to work well. Finally, based on the knowledge and experience acquired, processes in making cantilever and tip structures, which are critical in the scanning probe microscopes, were developed. Silicon oxide cantilevers with length of 100-200 mum, width of 30-50 mum, and thickness of 1 mum were obtained. Pyramid like silicon tips were also fabricated using the wet etching.