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.

Thermal conductivity is a powerful tool to probe the phonon and electron exitations in a solid, especially in superconductors were one can basically tune the respective electronic and phononic contributions by applying a magnetic field below Tc. / After a short review on the concepts of superconductivity, thermal conductivity and amorphous matter, we present a study of the thermal conductivity of an exotic material, the amorphous metallic superconductor Fe0.5Ni 0.5Zr2. The results indicate an unexpected dominant electonic contribution to the thermal conductivity across the superconducting transition, in accordance with an inhomogeneous sample composed of a bulk normal phase with inhomogeneous superconducting phases.

The RMn6T6-xXx family of compounds (R = rare earth; T = Ge, Sn; X = Ga, In) has seen a lasting and intensive series of studies over the past several years. In these systems, a spin reorientation process, which is a pure rotation of the magnetic structure relative to the crystal axes, can be used to determine the anisotropic contributions to the transferred hyperfine fields at the Sn sites. The anisotropic contribution has been shown to be substantial in the MnSn2 and FeSn2 compounds, and is an important fraction of the overall transferred hyperfine field. A spin reorientation transition can be either temperature-induced, or field-induced (spin-flop). The temperature-induced spin reorientation generally results from a competition between the magnetocrystalline anisotropies of the rare earth and Mn sublattices. The substitution of Sn with Ga strongly affects the anisotropy, shown here to decrease the spin reorientation temperature with increasing x by 255 +/- 18 K/Ga in TbMn6Sn 6-xGax. However, the sublattice anisotropies seem unaffected by In substitution, and the spin reorientation temperature is nearly constant throughout a large range of In concentration. A field-induced spin-flop can be achieved by applying a large enough field perpendicular to the direction of the moments. / In this study, we show how both the temperature-induced SR and field-induced SF allow for the anisotropic field to be isolated from the isotropic contribution. The consistency between the two measurements of the anisotropic field indicates that the magnitude of the anisotropic contribution is independent of the driving force of the reorientation. We show that a complete 90° spin reorientation occurs in the ErMn6Sn5.89Ga0.11 and TbMn 6Sn6-xGax compounds (0.2 ≤ x ≤ 0.8), as well as in TbMn 6Sn5.46In0.54 at room temperature for an applied field of 0.57(3) T. The site preference for Ga substitution is investigated and compared with former results. Finally, the anisotropic contribution at one of the Sn sites is shown to exceed 40% in all of the compounds investigated, and this site assignment is confirmed.

The structural and magnetic properties of Diamagnetic/Ferromagnetic: Cu/Fe multilayers, prepared by DC-magnetron sputtering, were studied as a function of Fe layer thickness tFe. Structural characterization reveals the successful growth of high-quality layered structures along the film growth direction. However, the increasing contribution of the interface roughness was visible with decreasing tFe . X-ray diffraction data indicate the dissolution of Fe atoms in fcc Cu medium due to interfacial mixing. / The magnetic transition from ferromagnetism to paramagnetism with decreasing tFe was confirmed by conversion-electron Mossbauer spectroscopy (CEMS), vibrating sample magnetometry, and magnetotransport measurements. The monotonic decrease in the average hyperfine field with t Fe indicates that the transition is a gradual process as t Fe decreases from 34 A down to 7 A. The isomer shift of the singlets in the CEM spectra suggests the presence of fcc Fe, while the observed doublet is assigned to the Cu-Fe alloy phase at the interfaces. / The variation of magnetoresistance (MR) with t Cu indicates that for a nominal t Fe of 20 A the multilayer has a well-defined superlattice structure, whereas multilayers with nominal tFe, of 5 A have a granular-alloy-like structure. AC susceptometry provided direct evidence for island formation for nominal tFe = 5 A by exhibiting the blocking characteristics of superparamagnets. The temperature-dependence of the magnetization suggests that for nominal tFe = 5 A, 75% of the Fe atoms are in the superparamagnetic bcc phase, leaving the remaining 25% in the Cu-Fe alloy and fcc Fe phases. / The observed magnetic transition is likely due to superparamagnetic relaxation rather than a structural transition from bcc Fe to fcc Fe as t Fe decreases below a critical thickness tC at which a multilayer structure becomes an island structure.

This thesis studies the diffuse x-ray scattering from rough interfaces. We review the scaling hypothesis of the height difference correlation function of rough interfaces, and the relationship between the roughness and the specular reflectivity and diffuse scattering cross-section in the distorted wave Born approximation (DWBA). We study the properties of the position sensitive detector (PSD), particularly its dark counts and noise level. The conventional setup and off-plane scan setup are compared for their advantages and disadvantages. We use a polished silicon surface to exemplify the data processing. We find that the parameters which fit the detector scan data can fit all data from the specular reflectivity, the rocking scan and the offset scan very well. The polished silicon surface is well described by an exponential form of the height-height correlation function which satisfies the scaling hypothesis.

Monte Carlo simulations used for representing dynamical physical phenomena are studied in terms of a Markov chain operator acting on the probability distrubution of the states of a given system. The most general transition rule satisfying detailed balance and leading to a canonical ensemble probability distribution is derived using this formalism. The explicit Markov chain representing the two most commonly used canonical algorithms, the Metropolis and the Glauber transition rules, is then constructed and numerically applied to the states of an Ising model. The dynamical properties of the system are studied for each algorithm. Various measures, such as time-time correlation functions, are estimated for different system sizes and finite-size sealing is applied. In particular, the effects of the transition rule on the dynamic critical exponent is investigated. / We at first examine one- and two-dimensional systems using periodic boundary conditions. Systems with free boundary conditions were also studied, and their results were equivalent with respect to the dynamical critical properties of the system. The effects of conservation laws were also investigated and both conserved and non-conserved systems were studied. Both local and non-local spin-exchange dynamics were investigated for conserved systems. Finally, our approach was used to simulate quenches on small systems. / This method is them used to analyze phenomenological transformations done by dynamical renormalization-group (RG) methods. It is found that, when the RG transformation is linear in probability space, there exists a corresponding Markov chain generating the time sequence of the renormalized systems. An example is given for the one-dimensional Ising model.

We study the dynamics of two reaction-diffusion phenomena driven by chemical activation and thermal dissipation and evolving, respectively, on a randomly distributed or continuous medium. The first system describes the process of slow combustion of a randomly distributed reactant. It is studied by a phase-field model built up from first principles and describes the evolution of thermal and reactant concentration fields. Our combustion model incorporates thermal diffusion, activation and dissipation. We examine it in a manner which makes a connection between the propagation of combustion fronts, their kinetic roughening and the percolation transition. In so doing, we examine slow combustion in the context phase transitions. The second system describes propagation of reaction fronts arising in transformations obeying the Arrhenius law of chemical reactions. It too is modelled by a set of phase-field equations describing the dynamics of both thermal and concentration fields. A typical example of this transformation is the crystallization of an amorphous material. In addition to the features of our combustion model, this model also incorporated a realistic treatment of mass diffusion. Front propagation of our model is shown to undergo period doubling bifurcations as one varies the background temperature at which the system is maintained. The signature of these bifurcations is the same as those of the logistics map. We study how the bifurcation structure changes as a function mass diffusion, focusing on changes of the background temperature for which period doubling first emerges. This temperature is the most easily obtained experimentally.