At low temperature, we have used thermal conductivity as a directional probe of the residual normal fluid in two superconductors, UPd2Al 3 (a heavy fermion) and YBa2Cu3O7-delta (a high-Tc cuprate). By extrapolating our measurements to zero temperature, we can shed light on zero energy quasiparticles and the structure of the superconducting gap. / For both superconductors, we review measurements pertaining to the density of states. In the case of the heavy fermion superconductor UPd2Al 3, we have found a finite anisotropy between b axis and c axis heat conduction, which excludes those gap structures with only zeroes along c or in the equatorial plane of a spherical Fermi surface; however, our results are consistent for two line nodes equidistant from the equatorial plane, as in the A 1g gap. Comparisons to theory developed for UPt3 show qualitative agreement with two hybrid gaps with strong spin-orbit coupling, of E2u and E 1g symmetry. / For YBa2Cu3O7-delta, because the gap symmetry has been established as dx2-y2 , we can go much further as regards a quantitative analysis. The anisotropy in the thermal conductivity was measured along both high symmetry directions. A residual T-linear term in kappa(T) was observed in both directions. In the CuO2 planes (J∥ a) the magnitude of the residual normal fluid conduction is perfectly consistent with the temperature dependence of the penetration depth, within the theory for a d-wave superconductor. The value for J∥b is slightly larger, yielding an anisotropy ratio of 1.3 +/- 0.3. This is considerably weaker than that observed in the normal state resistivity, pointing to a suppressed heat conduction by quasiparticles in the chains, either due to strong defect scattering or a gapped excitation spectrum. / With the application of an external magnetic field (up to 8 T), we can study the effect of vortices on quasiparticle transport. The residual linear term increases with field, directly reflecting the occupation of extended quasiparticle states. A study for different Zn impurity concentrations reveals a good agreement with recent calculations for a d-wave gap. The magnitude of the suppression indicates that Zn impurity scattering needs to be treated in the resonant impurity scattering limit, until now an unverified assumption. Together with specific heat measurements, we obtain a quantitative measure of the gap near the nodes.

The metallic adhesion and tunneling properties of an atomically defined junction were measured and analyzed. The junction consisted of a tip opposing a flat surface in the scanning probe microscopy (SPM) configuration. Measurements were performed in ultrahigh vacuum (UHV) at 150 K. Sub-nN force resolution was achieved on a stiff cantilever beam employing an in-situ differential interferometer. Tips were prepared from W and Ir wire and imaged with atomic resolution in-situ using field ion microscopy (FIM). Ultrasharp tips with an apex radius of 20--30 A were fabricated from single crystal W(111) wire and engineered with FIM to terminate in only three atoms. Calculations indicate that for those tips metallic adhesion forces dominate over van der Waals and capacitive electrostatic forces. The sample was a thin (111) oriented Au film. Metallic adhesion forces and the tunneling current were measured simultaneously for the W-Au system as a function of tip sample separation. In contrast to theoretical simulations the system featured exceptional mechanical stability with adhesive forces of up to 5 nN. In particular no indications of a sudden jump-to-contact, which is commonly believed to be an inherent property of metallic contacts, were found. Furthermore, the range over which the metallic adhesion forces act is four times larger than expected. Experiments with sharp but not atomically defined W tips corroborate those results. The observed long interaction range is discussed in the framework of various models. Some of the consequences of this new property for force microscopy applications are pointed out.

An extensive study of a-FexTM 1-xZr2 with TM = {V, Cr, Mn, Co, Ni, Cu} was undertaken in order to gain insight into the glassy structure, the metastable "big-cube" structure of the intermediate crystallisation product, and the evolution process involved therein. The stability of the glassy state was examined by differential scanning calorimetry (DSC). Generally higher temperatures and more negative enthalpies of crystallisation were observed for the glass system where Fe was substituted with {Co, Ni, Cu} than for the system where Fe was substituted with {V, Cr, Mn}. A proposed hypothetical crystallisation mechanism involved in the evolution of the metastable cF96 state (instead of the equilibrium tI12 state) was tested. Oxygen impurities present in the amorphous state were shown to be responsible for nucleating the cF96 big cube. Upon removal of the oxygen nucleation sites through hydrogenation of the glasses, the crystallisation proceeded directly to the equilibrium tetragonal structure bypassing the metastable phase. The validity of an assumed invariant structure in late transition-early transition metal (LT-ET) binary glasses was examined by means of Mossbauer spectroscopy. Variations in isomer shift (delta) and quadrupole splitting (Delta) upon TM substitution were consistent with variations in the density of states (DOS) at the Fermi level (EF). An assumed constant structure for (4d ET)-(3d LT) glasses is indeed justified. Variations in atomic packing were followed by measuring Delta. Delta increased as the atomic number of the TM increased. For the a-Fe xCu1-xZr 2 series, a break in the concentration dependence of Delta at x ≈ 0.3 is observed which mirrors the change in crystallisation from cF96 to tI6. Furthermore, comparisons of the glassy, metastable cubic and equilibrium tetragonal Mossbauer spectral data show obvious similarities between the glass and big cube which strongly suggest the existence of a common local (short-range) order between the two

<p> Magnetic property of the symmetric Double Exchange Spring System, soft(S)/hard(H)/soft(S) ferromagnetic layers NiFe (Py)/SmFe/NiFe (Py), was investigated using Magneto Optical Kerr Effect (MOKE) measurement. Exchange spring magnet, H/S bilayer, shows a unique magnetic hysteresis curve due to the non-collinear magnetization developed by magnetic coupling of the two layers. In order to produce a symmetric non-collinearity in magnetization, the thicknesses of the two soft layers are controlled to be the same during the deposition. Due to the finite skin depth of MOKE measurement magnetic hysteresis loop for each soft layer could be measured separately by adjusting the right thickness of the layers. To measure the bottom soft layer transparent glass substrate was used for thin film deposition. We first observed an asymmetric hysteresis loop of the double exchange spring system by MOKE measurement. This is due to the existence of quadratic MOKE (QMOKE) signal caused by the in-plane magnetic anisotropy. Linear MOKE (LMOKE) and QMOKE signal were separated from the general MOKE signal using a symmetry operation. In general, the samples that have the induced easy axis have less significant QMOKE signal than those that do not have the easy axis. Second, from the LMOKE measurement, we found that the magnetic hysteresis loops for the bottom and the top S layers are not the same. The magnetic hysteresis loop from LMOKE measurements data was compared with the one measured by Alternating Gradient Magnetometer (AGM). AGM measures the total magnetization of the whole structure. Our data shows that the coercivity of the bottom S measured from LMOKE is closer to the coercivity of the first switching measured from AGM and is much smaller than that of the top S from MOKE. The coercivity of the top S from LMOKE is closer to that of the second switching from AGM. This indicates that the top S is, to some extent, strongly coupled with the hard layer causing them to switch together; while the bottom S is much less coupled so that its switching is spiral. In other words, the bottom S provides the non-collinearity as we expected from exchange spring magnets, while the top S does not. We found experimentally that within an acceptable uncertainty, the non-collinearity provided by the two soft layers is not symmetric despite the symmetry of the structure. A possible explanation of this general trend is that it is the difference in the surface roughness between the bottom Py/SmFe surface and the top Py/SmFe surface that causes the asymmetric non-collinearity, since we found that the interface between the top Py and the SmFe is rougher than the one between the bottom Py and the SmFe. Further investigation needs to be done to experimentally explain how the difference in the surface roughness affects the magnetic coupling between the soft and hard magnetic layers. </p>

The x-ray total structure factor of the glassy-metal alloys $Mg sb{70}Zn sb{30}, Ca sb{70}Mg sb{30}$ and $Mg sb{85.5}Cu sb{14.5}$ has been measured at three temperatures: 9K, 150K, and 300K. The data have a statistical precision of about.8% and an absolute accuracy of roughly 3%. / Percus-Yevick hard sphere structure factors may be fitted quite accurately to the data in the region of the first peak. In addition, the variation of the experimental structure factor with composition is found to be consistent with the Percus-Yevick theory. At low k values, Percus-Yevick and other theoretical model structure factors are in poor agreement with the data. / Within experimental error, the temperature dependence of the structure factors is in agreement with the Debye plane wave phonon model of atomic vibrations. / The measured structure factors are used to calculate the electrical resistivity from the Faber-Ziman equation. In most cases, the calculations yield both the correct magnitude of resistivity and sign of the temperature coefficient of resistivity.

The kinetics of spinodal decomposition has been studied by Monte Carlo renormalization group method. Using a standard block-spin transformation, we numerically renormalize the evolving configurations during the phase separation of a kinetic Ising model with spin-exchange dynamics. We find that in the scaling regime, the average domain size $R$($t$) grows in time as $R$ $ sim$ $t sp{n}$, with $n$ = 0.338 $ pm$ 0.008 consistent with the classical $n$ = 1/3 result of Lifshitz and Slyozov. A scaling form for the structure factor is obtained, which is invariant under the renormalization group transformation. / The fluctuations around the average domain growth in Model A and Model B are studied using Monte Carlo simulation. The fluctuations, which are non-self-averaging, were found to have multiscaling properties and exhibit 1/$f$-like properties in the scaling regime. These properties point to the existence of analogies between dynamical and random systems, which need to be further explored.

A phase-field approach describing the formation and evolution of an hexagonally patterned surface is presented. We studied a free-energy and a time-dependent Ginzburg-Landau equation for which the order parameter is non-conserved. We give a review of the scaling phenomena in general and of hexagonal systems in particular, both from theoretical and experimental points of views. A squared shaped grid of varied sizes, with periodical boundary conditions, was used for the simulations. First, we studied the evolution of surfaces themselves. Then, we considered the evolution of the structure factor's maximum amplitude, and full width at half maximum. Scaling laws as a function of system size were found for these variables. We also made a study of surface energies. We monitored the evolution of the surface energies with time, and propose a scaling law for the energies. Finally, we studied the evolution of temporal correlation functions. We propose a further scaling law for the temporal correlation functions.

This work focuses on the atomic force microscope: its hardware, modes of operation, and applications. / The construction of a x-y sample positioner, equipped with position dependent capacitive sensor, is presented. The implementation of a temperature-controlled laser for cantilever detection, via interferometry, is also discussed. / Two modes of atomic force microscopy are used. Amplitude modulation mode images are done in vacuum using Q-control to reduce the apparent Q-factor of the cantilever. Frequency modulation mode is used to obtain non-contact images and force curves above a quantum dot or gold sample. The former leads to detection of single electron charging events from a buried 2D electron gas to the surface layer of the sample. The latter was done to determine the geometric behaviour and capacitance of high-aspect ratio cantilever tips; a method for which is presented where the height, cone angle, radius of curvature and angle to the sample can be controlled.

The zero-temperature equilibrium conductance of mesoscopic devices due to single-particle resonant tunneling was first described by Landauer [1]. The Landauer formula was later extended to the multi-channel case by Fisher and Lee [2], who reduced the problem of calculating electronic transport properties to the problem of solving for the Green's function for a given system geometry. / In this work, the single-particle formalism is extended to the study of higher-order two-particle cotunneling processes by considering many-body Green's functions. The effect of attaching leads to the system is described in terms of a two-particle self-energy, whose analytical form is written in terms of a Feynman path integral over all possible tunneling processes between the leads and the device. In addition, an efficient numerical technique for the calculation of the fully dressed Green's function of a device region attached to two-particle leads is presented. / The problem of two-particle transport is then approached, and an analogy to single-particle transport on the infinite plane is drawn. It is shown that, for nonspin flip cotunneling processes, the two-particle transport result can be related to the single-particle conductance by way of a simple convolution. Finally, results for the cotunneling contribution to the conductance of double quantum dots, or charge qubits, are presented.

X-ray microdiffraction is a powerful technique to study the microstructure of materials. In this thesis we built two x-ray micro diffraction setups and demonstrated their capabilities by two case studies. In our microfocusing setup, synchrotron x-rays were focused to a micron-size spot using a Fresnel zone plate. To scan the sample, we built a 3-axis translation stage with 30 nm step size over 25 mm travel range. Our x-ray diffraction imaging (topography) setup consisted of a monochromator, a channel-cut analyzer to define the diffraction angle, and a CCD camera with 0.645 mum pixels size to record the images. In our first project, we studied the microstructure of 90° ferroelectric domains and domain walls in barium titanate (BaTiO3). We discovered a ~ 1 mum surface-like layer below the surface where domain walls angle, strain, and domains orientation deviate from the bulk values. These can be explained in terms of total energy minimization and domain-domain interaction. In our second project, we used x-ray topography to measure lattice deformations in the free and bent states of a silicon micro-cantilever used in scanning probe microscopy. We found that the cantilever was twisted by 8 mdeg with respect to the base and there were small strains in the cantilever and joint area. In the bent state, we measured 0.3 m average radius of anticlastic curvature and a maximum of 2 x 10-5 strain at the edges of the cantilever. We discuss possible causes of the twist and the non-zero strains. Our setups and the tools we developed can be used to study the microstructure of other similar systems, as well.