Table of contents

A theory is presented to describe the wetting phenomena and the contact line depinning as a function of the microstructure of rough surfaces. The noise and fluctuations of the quenched disorder on self-affine rough surfaces play a important role in the analysis of the spreading of liquids on non-planar substrates. By using the long-range noise correlation function, functional relationships that show the influence of surface roughness on the contact angle, the critical surface tension and the depinning of the contact line are derived. Roughness enhances wetting and broadens the three-phase contact line.

We discuss the emergence of an orthogonality catastrophe in the response of a composite fermion liquid as the filling factor approaches , where m = 1, 2, 3... . A tunnelling experiment is proposed in which dramatic changes in the I - V characteristic should be observable as is varied. Explicit I - V characteristics calculated within the so-called modified random phase approximation, are provided for .

The broadband yellow luminescence frequently observed in GaN is shown to be consistent with transitions to a single level strongly affected by Franck - Condon effects. A level 0.6 eV above the valence band with an associated Huang - Rhys factor of 6.5 determined by the electron - phonon polar interaction fully describes the breadth of the observer band.

The observation of the electron spin resonance hyperfine (hf) spectra associated with the unpaired electron of the interface defect in thermal shows that the dominant interaction arises from a single isotope. The hf tensor displays weakly monoclinic I (nearly axial) symmetry, with the principal axes of the g and hf tensors coinciding. A molecular orbital analysis indicates that the unpaired electron resides for in a single unpaired Si hybrid orbital, found to be 14% s-like and 86% p-like, with the p-orbital markedly pointing closely along a direction at with the [100] interface normal. With oxygen not constituting an immediate part of the defect, the results firmly establish the key part of the defect as a tilted ( about ) unit.

A quasi one-dimensional model of spin transport in heterogeneous media based on the Boltzmann equation is presented in order to define the basic properties characterizing perpendicular spin transport in nanostructures. Experimental results are reviewed, first on the giant magnetoresistance of magnetic multilayers: spin dependent scattering in bulk and at interfaces, spin-diffusion length in the ferromagnetic layers and in the non-magnetic spacers. The observations of magnetoresistance associated with spin-scattering at Bloch walls are summarized. The junction magnetoresistance of ferromagnetic-insulator-ferromagnetic structures are reviewed, including the tunnel junctions produced with materials which present colossal magnetoresistance. An outlook on possible devices and novel structures is given.

Transmission of acoustic waves in two-dimensional binary solid/solid composite media composed of arrays of Duralumin cylindrical inclusions embedded in an epoxy resin matrix is studied. The experimental transmission spectrum and theoretical band structure of two periodic arrays of cylinders organized on a square lattice and on a centred rectangular network are reported. Absolute gaps extending throughout the first two-dimensional Brillouin zone are predicted. The measured transmission is observed to drop to noise level throughout frequency intervals in reasonable agreement with the calculated forbidden frequency bands.

Triple-crystal x-ray diffractometry and x-ray reflectometry have been used to determine defects in epi-ready wafers caused by mechanical treatment. Reciprocal space maps around the 400 lattice point were separately made for mechanically polished wafers before and after etching treatment. The lattice imperfections have been studied by measuring the diffusion scattering. The surface morphology has been controlled by means of x-ray reflectometry. It was shown that measurements of diffuse scattering could be made with good sensitivity in a reasonable time when there was a moderate difference between the d spacing of the sample and the monochromator.

Effects of the increase of the translational period of the VRu crystal structure on the density of states (DOS) at the Fermi level are investigated by means of first-principles band structure calculations (LMTO-ASA method) by using different types of model structure. The results reveal that the DOS of equiatomic VRu at the Fermi level is very sensitive to the changes in the translational symmetry of the crystal. Moreover, our calculations show that the increase of the translational period of the crystal structure is one reason for the considerable reduction of the DOS at the Fermi level giving one possible explanation for the observed drastic changes in physical quantities related to the DOS at the Fermi level. We have also investigated the effect of the observed crystal modulation parallel to the (100) plane of the normal tetragonal structure of VRu.

We observe a crossover in the temperature dependence of the variable-range-hopping resistivity in a three-dimensional nickel-silicon film from the Mott -behaviour to the soft-gap -behaviour with . We propose general expressions for describing such crossovers from -behaviour to -behaviour for any from 1/4 to 1. The theoretical expressions fit the experimental data well.

The momentum and energy relaxation rates associated with electron-acoustic phonon interaction in a free-standing rectangular GaAs quantum wire have been calculated taking into account confined and interface phonon modes. Phonon confinement has two major consequences: (i) it increases relaxation rates by several orders of magnitude, and (ii) it increases the ratio of absorption to emission processes in narrow intervals of energy thereby making the energy relaxation rate in these intervals negative. An external magnetic field always decreases the momentum relaxation rate (thus increasing the carrier mobility) even though the scattering rate (the inverse of the quasi-particle lifetime) may increase or decrease depending on whether the interaction is polar (piezoelectric) or non-polar (deformation potential).

In this paper, I present a detailed theoretical study of electron-photon-phonon interactions in three-dimensional electron gases (3DEGs) subjected to linearly polarized intense electromagnetic (EM) radiations. Applying the solution of the time-dependent Schrödinger equation, in which the effect of the EM radiation field is included exactly, to time-dependent perturbation theory, I have developed a novel approach for determining the probabilities of steady-state electronic transitions induced by electron-photon-phonon interactions in a 3DEG system. For the case of polar semiconductors, I have discussed the influence of the linearly polarized intense laser radiation on the electronic scattering rate for electron interactions with the radiation field and with the LO phonons. These results are pertinent to the application of recently developed terahertz or far-infrared laser sources such as free-electron lasers.

The knowledge of the temperature dependence of the thermal conductivity is necessary in many aspects. It is required, for example, as an important input parameter for the calculation of temperature distributions in metals after interaction with laser pulses. Although extensive compilations exist on this subject they may be of limited value because the data were obtained under steady state conditions where the electrons and phonons are described by a single common temperature. At short laser pulses, however, the electron and phonon subsystems are not in local thermal equilibrium and have to be characterized by different temperatures. It is shown that the validity of the often used linear dependence of the thermal conductivity on the electron temperature is limited to some few thousand kelvin and becomes definitely wrong at higher temperatures. A formula including the thermoelectric effects is derived that is valid throughout the whole temperature range as well as for the case of local thermal equilibrium and nonequilibrium.

The complex structure of a spin-glass state space can be simplified by a coarse-graining procedure, i.e. microscopic states being assembled into larger clusters. An algorithm for the coarse graining of the state space of a short-range Ising spin glass is provided, which is the basis of a coarse-grained dynamics. Different ways for modelling the transition rates in the coarse-grained state space are discussed. A comparison with the dynamics of the microscopic system shows that the dynamics in the coarse-grained state space gives an appropriate approximation.

The crystal structure of the parent alloy of the series under investigation has four distinct iron sites. Mössbauer spectra of the series with recorded at 293 and 4.2 K and fitted with four components show little site preference for Mn substitution up to x = 0.15. At x = 0.20 evidence for site preference is observed. The magnetic phases at 4.2 K were deduced from changes in the Mössbauer spectra in applied fields. The alloy with x = 0.20 is found to be ferromagnetic. Alloys with x = 0.05, 0.10 and 0.15 show evidence of a canted spin phase. A transition from a canted to a ferromagnetic phase is observed at applied fields T for the x = 0.15 alloy. Phase diagrams constructed from Mössbauer and magnetization results are compared with the predictions of a generalized theoretical model which incorporates ferromagnetic and antiferromagnetic interactions.

The temperature dependence of complete infrared reflection spectra of a betaine phosphite single crystal is reported for the polarizations parallel to a and b axes in the wavenumber range from 10 to . They are compared with previous data that were limited to the range . They are also compared with reflectivity spectra of betaine phosphate, betaine arsenate, deuterated betaine phosphite single crystals and betaine compressed powder. These comparisons allow a mode assignment. Spectra were fitted with the factorized form of the dielectric function. The role of phonons in the behaviour of the dielectric constant in the vicinity of the ferroelectric (FE)-paraelectric (PE) phase transition is discussed. The decrease of effective charges along the FE axis below the FE-PE phase transition is assigned to an increase of oxygen-hydrogen electronic orbital hybridization related to the change of average bond-length.

Infra-red (IR) absorption results on irradiated and annealed synthetic diamond are presented which confirm an earlier proposal that a component found in the defect-induced one-phonon region of some diamonds arises from positively charged single-substitutional nitrogen . The concentration ratio of to neutral substitutional nitrogen centres may be changed by shining light of various energies onto the examined samples. By correlating changes in absorption of the IR component associated with centres with changes in the component, and using a previously determined relation between the concentration of centres and peak absorption coefficient at 1130 , the relationship between peak absorption at 1332 and concentration of centres has been derived, namely 1 of absorption is produced by ppm centres. Other defects may also give rise to absorption at 1332 , but the component is uniquely identified by further peaks at 1046 and 950 .

The significance of this component is demonstrated by the fact that some samples can contain in excess of 80 ppm centres, and this must consequently be accounted for when assaying the total nitrogen concentration in such samples.

Using the above relationship useful parameters relating the concentration of neutral vacancies, negative vacancies and negatively charged nitrogen-vacancy centres to their respective zero-phonon line integrated absorptions have been derived.

The blue europium band in alkali-earth fluorophosphates, determining the allowed electric-dipole transitions in the ion, is studied. The simultaneous doping with provides a possibility of the realization of transitions and of formation of ions as blue emission centres of high intensity. The position is assumed for the ions in the apatite structure of the matrix.