Table of contents

To describe accurately the electronic structures of carbon nanotubes, a semi-empirical tight-binding approach is presented in which the main intrinsic curvatures have been fully taken into account. The calculated electronic structures and band gaps are consistent with experimental measurements. Studies of the relative importance of various intrinsic curvatures show that each curvature has a contribution of varying importance to the curvature-induced band gap. Additionally, under both uniaxial and torsional strain, semiconductor–metal–semiconductor phase transitions have been observed for primary metallic carbon nanotubes. The critical stress of the transition and the gap's sensitivity with stress are dependent on both the diameter and chirality of nanotubes, which is at variance with previous predictions.

We propose a new approach to constructing gates for quantum information processing, exploiting the properties of impurities in silicon. Quantum information, embodied in electron spins bound to deep donors, is coupled via optically induced electronic excitation. Gates are manipulated by magnetic fields and optical light pulses; individual gates are addressed by exploiting spatial and spectroscopic selectivity. Such quantum gates do not rely on small energy scales for operation, so might function at or near room temperature. We show the scheme can produce the classes of gates necessary to construct a universal quantum computer.

The present review is a topical survey of the disjoining pressure in thin liquid foam and emulsion films from both the experimental and the theoretical points of view. Section 2 deals with the latest research work on experimental techniques with which the disjoining pressure Π in foam, emulsion, and pseudo-emulsion films can be measured. Although a lot of techniques are available, the question of the origin of the charges at the water/air and the water/oil interfaces of films, which are stabilized by non-ionic surfactants, has not yet been answered. We address this question in section 3, reviewing the latest relevant literature. The relevance of structural forces for the disjoining pressure is outlined in section 4, which focuses on films which are stabilized by surfactant/polyelectrolyte mixtures.

We study tagged particle dynamics in a one-component simple liquid characterized by the Lennard-Jones (LJ) interaction potential. Extended mode coupling theory is used to obtain the correlation function which feeds back on the dynamics of the self-correlations. The cooperative dynamical effects are studied by evaluating various properties of tagged particle motion as influenced by the collective dynamics. Comparison between the results obtained for particles with purely repulsive interactions like the truncated LJ potential (or the hard-sphere interaction) and that of the full LJ potential are shown. The nature of the velocity autocorrelation function and the non-Gaussian variation of the van Hove self-correlation function is specifically highlighted here. The role of static structural input in the theory is considered especially in this regard.

We present new results of structural, electro-optical and dielectric measurements, concerning the Goldstone mode rotational viscosity and the twist elastic constant in the ferroelectric chiral smectic C (SmC^∗) phase near an N^∗–SmA–SmC^∗ multicritical point. This study has been performed on the pure chiral homologue with n = 11 from the series of biphenyl alkyloxy benzoates. An Arrhenius behaviour of the Goldstone mode rotational viscosity was obtained and the activation energy was determined for this material. The characteristic parameters are also compared to those obtained for the n = 10 compound.

A previous study of the binary system, [Sb₂O₃]_x–[ZnCl₂]_1−x (Johnson et al 2003 J. Phys.: Condens. Matter15 755–64), where nominally x = 0.25, 0.50, 0.75 and 1.00, has been extended to include Sb₂O₃–PbCl₂. Information about the structure has been obtained from a combination of neutron and x-ray diffraction measurements, which were complemented by x-ray photoelectron spectroscopy. The data clearly show preferential bonding of oxygen to antimony and chlorine to zinc or lead in a single-phase glass with minimal change in the polyhedral structure with composition. The structure appears to be controlled by the need to avoid Sb–Cl–Sb links.

We investigate the freezing transition in a two-dimensional lattice model of annealed hard squares that are subject to the influence of randomly placed quenched particles of the same size. The latter model is a porous medium. By combining two recent density functional approaches we arrive at a theory for quenched–annealed lattice fluids that treats the quenched particles on the level of their one-body density distribution. We show that this approach yields thermodynamics that compare well with results from treating matrix realizations explicitly and performing subsequent averaging over the disorder. The freezing transition from a fluid to a columnar phase is found to be continuous. On increasing matrix density it shifts towards close packing and vanishes beyond a threshold matrix density.

The phase behaviour of Ar and Kr adsorbed in Vycor glass at pressures and temperatures above the bulk triple point and below the bulk critical point has been investigated. Ar is found to condense in the pores ∼2 K above the bulk transition and freeze ∼10 K below the bulk transition. In contrast the condensation transition for Kr is shifted up by 4 K and freezing shifted down by 15 K. There is a pronounced hysteresis (4–6 K) at the liquid/solid phase boundary and a lesser amount (∼2 K) at the gas/liquid boundary. We find clear differences between the pore filling and emptying processes at the gas/liquid phase boundary and evidence of pore blocking on desorption. In addition microbubbles or large gas–liquid interfaces are thought to occur when Kr condenses in the pores but this effect is absent in Ar. Finally, solid Ar in the pores melts in a more continuous way than Kr.

We present experimental results on the condensation of ⁴He atoms on the surface of liquid ⁴He. We show that there is quantum condensation with the creation of phonons and R⁺rotons in one-to-one processes as atoms go into the Bose–Einstein condensate. These phonon and R⁺roton signals can be recognized by their time of flight, their angular distribution and their dependence on the ambient temperature. Condensing atoms also create ripplons with a high probability. We derive rate equations for the growth of the ripplon density and the ripplon decay by the creation of bulk phonons. During the atom pulse a dynamic equilibrium is established. The low-energy phonons that are created by ripplon–ripplon scattering can easily be detected and distinguished from the phonons created by quantum condensation.

From measured data, estimates are made of the probabilities of creating phonons, R⁺rotons and ripplons in condensation processes as well as estimates of the quantum evaporation probabilities of phonons and rotons.

We clearly detect R⁺rotons directly with a bolometer in the liquid ⁴He and show why the signal of R⁺rotons is obscured by the low-energy phonon signal when both the source and detector are in the liquid helium. Values of the Kapitza conductance for the Zn bolometers are derived.

Starting from the Landau–Lifshitz equation, with resonant frequency f₀ = ω₀/2π, it is demonstrated that, in the case of a magnetic fluid, the measured resonant frequency, f_res is always different from f₀, except for the case of pure resonance (i.e. zero damping parameter of Landau–Lifshitz equation) where f_res = f₀. It is also shown that f_res and the corresponding maximum absorption frequency, f_max, are different, thus supporting the deductions of Scaife, who arrived at this conclusion using an alternative theoretical approach.

Furthermore, based on complex magnetic susceptibility measurements, over the frequency range 100 MHz–6 GHz, the dependence of the ratio f_max/f_res on an external polarizing magnetic field, H_pol, over the approximate range 0 and 1.3 kOe and on particle concentration has been examined for different magnetic fluid samples. It is demonstrated how the ratio f_max/f_res tends to unity both by (i) increasing the polarizing field and (ii) decreasing the particle concentration of the samples.

A systematic experimental study of polymer-induced changes of the collective structure of model hard-sphere nanocolloids in the fluid and gel states has been carried out using ultra-small-angle x-ray scattering. The focus is on small, non-adsorbing polymer depletants where a direct transition from the homogeneous fluid phase to a nonequilibrium gel state occurs with increasing polymer additions. As the polymer concentration is increased in the homogeneous fluid phase, the low angle concentration fluctuations monotonically increase, the characteristic interparticle separation decreases and tends to saturate, and the intensity of the cage order peak varies in a non-monotonic manner. These equilibrium structural changes depend in a systematic fashion on colloid volume fraction and polymer–colloid size asymmetry, and are in near quantitative agreement with the parameter-free polymer reference interaction site model theory calculations. By combining the accurate equilibrium theory with experimental observations, the loss of ergodicity and nonequilibrium structure formation in the gel state can be deduced. Abrupt departures between theory and experiment on the ∼2–3 particle diameter and greater length scales are observed as the gel boundary is traversed. The liquid-like local cage structure is arrested. Intermediate scale fluctuations are suppressed suggesting the formation of small, compact clusters. Large amplitude, Porod-like fluctuations emerge on large length scales due to quenched heterogeneities which are analysed using a random two-phase composite model. By combining the results of all the scattering experiments and theoretical calculations a qualitative real space picture of the gel microstructure is constructed, and its mechanical consequences are qualitatively discussed.

The true Fermi surface of a fermionic many-body system can be viewed as a fixed point manifold of the renormalization group (RG). Within the framework of the exact functional RG we show that the fixed point condition implies an exact integral equation for the counter-term which is needed for a self-consistent calculation of the Fermi surface. In the simplest approximation, our integral equation reduces to the self-consistent Hartree–Fock equation for the counter-term.

The temperature T and magnetic field H dependences of the electrical resistivity ρ of the recently discovered heavy-fermion superconductor PrOs₄Sb₁₂ have features that are associated with the splitting of the Pr³⁺ Hund's rule multiplet by the crystalline electric field (CEF). These features are apparently due to magnetic exchange and aspherical Coulomb scattering from the thermally populated CEF-split Pr³⁺ energy levels. The ρ(T) data in zero magnetic field can be described well by calculations based on CEF theory for various ratios of magnetic exchange and aspherical Coulomb scattering, and yield CEF parameters that are qualitatively consistent with those previously derived from magnetic susceptibility, specific heat, and inelastic neutron scattering measurements. Calculated ρ(H) isotherms for a Γ₃ ground state qualitatively account for the 'dome-shaped' feature in the measured ρ(H) isotherms.

Data available on the fd-transition energies of Ce³⁺ in inorganic compounds are compared with those of Eu²⁺ in the same compounds. Despite differing charge compensating defects, clear correlation was found. The redshift of absorption, the Stokes shift of emission, the centroid shift of the 5d configuration and the total crystal field splitting of the 5d levels of Eu²⁺ and Ce³⁺ all appear to be linearly related to one another. The values for Eu²⁺ are about 0.7 times those for Ce³⁺. This implies that spectroscopic properties known for Ce³⁺ can be employed to roughly predict spectroscopic properties for Eu²⁺ and vice versa. The findings for Ce³⁺ and Eu²⁺ can be generalized to all trivalent and divalent lanthanides.

Results of superconducting transition temperature measurements are presented for the bulk metallic glass Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 before and after annealing. The superconducting critical temperature T_c is 1.84 K for the as-prepared metallic glassy sample and 3.76 K for the annealed sample at zero magnetic field, respectively. The temperature gradient (−dH_c2/dT)_Tc of the upper critical field H_c2 near the critical temperature T_c of the bulk metallic glass Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 is about 2.5 T K⁻¹. Annealing of the metallic glass leads to a decrease of (−dH_c2/dT)_Tc to 1.2 T K⁻¹. The origin of the reduction of the critical temperature T_c in the amorphous Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5 is ascribed to a smearing of the density of states by the disordered atomic structure.

The thermal expansion and the magnetic susceptibility under ambient pressure and the temperature dependence of electrical resistivity under applied pressures for β-Mn_1−xOs_x alloys have been investigated. The concentration dependence of the spontaneous volume magneto-striction at 0 K, ω_mag(0), exhibits a broad maximum at about x = 0.14. The thermal expansion characteristic is explained qualitatively by the unified model based on the self-consistent renormalization theory. A weak itinerant-electron antiferromagnetic state in the β-Mn_1−xOs_x alloys varies with x to an intermediate state. The pressure coefficient of the Néel temperature decreases with increasing x, in accord with the variation of the magnetic state.

The influence of the rotation of a particle's magnetic moment in the magnetic anisotropy field on the shape of the Mössbauer spectra of hyperfine structure is analysed theoretically. It is found that, due to rotation, a renormalization of the nuclear g-factors occurs, which results in a qualitative transformation of Mössbauer absorption spectra. In particular, along with the magnetic sextet which is well known in the Mössbauer spectroscopy of the ⁵⁷Fe isotope, partial spectra can be formed that consist of 'magnetic' quintuplet, quartet, triplet and even doublet lines. This peculiarity in forming the spectra of magnetic hyperfine structure should be taken into account in analysing the Mössbauer spectra of materials with nano-sized magnetic particles.

Within the ballistic transport picture, we have investigated the spin-polarized transport properties of a ferromagnetic metal/two-dimensional semiconductor (FM/SM) hybrid junction and an FM/FM/SM structure using quantum tunnelling theory. Our calculations indicate explicitly that the low spin injection efficiency (SIE) from an FM into an SM, compared with a ferromagnet/normal metal junction, originates from the mismatch of electron densities in the FM and SM. To enhance the SIE from an FM into an SM, we introduce another FM film between them to form FM/FM/SM double tunnel junctions, in which the quantum interference effect will lead to the current polarization exhibiting periodically oscillating behaviour, with a variation according to the thickness of the middle FM film and/or its exchange energy strength. Our results show that, for some suitable values of these parameters, the SIE can reach a very high level, which can also be affected by the electron density in the SM electrode.

Recently, the observation of a new monoclinic phase in the PbZr_1−xTi_xO₃ (PZT) system in the vicinity of the morphotropic phase boundary was reported. Investigations of this new phase were reported using different techniques such as high-resolution synchrotron x-ray powder diffraction and Raman spectroscopy. In this work, the monoclinic → tetragonal phase transition in PbZr_0.50Ti_0.50O₃ ceramics was studied using infrared spectroscopy between 1000 and 400 cm⁻¹. The four possible ν₁-stretching modes (Ti–O and Zr–O stretch) in the BO₆ octahedron in the ABO₃ structure of PZT in this region were monitored as a function of temperature. The lower-frequency mode ν₁-(Zr–O) remains practically unaltered, while both intermediate ν₁-(Ti–O) modes decrease linearly as temperature increases from 89 to 263 K. In contrast, the higher-frequency ν₁-(Ti–O) and ν₁-(Zr–O) modes present anomalous behaviour around 178 K. The singularity observed at this mode was associated with the monoclinic → tetragonal phase transition in PbZr_0.50Ti_0.50O₃ ceramics.

In this paper we present results on green emission from Er³⁺-doped amorphous SiN alloys as a function of temperature and thermal annealing. It is shown that the lifetime of the green emission from the as-deposited sample decreases by an order of magnitude as the temperature increases from 5 to 300 K. Processes such as multiphonon decay and thermalization of the ²H _11/2 and ⁴S _3/2Er³⁺ levels are investigated in order to explain such behaviour. Concerning the effect of thermal annealing, our results show the activation of a new Er³⁺ site, whose nature may be related to the oxidation of the films.

Optical absorption and room temperature photoluminescence (PL) properties of nanometre AgI–silica composite synthesized by a simple heating–quenching method were investigated. The absorption of quenched AgI–silica was enhanced markedly. Three absorption bands at 440 (2.8 eV), 260 (4.8 eV) and 220 nm (5.6 eV) were observed. The excitonic absorption of AgI showed a red shift of ∼0.11 eV, in contrast to the usually observed blue shift in AgI nanocrystals. Besides two UV emissions from a non-bridging hole centre and E' centre defects formed in silica, the composite exhibited two PL emissions at 2.62 and 2.40 eV. The 2.62 eV PL was ascribed to donor–acceptor recombination of AgI, while the 2.40 eV one may correlate with energy levels induced by the interaction between silica and AgI. The role of silica in improving the PL for nanometre AgI is discussed.

In this paper we present results on cooperative luminescence performed on Yb³⁺-doped metaphosphate glasses under 980 nm excitation. We have measured emission spectra and decay lifetimes in the visible and infrared regions as a function of Yb concentration. It was observed that, up to 10% of Yb concentration, cooperative emission increases while lifetime is observed to decrease. Such behaviour is attributed to the Yb interaction with OH⁻ radicals and energy migration among Yb ions.