A phenomenological theory of magneto-optic Kerr effect (MOKE) is presented to illustrate the connection between the magnetization and the polarization of light reflection in an isotropic medium. An apparatus measuring the MOKE of magnetic medium was designed and constructed. The surface magneto-optic Kerr effect (SMOKE) of a magnetic multilayer is a measurement of the average magnetization of several layers within the penetration depth of the light. / SMOKE measurements on a series of sputtered $ rm Ni sb{80}Co sb{20}15 A$/CU$(t sb{Cu}),$ where $t sb{Cu}$ is the thickness of Cu spacer layer, multilayers confirms that the coupling strength in these multilayers oscillates from antiferromagnetic (AF) coupling to ferromagnetic coupling as a function of Cu spacer layer thickness. Low-angle x-ray diffraction and SMOKE measurements on a series of AF-coupled $ rm (Ni sb{80}Co sb{20}15 A$/Cu20A) $ times$ N multilayers with bilayer numbers N ranging from 8 to 100 shows that cumulative interface roughness increases with increasing N, as do the saturation field and coercivity. This is possibly due to the out-of-plane anisotropy associated with cumulative interface roughness in multilayers. / An AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A) $ times$ 10 was continually annealed up to 400$ sp circ$C in several steps, and the magnetic behaviour of the sample was evaluated as a function of annealing temperatures. $ rm (Ni sb{70}Co sb{30}15 A$/CU20A/Ni$ rm sb{70}Co sb{30} A$/CU20A) $ times$ 5 multilayer was used for investigating the AF coupling between magnetic layers of unequal thicknesses. Finally, an AF-coupled $ rm (Ni sb{70}Co sb{30}15 A$/Cu20A/Ni$ rm sb{70}Co sb{30}15 A$/Cu35A) $ times$ 5 multilayer was sputtered and used to study the magnetization of an AF-coupled multilayer with two different coupling strengthes.

The Ca$ sb{x}$K$ sb{1-x}$(NO$ sb3) sb{1+x}$ glass system has been studied by means of X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The structure of the glass system was studied in XRD experiments and from the Radial Distribution Function (RDF). A structural model for this glass system was suggested with the agreement between the RDF calculation and structure model geometric calculation. DSC studies ranged from glass transition and crystallization to melting. The activation energy for crystallization was obtained. / The difficulty of handling the glass in open air was overcome by using vacuum tube to melt the sample and glove box with Ar gas to handle the glass. It is found that the handling of the samples, i.e. avoiding exposure to moisture is critical to maintaining sample quality. / For the structural studies, glasses of $ rm Ca sb{0.4}Na sb{0.6}(NO sb3) sb{1.4}, Ca sb{0.4}Rb sb{0.6}(NO sb3) sb{1.4}$ and $ rm Mg sb{0.4}K sb{0.6}(NO sb3) sb{1.4}$ were also prepared for comparison with the $ rm Ca sb{x}K sb{1-x}(NO sb3) sb{1+x}$ glasses. The same structural model applied to all of them with similar agreement. / For the DSC studies, only the $ rm Ca sb{x}K sb{1-x}(NO sb3) sb{1+x}$ glasses were used. The relation between increase of glass transition temperature $T sb{g}$ and that of divalent cation concentration is linear. It was observed that unlike the metallic glass system, the crystallization activation energies do not change with the glass composition. We also observed the irreversible relaxation effect in this glass system and the effect of supercooling in the DSC to form the glass.

We study the behavior of a simple cubic crystal interface through the analysis and simulation of the Ising model in three dimensions; we use an algorithm which permits local temperature variations by emulating thermal diffusion. We derive a description of the interface based on the thermal fluctuation population at equilibrium and then use it to identify the equilibrium and dynamic roughening transitions observed under a variety of circumstances including a planar interface at equilibrium, a metastable bulk inclusion, an evaporating inclusion and a planar interface in the presence of a driving force. We also study strongly driven interfaces which exhibit an instability and pattern formation behaviour known as the Mullins-Sekerka instability. We use a special two-dimensional version of the simulation model to examine the linear growth of unstable modes of a driven interface; we compare our simulation data to theoretical predictions for the cases of an unstable flat interface and circular disk interface. Returning to the fully three-dimensional code, we present simulation data of late-time dendrites growth, including an analysis of the information available in the thermal fields. We also show that, at low temperatures, the tips of dendrites are facetted and demonstrate a response to the driving force which is consistent with the dynamic roughening transition.

Order-disorder transitions have been studied for many years. The great number of experiments done on binary alloys makes condensed matter physics very appealing since it allows theory and experiment to progress side by side. / Using field theoretic methods, we study many aspects of physical systems such as binary alloys, which are taken out of thermodynamic equilibrium. In the introduction, an expose of basic notions is given. In the second chapter, we review an analytical method describing phase separation processes resulting from a critical quench. Physically, the latter phenomena could represent an initially disordered binary alloy, in which, following a drop in temperature, the atoms spontaneously order into a crystalline lattice. We will then study the effect a conserved field has on the kinetics of phase separation. This conserved field represents the local concentration of atoms of the alloy. In Chapter 4, we describe a theory formulated to explain some non-trivial relaxation of the structure factor seen experimentally for an initially ordered system suddenly cooled. Finally, we propose a theoretical model describing polymorphous crystallization. The model is studied via computer simulations. The results so obtained are compared to the experiment.

No description available.

No description available.

This thesis presents for the first time direct structural measurements of both reversible and irreversible structural relaxation and the glass transition in the metal-metalloid glass Pd$ sb{40}$Ni$ sb{40}$P$ sb{20}$. The techniques have been x-ray diffraction and Mossbauer spectroscopy, and a new analysis method for changes of amorphous diffraction patterns was developed. / It is found that irreversible relaxation proceeds by many local shear-type motions involving the metal atoms, and that it is accompanied by a small densification. Reversible relaxation at high annealing temperatures entails the same microscopic processes, but it does not change the density of the glass. The type of atomic processes changes continuously as the annealing temperature is lowered, and at sufficiently low temperatures the distribution of metal atoms remains constant, so that reversible relaxation then proceeds via rearrangement of the metalloid atoms. This rearrangement leads to more ordered, but less isotropic atomic sites. / The second part of the thesis is concerned with the motion of the atoms in a metallic glass below and above the glass transition. Mossbauer spectroscopy allows the direct measurement of vibrational and diffusional motion. The increase of the amplitude of atomic vibration has the same temperature dependence as the increase in volume that marks the glass transition, thus the two processes are governed by the same mechanism. The directly measured diffusional motion is in agreement with macroscopic measurements of diffusion.

The purpose of this project is to develop an algorithm that speeds up large scale simulations of many-body systems. A numerical method is implemented that simulates non-equilibrium phenomena on a mesoscopic time scale. A system is perturbed by an external force, and time averages of variables renormalized in space are calculated numerically, using results of linear response theory, as the system relaxes to equilibrium. The coarse-grained variables evolve slowly in time, allowing one to advance them on a mesoscopic time scale. / The algorithm was tested on two physical systems: a lattice confined ferromagnetic Ising model and an off-lattice Argon-like molecular system. The method simulated accurately the non-equilibrium phenomena studied. It was found that the algorithm is most efficient when it is applied to a process occurring on at least two time scales. This allows one to integrate out the fast, microscopic time scale in order to study long-time, macroscopic behaviour. Through the study of diffusion in a molecular system, it was concluded that the proposed method is computationally faster than solving the microscopic equations of motion and more accurate than solving the macroscopic equations.

X-ray Intensity Fluctuation Spectroscopy (XIFS) is an ideal technique to perform measurements on the dynamics of fluctuations in condensed matter systems. Over the past few years, XIFS has been used in several studies of dynamics in both hard condensed matter and soft condensed matter equilibrium systems. Its extension to study the dynamics of non-equilibrium systems is currently under way. In this thesis, we present the first applications of XIFS to study dynamics during a first order phase transition with nonconserved order parameter (model A). The order-disorder phase transition in the binary alloy Cu3Au has been chosen as a case study for such a non-equilibrium process and has been studied using XIFS. Our experiments have confirmed the theoretical predictions for the scaling laws describing the evolution of the density-density correlation functions, which are measured by the autocorrelation function of the scattered intensity. The covariance of the scattered intensity was found to be proportional with scaling functions with natural variables delta t = |t1 - t 2| and t¯ = t1+t22 , as predicted by theory. However, some significant early-time deviations from this scaling picture have been observed and are currently under investigations. / In order to study non-equilibrium processes in condensed matter systems, a very precise and fast temperature control system is often required. In order to trigger the particular process under study and to obtain meaningful experimental data, the temperature has to change by hundreds of degrees in very short times, while completely avoiding any over/under shooting. To achieve this, we designed and implemented a computer-controlled temperature tracking system which combines standard Proportional-Integral-Derivative (PID) feedback, thermal modeling and finite difference thermal calculations (feedforward) and Kalman filtering of the temperature readings in order to reduce the noise. The resulting Kalman-Predictive-Proportional-Integral-Derivative (KPPID) algorithm allows us to obtain accurate control, to minimize the response time and to avoid over/under shooting, even in systems with inherent noisy temperature readings and time delays. The KPPID temperature controller was successfully implemented at the Advanced Photon Source at Argonne National Laboratories and was used to perform the coherent X-ray diffraction experiments described in this thesis.

This thesis is devoted to the studies of self-assembled InAs quantum dots (QD) by low-temperature Atomic Force Microscopy (AFM) in frequency modulation mode. Several spectroscopic methods are developed to investigate single electron charging from a two-dimensional electron gas (2DEG) to an individual InAs QD. Furthermore, a new technique to measure the absolute tip-sample capacitance is also demonstrated. The main observables are the electrostatic force between the metal-coated AFM tip and sample as well as the sample-induced energy dissipation, and therefore no tunneling current has to be collected at the AFM tip. / Measurements were performed by recording simultaneously the shift in the resonant frequency and the Q-factor degradation of the oscillating cantilever either as a function of tip-sample voltage or distance. The signature of single electron charging was detected as an abrupt change in the frequency shift as well as corresponding peaks in the dissipation. The main experimental features in the force agree well with the semi-classical theory of Coulomb blockade by considering the free energy of the system. The observed dissipation peaks can be understood as a back-action effect on the oscillating cantilever beam due to the fluctuation in time of electrons tunneling back and forth between the 2DEG and the QD. / It was also possible to extract the absolute value of the tip-sample capacitance, as a consequence of the spectroscopic analysis of the electrostic force as a function of tip-sample distance for different values of the applied voltage. At the same time, the contact potential difference and the residual non-capacitive force could also be determined as a function of tip-sample distance.