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Dopant impurity migration paths and activation energies for self-interstitial-assisted migrations have been investigated based on first-principles and critical-path calculations. The calculated results reveal that B migration pathways have several choices. The present migration mechanisms suggest that B diffusion by the interstitially mechanism can show a small pre-exponential factor, while dopant impurities migrating by interstitial mechanisms can show large pre-exponential factors, corresponding to reported experimental results.

We consider a quantum many-body problem in one dimension described by a Jastrow-type wavefunction, characterized by an exponent lambda and a parameter gamma . In the limit gamma =0 the model becomes identical to the well known 1/r² pair-potential model; gamma is shown to be related to the strength of a many-body correction to the 1/r² interaction. Exact results for the one-particle density matrix are obtained for all gamma when lambda =1, for which the 1/r² part of the interaction vanishes. We show that with increasing gamma , the Fermi-liquid state (at gamma =0) crosses over to distinct gamma -dependent non Fermi-liquid states, characterized by effective 'temperatures'.

Variational calculations are performed for the ground and first excited states of D⁰ off centre and the lowest singlet and triplet states of D^- off centre in quantum wells in a magnetic field. It is found that the off-centre effect on the binding energies increases with increasing magnetic field. The binding energy of the triplet state can be larger than that of the corresponding singlet one if the magnetic field is strong enough.

The thermoelectric power of bulk semiconductors and quantum well structures is investigated for the first time using the balance equation transport theory extended to weakly non-uniform systems. In the linear transport limit the thermopower expressions obtained are independent of scattering and equivalent to the results derived from the Boltzmann equation with the relaxation time approximation. Effects of carrier heating (due to a current flow or due to an applied electric field in the crossed direction) are examined, showing that thermoelectric power is very sensitively dependent on the method of heating the electrons, and can change sign at low temperatures in the case of a strong electric field bias.

We have investigated the phase diagram of the s= 1/2 J₁-J₂-J₃ chain using finite-lattice techniques. The location of the boundary between spin-liquid and dimer phases has been estimated, and the characterization of these phases via correlation functions is presented.

EPR measurements were carried out up to 423K for the series Nd₂Cu_1-xZn_xO₄ (x=0.00-0.20) and La₂Cu_1-xZn_xO⁴ (x=0.00-0.10). Despite the drastically reduced 2D antiferromagnetic spin-correlation lengths, brought about by both Zn doping and elevated measurement temperatures, no intrinsic EPR signals have been detected from these materials.

We report the fabrication by PECVD of silicon-rich erbium-doped silica films that exhibit both 1535 nm fluorescence and visible photoluminescence. Fluorescence spectra are presented along with absorption spectra that display a strong band edge in the blue, which we ascribe to the presence of Si microclusters. We are unable to observe characteristic Er³⁺ absorption bands and propose that excitation of the rare earth is via an energy transfer process from Si microclusters.

Effects of confinement of the 4.0 nm pores of Vycor glass on the alpha relaxation associated with the glass transition were investigated for three glass-forming liquids, glycerol, propylene glycol and propylene carbonate, by dielectric relaxation spectroscopy. The relaxation shifts to lower temperatures in the isochronal (constant-frequency) measurements and to higher frequencies in the isothermal measurements for the confined liquids as compared to the bulk. Confinement induces a broadening of the relaxation and a change of its shape, The results are discussed in relation to the characteristic length of the glass transition (cooperativity length).

The method of isotopic substitution in time-of-flight neutron diffraction is applied to measure the coordination environment of Cl^- in a 0.999(2) molal solution of NaCl in fully deuterated glycerol. It is shown that the glycerol molecules act as monodentate ligands to give a Cl(glycerol) complex that comprises Cl^-...D-O hydrogen bonds, which are approximately linear and of length 2.17(3) AA. The results are compared with those obtained for the solvation of Cl^- in solutions of its salts in water, methanol and ethylene glycol (EG). A reduction from approximately six (water) to four (methanol and EG) to three (glycerol) is found for the Cl^-solvation number as the solvent is changed and, for all four solvents, the Cl^-...D-O hydrogen bond is typically linear.

We present theoretical calculations for the temperature dependence of both the static and the dynamic structure of liquid lithium. Our approach is based on the neutral pseudoatom method to obtain the screening valence electron density around a Li⁺ ion as well as the effective interatomic pair potential, and on the variational modified hypernetted chain integral equation theory of liquids to obtain the liquid static structure. Then, the dynamic structure is calculated in the viscoelastic approximation. This combination results in a whole theory free of adjustable parameters. The results obtained show rather good agreement with the available simulation and experimental data.

Fourier transform infra-red (FTIR) and positron lifetime spectroscopy (PLS) techniques have been used to quantify end-gauche, double-gauche and kink conformer concentrations in a number of the higher n-alkanes over a temperature range which includes crystalline, rotator and liquid phases. These have been correlated with ortho-positronium (o-Ps) lifetimes and intensities in identically prepared samples of dodecane (C₁₂), hexadecane(C₁₆), eisosane (C₂₀), tetracosane (C₂₄), octacosane (C₂₈) and dotriacontane (C₃₂). Consideration was given to the importance of sample preparation and the presence of impurities and free oxygen in determining the correct o-Ps lifetimes in the liquid phase. It was found that o-Ps lifetimes and intensities correlate well with the appearance of conformer defects which arise when the system leaves the all-trans configuration of the crystalline phase and approaches the rotator and liquid phases. The important volume in the determination of o-Ps lifetime was found to be the defect volume per molecule, and together with the behaviour of the o-Ps intensity as a function of temperature in the liquid phase this suggests that either the positron or positronium is trapped in the conformer defects.

The chemical potential of continuously deformable chain molecules can be estimated by measuring the average Rosenbluth weight associated with the virtual insertion of a molecule. We show how to generalize the overlapping-distribution method of Bennett to histograms of Rosenbluth weights. In this way we arrive at a scheme to estimate chemical potentials of chain molecules that is a direct generalization of the Shing-Gubbins scheme for simple molecules. In particular, our overlapping-distribution method has the nice diagnostic feature that it can detect systematic sampling problems that may occur for long chains and high densities. We apply the method to the computation of the chemical potential of flexible chains of hard spheres and find that, for the systems studied, systematic sampling errors are less important than statistical errors.

The liquid caesium-oxygen system in the metallic regime has been investigated by the NMR technique. Measurements were made of the Knight shift for both ¹³³Cs and ¹⁷O nuclei, and the nuclear relaxation time, T₁, for the latter. The Knight shift for ¹³³Cs nuclei decreases almost linearly up to 25 at.% of O and further decreases with a steeper slope to the value in Cs₂O, while the shift for ¹⁷O nuclei is almost independent of the composition up to 21 at.%. The analysis of T₁ suggests that the gradient of the electrostatic field coupled with the nuclear quadrupole moment of ¹⁷O is also insensitive to the composition. The results are discussed with particular reference to the state of the O atoms and possible ionic association in the liquid Cs-O system in the metallic regime.

A single-crystal elastic neutron scattering experiment between 4.2 and 115 K has been performed on the low-temperature monoclinic zeta phase of the layered perovskite bis(propylammonium)manganesetetrachloride (PAMC). The crystalline structure is commensurately modulated, with a modulation vector of 1/3b*, and below 39 K PAMC is an antiferromagnet with a small ferromagnetic component. The temperature dependence of the monoclinic angle ( alpha depends on the mosaicity of the crystal which increases with the number of 'cooling cycles'. The satellite reflections do not have any contribution from the magnetic ordering, but their intensity has abrupt changes that coincide with changes in either the nuclear or the magnetic ordering parameter. Magnetoelastic effects seem to influence the ordering of the crystal.

The stabilities of solitons, polarons and bipolarons in divalent-doped transpolyacetylene have been studied by considering the impurity Coulomb confinement as well as the electron-electron interactions in the framework of the tight-binding Peierls-Hubbard model. It was found that transitions between bipolarons and solitons and between bipolarons and polarons will take place under certain conditions. The calculated values of the energy transitions agree well with the experimental results in the dilute Ca²⁺-doped trans-polyacetylene material. The stability of excitations with respect to the impurity confinement and the electron-electron interactions have been discussed.

The problem of thermal conduction in a perturbed one-dimensional Toda lattice is investigated within the framework of non-equilibrium thermodynamics. The intrinsic thermal resistance of the lattice is due to its anharmonicity with the dominant contributing mechanism involving soliton-phonon interactions. Our calculations indicate that the coefficient of heat conduction is exceedingly small at both very low and very high temperatures and exhibits an expected maximum in the intermediate temperature range.

The rate of absorption of phonons from a monochromatic beam by a 2D electron system in a strong magnetic field is calculated in the diffusive regime and it is seen that, for certain phonon frequencies, the variation of absorption with Fermi energy should have two maxima per Landau level with a separation which scales as B. This calculation is extended into the lower-temperature, quantum Hall regime using a scaling expression for the diffusion constant showing that the phonon absorption should vanish as the temperature is lowered in the same manner as the longitudinal conductivity.

The energy of an atom as a function of its coordination number has been calculated within the tight-binding model for added vacancies in FCC and BCC lattices considering s and d orbitals. We show that the dispersion due to the different possible topologies of nearest-neighbour vacancies is larger when d bands are replaced by five degenerate s bands in simplified models. We also show that when calculations are performed going beyond the second moment the cohesive band energy follows approximately a square-root dependence with coordination for s bands but that for d bands it has a different dependence. Besides the case of a bulk atom with different numbers of nearest-neighbour vacancies, the cases of surfaces and lattices containing uniformly distributed vacancies have also been considered.

The influence of far infra-red (FIR) radiation on the tunnel current of GaAs/GaAlAs double-barrier resonant tunnelling structures is investigated both experimentally and theoretically. For a tunnelling process characterized by a transmission coefficient with a full width at half maximum Gamma _c which is smaller than the photon energy h(cross) omega , a theoretical FIR response which depends on the radiation energy is obtained while, for a tunnelling process with Gamma _c larger than h(cross) omega , this energy dependence is not observed. Although a clear dependence on the radiation energy could not be observed experimentally we show that a classical rectification cannot explain the obtained FIR response.

A single crystal of the solid-state-laser material Mn⁵⁺-doped Sr₅(PO₄)₃Cl, wherein the Mn⁵⁺ ion substitutes for the tetrahedrally coordinated P⁵⁺ ion, has been investigated by X-band (9.6 GHz) EPR at 296, 190 and 120 K. The fine- and hyperfine-structure spin-Hamiltonian parameters have been estimated rigorously from a simultaneous fitting of the EPR line positions observed for several orientations of the external magnetic field in the various magnetic planes. The increase in EPR linewidths suggests enhanced vibrations of MnO₄^3- tetrahedra, and/or strain effects, with increasing temperature.

Symmetry adapted expressions for the magnetic and quadrupolar nuclear spin-lattice relaxation time T₁ in HCP metals are derived from Dirac theory. They are applied systematically to 3d, 4d and 5d metals (Sc, Ti, Y, Zr, Tc, Lu, Hf, Re, Os) on the basis of semi-relativistic and full-relativistic self-consistent LMTO calculations. General trends and relativistic effects are discussed. The relaxation rate T^-1₁ in Zr is overestimated theoretically by a factor of two, as already found by Asada and Terakura. There is strong evidence that the reason for this error lies in spin-orbit splitting. Shifts of 3 mRy in the band position explain the experimental T^-1₁ in Zr. The Fermi surface of Ti is discussed in connection with the theoretical relaxation rate. Some quantities that are useful for the evaluation of measurements like hyperfine coupling constants and ratios between magnetic and quadrupole relaxation rates are presented. Comparison with the experimental data shows that the quadrupole scattering is well reproduced by the theory.

Similar to our earlier observations of site-dependent photoluminescence of Cu⁺ ions in a silica glass a phenomenon of site-sensitive copper(I)-related thermoluminescence has been observed in the glass after gamma -irradiation. The results have been interpreted in terms of a process of site-to-site direct recombination of different copper-associated aluminium hole centres with their respective electrons.

The X-ray emission lines S K beta (3p to 1s) and S L_2,3 (3s to 2p) have been measured for the misfit layer compounds (BiS)_1.08NbS₂ and (PbS)_1.14TaS₂ and the corresponding binary sulphides Bi₂S₃, NbS₂, PbS and TaS₂. The X-ray emission data are compared with X-ray photoelectron spectra and band structure calculations of isolated model layers. The experimental data show very clearly the character of the different valence band states, and partial density of states schemes are easily deduced from these data. A comparison with band structure calculations shows a good agreement with the measured spectra.

In the X-ray-induced luminescence band peaking at 560 nm we have detected the electron paramagnetic resonance (EPR) spectrum using optical detection (ODEPR) Of V_K centres, which have their molecular axes perpendicular to the magnetic field, an EPR was only detected as a microwave-induced change in the magnetic circular polarization of the emission, and not as an emission intensity change. No parallel centres were seen, nor any trapped electron centre. The observations are explained as a recombination luminescence of a kind of Tl-bound exciton. Furthermore, the ODEPR via the magnetic circular dichroism of the absorption of V_KA centres generated by X-irradiation at 4.2 K and trapped near Tl⁺ and near Na⁺ were measured. These centres are room-temperature stable for a few minutes and responsible for afterglow effects when using CsI:Tl, Na as X-ray-scintillator crystals.

Interband optical transitions in a semiconductor superlattice induced by an intense optical wave in the presence of uniform electric and magnetic fields are analysed. Both the oscillating electric field of the optical wave and the uniform magnetic field are directed perpendicular to the heterolayers whilst the uniform electric field is in a direction parallel to the heterolayers. The superlattice potential is modelled by a periodic chain of delta -function-type barriers. Quasi-energetic time-dependent states are used. The explicit dependence of the coefficient of the multiphoton absorption on the frequency and magnitude of the light wave, the superlattice parameters and the magnitudes of the uniform fields is obtained. It is shown that the dynamical Stark effect induced by the strong oscillating electric field leads to a shift of the edge of absorption to shorter wavelengths. The form of magneto-absorption essentially depends upon the parity of the number of absorbed photons and the relationship between the separation of the Landau levels and the total width of the electron and hole minibands. It is found that the main effect of a uniform electric field is to shift the absorption edge to longer wavelengths (the Franz-Keldysh effect).