Table of contents

A novel approach which enables one to treat the strong-coupling regime of the KPZ equation is proposed. The essence of the method consists in understanding the reason for the increase of the effective coupling constant under renormalization and incorporating this information into the renormalization group (RG) procedure. By using this generalized RG method I computed the critical exponents at the strong-coupling fixed point of the KPZ equation for space dimensions 2<or=d<or=4: the roughness exponent zeta =(4-d)/4 and the dynamic exponent z=(4+d)/4.

Surface plasmon dispersion on Pd(110) was investigated along the high-symmetry directions (110) and (001) with angle-resolved electron-energy-loss spectroscopy. A large negative initial dispersion with transferred momentum is found in spite of the strong shift of plasmon and surface plasmon frequencies induced by the presence of the d bands. Their unfilled character in transition metals is thus demonstrated to affect the dispersion of the surface plasmon in a very different way than for noble metals, where the filled d bands are responsible for the positive initial dispersion.

In this letter we study the dielectric properties of brine-impregnated artificial sandstones. The frequency-dependent dielectric permittivity shows a relaxation due to the electrochemical double layer at the interfaces. Good agreement was obtained with a theoretical expression, rigorously valid for dilute colloidal suspensions. The relaxation frequency and amplitude displayed clear dependences on brine conductivity. At the highest liquid conductivities studied, electrode effects were observed at low frequencies.

This work presents the theoretical study of the controlled lateral translation of an Xe atom physisorbed on the Ni(110) surface. The motion of the Xe is manipulated by the tip of the scanning tunnelling microscope. The interaction of the physisorbed atom with the tip and sample surface is described by empirical potentials. Using molecular statics and dynamics, the energetics and different modes of the translation are revealed. Important effects of electrode relaxation, tip geometry and material parameters are briefly discussed.

We discuss the giant magnetoresistance (GMR) in magnetic superlattices with an s-d scattering model on the assumption that d states are bound in magnetic layers. The GMR is calculated by using the quantum Boltzmann equation using Kronig-Penney-type potentials. Spin-dependent interfacial scattering depends on the number of scatterers, the height of the scattering potentials and the amplitude of the wave function of the d state at interfaces, while spin-dependent bulk scattering is attributed to the spin-dependent density of states (DOS) of d states. Our model agrees well with the measured GMR in Co/Cu superlattices with artificially mixed interfaces, when we assume that the minority-spin d states are strongly bound in Co layers. Therefore, the spin-dependent scattering in Co/Cu superlattices is attributed to the spin-dependent DOS of the d states in the Co layers.

We have measured the infrared-optical properties of ceramic beryllium oxide and observed a pronounced reflectance minimum in the reststrahlen band. This feature can be due to phonon absorption in voids in the material or in surface bumps and pits. Calculated reflectance spectra for each of these mechanisms show qualitative agreement with experiment and both effects are probably present in our experimental situation. A small reflectance dip corresponding to the longitudinal optical phonon mode was observed in our experiments. For a bulk sample, this mode can only be excited by bumps at the surface. This shows that phonon absorption in surface features is of great importance for the reststrahlen band in beryllium oxide.

We report pressure-dependent optical studies for different sized CdS_xSe_1-x nanocrystals embedded in a glass matrix. The increase in the phase stability in going from wurtzite to rock salt structure is reversible and size dependent. Different possible sources such as strain from defects, semiconductor-to-glass-matrix thermal expansion mismatch, increase in the electronic energy due to confinement, and surface tension which may cause this effect are discussed. Results indicate that surface tension is the major contribution and a simple model is developed that produces estimates of the size distribution and difference between the surface tensions of the two phases.

Slow-positron-beam studies on aluminium-implanted mercury cadmium telluride are presented. Single crystals were implanted with 320 keV Al ions up to 3*10¹² fluence at room temperature and 1*10¹⁴ ions cm^-2 fluence at 100 K and 300 K. We discuss the effect of the native oxide layer on the positron spectra and show that the oxide-crystal interface acts as a strong positron trap. By using both the core (W) and the valence (S) annihilation fractions we can separate oxide-related positron effects at the surface from the damage in the crystal. Implantation introduces small vacancy clusters. On the basis of the relative Doppler parameters of the defects created (S_d/S_b=1.05, W_d/W_b=0 80), they are most probably divacancies. The divacancy profile is found to extend from the surface to a depth comparable to the mean Al implantation depth. At room temperature divacancy creation reaches saturation at 3*10¹² ions cm^-2 fluence with an estimated divacancy concentration of 4*10¹⁶ cm^-3. After implantation at low temperature (100 K) and annealing at 360 K the divacancy creation exceeds 10¹⁸ cm^-3.

Measurements are reported of the low-energy electron emission spectrum from a solid titanium target bombarded with Ar and Kr ions with energies in the range 2 keV to 5 keV. The ion-induced electron spectrum shows considerable structure which is not present in electron-beam-excited spectra. The ion-induced spectrum is interpreted as arising from atoms sputtered free of the surface in excited states. However, comparison with the free-atom electron spectrum shows both similarities and significant differences. Possible excitation processes are discussed and tentative labels assigned to the observed peaks.

X-ray diffraction and Raman spectroscopy studies of alpha -PbO and (PbO)_1-x(TiO₂)_x were performed over a wide temperature range. Investigations on both samples allow us to point out useful information concerning lone-pair interactions from both structural and dynamical points of view. The complementarity of the experimental data gives a better understanding of the phase transition process in PbO, and also of the stability of the tetragonal structure in the solid solution (PbO)_1-x(TiO₂)x.

Molecular dynamics simulations are performed for a ZrF₄-BaF₂ glass system, which is expected to be a good ion-conducting material, in order to investigate the fundamental conduction dynamics of fluoride ions in the glass. The simulation results show that the ionic conduction is governed by the hopping motion of fluoride ions, with an average hopping distance of 2.5 AA, in the glass. This is clearly different from the diffusive motion observed in the melt. It is also found that the mobility is clearly different between bridging (Zr-F-Zr) and non-bridging (Zr-F-(Ba), (Ba)-F-(Ba)) fluoride ions in both glass and melt. The present result gives a satisfactory explanation of two distinct time scales observed in a previous NMR measurement (Y. Kawamoto and J. Fujiwara, 1990 Phys. Chem. Glasses 31 117). The first-passage-time approach is applied to the melt to determine the self-diffusion coefficients of the bridging and the non-bridging fluoride ions separately.

We present here a technique for the calculation of configurationally averaged quantities in the reciprocal k-space representation, such as the spectral function and complex band structures. We apply the technique to AgPd alloys in conjunction with the tight-binding linearized muffin-tin orbital basis. We also indicate why the same technique is ideal for application to the more accurate screened KKR and allows us to go beyond the single-site coherent potential approximation and include multi-site effects such as short-ranged ordering and local lattice distortions due to size mismatch of the constituent atoms.

We present a calculation of the self-trapping properties in alpha -quartz of aluminium-sodium centres using a Mott-Littleton calculation. It is found that the hole in (AlO₄/M)⁰ with M=Na is most energetically favourable to self-trap at an oxygen atom nearest to the Al ion with a 'short' bond. It is also found that the Na ion is in the nearby c-axis channel on the long-bond side of the Al ion. These calculated results agree well with the experimental results. We also found that the hole is also energetically favourable to self-trap at an oxygen ion next nearest to the Al ion. The hole-trapping energies in the two cases are similar and therefore their sites may not be easily distinguished in the experiment.

Linear ac transport of a one-dimensional electron gas in cylindrical GaAs quantum wires (QWs) under zero to moderate DC bias fields has been examined on the basis of the balance equation transport theory. Dynamic screening of the electron-electron interaction is considered in the random phase approximation. In contrast to the case without a DC bias field, the AC mobility contains an additional contribution from the electron temperature oscillation when a DC bias field is simultaneously applied. Numerical results at 4.2 K show that the plasma contributions noticeably change the memory functions even with a DC bias of moderate strength. As a result, the AC mobility is appreciably influenced by the plasma excitation at frequency ranging from 1 GHz to 30 GHz.

The changes of profiles along the a, b and c directions of a Bi₂Sr₂CaCu₂O_delta single crystal were examined by the X-ray diffraction method over the temperature range from 297 K to 77. Splitting of the (0k0) and (h00) diffraction peaks appeared in the temperature regions from 262 to 222 K and from 226 to 156 K, respectively. Changes of the modulation structure appear in the temperature regions from 207 to 202 K and from 112 to 102 K. Moreover, there is no remarkable change of the (00l) diffraction peaks. Below the temperature of 91 K, the (040) diffraction peak obviously begins to broaden.

We study the T=0 frustrated phase of the 1D quantum spin- 1/2 system with nearest-neighbour and next-nearest-neighbour isotropic exchange known as the Majumdar-Ghosh Hamiltonian. We first apply the coupled-cluster method of quantum many-body theory based on a spiral model state to obtain the ground-state energy and the pitch angle. These results are compared with accurate numerical results using the density matrix renormalization group method, which also gives the correlation functions. We also investigate the periodicity of the phase using the Marshall sign criterion. We discuss particularly the behaviour close to the phase transitions at each end of the frustrated phase.

Using numerical diagonalization of small systems we obtain the thermodynamics of the S= 1/2 and S=1 Haldane-Shastry (HS) model. We study the correlation functions and the susceptibility and compare them with the results for the Heisenberg (H) model. We find evidence that in the S=1 case the low-T susceptibility decays exponentially to zero, indicating the existence of a gap, in agreement with our earlier study of the ground-state properties. The correlation functions (S^z(0)S^z(m)) for the HS model decay faster than for the Heisenberg case, with both m and temperature for both values of the spin. For large T all correlation functions for the HS model become negative.

The magnetic field dependence of cyclotron resonance linewidths is examined theoretically on the basis of the projection technique. It is shown that in the quantum limit of pure Ge and Si the widths increase with the magnetic field, and the result for Ge agrees quite well with the existing experimental data.

The 195 K cubic-to-tetragonal structural phase transition (SPT) in RbCaF₃ crystals has been investigated by electron nuclear double resonance (ENDOR) using Mn²⁺ as a probe. The rotational angle of the fluorine octahedra, which is the local order parameter of the transition, has been determined at 40 K for the first and second shells of F- ions surrounding the Mn²⁺ impurities. The values obtained are 5.1 degrees +or-0.2 degrees for the first shell and 7.4 degrees +or-1 degrees for the second shell. The thermal evolution of the first shell angle at temperatures close to that of the SPT has also been studied. The results have been compared with those in RbCdF₃:Mn²⁺. The first shell angle measured at 40 K is similar to the one in RbCdF₃:Mn²⁺. The second shell angle is almost double that in RbCdF₃:Mn²⁺. Covalency effects through Cd²⁺ ions are suggested to account for this difference.

The dielectric permittivity and the dielectric losses of PbZr_1-xTi_xO₃ (x=0.03, x=0.04, x=0.05) ceramics doped with 1% Nb₂O₅ were investigated as functions of frequency and temperature. A large and unambiguous dielectric relaxation is detected at high frequency and is shown to be strongly dependent on the temperature. The minimum of the relaxation time and the maximum of the relaxation strength appear to be clearly connected with the ferroelectric-paraelectric phase transition.

We report the hard magnetic behaviour of composite magnets prepared by directly mixing micrometre Sm-Fe-N grains with micrometre iron particles and nanometre iron particles, respectively. Remanence enhancement has been found in composite magnets prepared by directly mixing the micrometre Sm-Fe-N grains with nanometre iron particles. Our experimental results indicate that for remanence enhancement to occur in composite materials the size of the soft magnetic phase involved must be nanometre, while the particle size of the hard magnetic phase involved need not be limited to nanometre scales.