In an attempt to understand how surface contacts affect friction, and to bridge the gap between single contact and large scale friction studies, silicon and PDMS multi-tip arrays were produced in the McGill Microfabrication Facility. An apparatus was constructed to rub the tip arrays on a glass surface while creating a diffraction pattern using scattered laser light. Changes in tip ordering could be correlated to changes in the diffraction pattern. Values for tip-to-tip separation were extracted from the diffraction pattern and it was found that the PDMS tip array compressed by 10% after sliding. / Simulations of an AFM tip rubbing along an ionic surface were also performed. Experimentally observed stick-slip behavior was reproduced in the simulation, and simulated contact stiffness values corresponded to experimental results. By varying the flexibility of the tip and the surface it was determined that tip compliance is the dominant factor that controls stick-slip behavior.

Avalanche Photodiode (APD) is a compact and rugged device, with single photon detection capability and high quantum efficiency. It is a good candidate as a detector to observe irradiation damage to silicon devices and the irradiation induced defects. In this thesis, we have observed the bistable defects and the multistable defects in the APD. We can also observe the time evolution of defect formation and annihilation with time resolution of 10 ms. Also we develop a technique to observe the evolution of defects in real time with an improved time resolution of 1 $ mu s$.

The thermal conductivity $ kappa$ of the high-temperature superconductor $ rm YBa sb2Cu sb3O sb{7- delta}$ has been the subject of numerous investigations in recent years. Previous measurements show that $ kappa$: (1) exhibits a large peak in the superconducting state; (2) is anisotropic in the basal plane of the orthorhombic crystal structure. The main two subjects of this thesis are: (1) the origin of the peak and (2) a detailed investigation of the anisotropy. / In order to investigate the relative contribution of electrons and phonons to the heat conduction in YBCO, we have measured the thermal and electrical conductivities of high-quality twinned and detwinned crystals, with different levels of Zn-doping (from 0% to 3%). We found that the peak was rapidly suppressed by the impurities. Two scenarios are used to explain our results, attributing the effect to decrease in the carrier mean free path of either the electrons or the phonons. / As for the anisotropy between the a-axis and the b-axis, only two previous studies had previously been done. We find some new striking features: (1) a peak appears in $ kappa sb{chain}$ below 50 K, revealed as a result of our using of higher purity samples. (2) this peak is similar to that of $ kappa sb{a}$ below $T sb{c} (i.e., kappa sb{plane}),$ which we take as the evidence for the growth of superfluid density in the chains below 60 K. We discuss these results in terms of a model of single-electron tunneling between chains and planes.

We examine tracer diffusion in lipid bilayer membranes containing either cholesterol or lanosterol, using a random lattice Ising model. Specifically the model is a two-state off lattice tethered network of hard disks which is dynamically triangulated and the interactions between the hard disks are only effective along the tethers linking the disks. The model was already applied to lipid-sterol systems and was successful in reproducing the phase diagrams and related physical properties. In this thesis we apply this model in conjunction with Monte Carlo simulation methods as follows. We calculate the diffusion constant for lipid-cholesterol and lipid-lanosterol bilayer membranes both as function of temperature and sterol concentration in all accessible regions of the relevant phase diagrams. Comparison with experiment and comments on sterol related evolution are included.

Rb-IV is the stable high-pressure phase of rubidium between 16 and 21 GPa. The structure of Rb-IV has long been known to be complex, but it is only recently that it has been solved as being an incommensurate host-guest composite structure, comprising a tetragonal host framework containing chains of "guest" atoms that form structures incommensurate with the host along their common c- axis. While similar composite structures have been observed in a number of other elemental metals, Rb-IV is unique in that on pressure decrease below 16.7 GPa at 300 K, the chains of guest atoms become disordered and liquid-like. This thesis is a detailed structural study of Rb-IV. High-pressure, combined with high-temperature powder diffraction techniques, have been used to map the P-T phase diagram of rubidium between 15 GPa and 20 GPa and between 298 K and 600 K. The results show that the guest order-disorder transition pressure is strongly temperature dependent, and that the disordered phase is observed to the highest temperatures. Technical developments, which have made it possible to extract reliable modulation reflection intensities from a Rb-IV single crystal, are described. The resulting data are used for a full modulated structure refinement of Rb-IV, revealing a saw-tooth shaped modulation of the guest structure, from which new information on the host-guest interactions has been extracted. Inelastic X-ray scattering techniques have been used to measure the longitudinal acoustic (LA) phonons in a Rb-IV single crystal. Two LA-like phonon branches, one for each of the two composite subsystems, are observed along the common c-axis. The sound velocities in the host and guest structures are determined and the pressure dependence is shown to differ by a factor of two. Finally, developments that will enable future combined high-pressure high- temperature single-crystal diffraction studies, and single-crystal diffraction studies at pressures above 100 GPa, will be presented.

<p> Recently the theoretical discovery of single channel quantum dragons has been reported. Quantum dragons are a class of nanodevices that may have strong disorder but still permit energy-independent total quantum transmission of electrons. This thesis illustrates that multi-channel quantum dragons also exit in rectangular nanotubes and provide an approach to construct multi-channel quantum dragons in rectangular nanotubes. Rectangular nanotube multi-channel quantum dragons have been validated by matrix method based quantum transmission calculation. This work could pave the way for constructing multi-channel quantum dragons from more complex nanostructures such as single-walled zigzag carbon nanotubes and single-walled armchair carbon nanotubes.</p>

<p> Studies were performed on two seemingly different topics, molecular thin films on graphite/graphene and metal induced changes in various cuts of silicon (Si) surfaces. However, both projects share the underlying theme of self-assembly. Since nature can rely upon self-assembly at the nano-scale, all that is needed is to discover functional means to create components for integrated circuits as well as electronic and photonic devices. </p><p> Scanning Tunneling Microscopy and Spectroscopy (STM/STS) studies were carried out to characterize the morphology of thin porphyrin films on graphite and the effects of Zn-Phthalocyanine (Zn-Pc) adsorption on the electronic properties of graphene. It was found that the metal atom complex of porphyrin molecules can determine the morphology, intermolecular forces and ability to create thin films on a graphite surface. Zn-Pc adsorption onto graphene shifts the position of the Dirac point with respect to Fermi level which leads to localized p- and n-type doping effects in the graphene substrate. </p><p> STM, STS and Low-Energy Electron Diffraction (LEED) measurements were carried out on iridium (Ir) modified Si(111) and Si(100) surfaces. The Ir-modified Si(111) surface exhibited a &radic;7&times;&radic;7 <i>R </i>19.1&deg; domain formation that was composed of Ir-ring clusters. LEED measurements showed that on Ir-modified Si(100), a <i>p</i>(2&times;2) structure arose after annealing at ~700&deg;C. The proposed model for the Ir-silicide nanowires shows that an Ir atom replaces every other Si dimer along the Si dimer rows of Si(100)-2&times;1.</p>

<p> This thesis reports on measurements of the switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy. The Co-Ni nanopillars are incorporated into a spin-valve device - a two terminal device consisting of two ultrathin (1-3 nm) Co-Ni ferromagnets separated by a thin (4 nm) Cu spacer patterned into ellipses and circles with lateral sizes ranging from 40-300 nm. Magnetic fields applied along the uniaxial anisotropy axis can switch the alignment of the constituent ferromagnetic layers between anti-parallel and parallel. Electric currents flowing can also switch the nanopillar through the spin-transfer torque effect - an electric current transfers spin-angular momentum from conduction electrons to the background magnetization of a ferromagnet, ultimately manifesting as a torque on the magnetization. </p><p> Lateral geometry effects were studied on nanopillars with notches along the perimeter. Switching field measurements revealed an asymmetry between the anti-parallel (AP) to parallel (P) and P to AP switching field distributions. A phenomenological model that considers the spatially inhomogeneous dipole field from the polarizing layer explains this asymmetry. </p><p> In nanopillars with an 80 nm circular diameter, switching field measurements taken in a cryostat reveal non-uniform magnetization configurations during reversal. At the lowest temperatures (12 K), the transition between uniform states (P to AP) shows three consecutive hysteretic jumps. The thermal stability of the transition states was investigated for temperatures between 12 K and room temperature. </p><p> The thermally activated magnetization reversal model by N&eacute;el and Brown was tested on 75 nm diameter spin-valves between 20 and 400 K. The temperature dependence of the statistics of switching reflects enhanced thermal fluctuations and cannot be modeled by the N&eacute;el expression for the energy barrier. Taking into account the implicit temperature dependence of the energy barrier from the saturation magnetization and perpendicular anisotropy energy explains this discrepancy. </p><p> The effective barrier model for spin-torque thermally-activated switching of Co-Ni nanopillars was investigated. We extracted an effective energy barrier height for switching field distributions under several dc currents. The results mostly agree with the prediction that the current modifies the barrier height. However, rare switching events at the tails of the distributions reveal qualitative deviations from this model.</p>

No description available.

<p> The fractional quantum Hall effect (FQHE) is the archetype of the strongly correlated systems and the topologically ordered phases. Unlike the integer quantum Hall effect (IQHE) which can be explained by single-particle physics, FQHE exhibits many emergent properties that are due to the strong correlation among many electrons. In this Thesis, among those emergent properties of FQHE, we focus on the guiding-center metric, the guiding-center Hall viscosity, the guiding-center spin, the intrinsic electric dipole moment and the orbital entanglement spectrum. </p><p> Specifically, we show that the discontinuity of guiding-center Hall viscosity (a bulk property) at edges of incompressible quantum Hall fluids is associated with the presence of an intrinsic electric dipole moment on the edge. If there is a gradient of drift velocity due to a non-uniform electric field, the discontinuity in the induced stress is exactly balanced by the electric force on the dipole. </p><p> We show that the total Hall viscosity has two distinct contributions: a "trivial'' contribution associated with the geometry of the Landau orbits, and a non-trivial contribution associated with guiding-center correlations. </p><p> We describe a relation between the intrinsic dipole moment and "momentum polarization'', which relates the guiding-center Hall viscosity to the "orbital entanglement spectrum(OES)''. </p><p> We observe that using the computationally-more-onerous "real-space entanglement spectrum (RES)'' in the momentum polarization calculation just adds the trivial Landau-orbit contribution to the guiding-center part. This shows that all the non-trivial information is completely contained in the OES, which also exposes a fundamental topological quantity &gamma; = c&tilde; &minus; &nu;, the difference between the "chiral stress-energy anomaly'' (or signed conformal anomaly) and the chiral charge anomaly. This quantity characterizes correlated fractional quantum Hall fluids, and vanishes in integer quantum Hall fluids which are uncorrelated.</p>