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Growth topographies of CaF₂(111) after molecular beam growth of CaF₂ at T = 1055 K for different saturation ratios S>1 and layer thickness were inspected by atomic force microscopy (AFM). Growth steps one triple layer high run mostly in directions, where those of type I prevail. Macrosteps resulting from a step bunching of triple layer steps are observed only for the directions. Macrosteps resulting from a pile-up of type I triple layer steps are steeper than those from type II steps. This can be attributed to a theoretically predicted attractive interaction between type I steps at distances closer than 1 nm.

This letter reports a giant magnetocaloric effect (GMCE) in a novel series of materials based on the shape memory alloy Ni₂MnGa. The origin of an enhanced GMCE is traced to the coincidence of a first-order magnetic transition and its attendant structural phase transition with a second-order magnetic transition. This coincidence is achieved by careful compositional tuning and is a technique which provides a criterion for enhancing the GMCE in this system. Thus, for Ni_55.2Mn_18.6Ga_26.2, we report an entropy change ΔS_m = −20.4 J kg⁻¹ K⁻¹ at 317 K in a field of 5 T. This shape memory system also has the added advantage of being formed from inexpensive, non-toxic constituents. With a working temperature at and above room temperature, it appears to be a most promising candidate for practical room temperature magnetic refrigeration.

The dynamic structure factor, S(Q,ω), of dense Hg vapour has been measured by high resolution inelastic x-ray scattering for densities of 3.0, 2.1 and 1.0 g cm⁻³ corresponding to 0.52, 0.36 and 0.17 times the critical density, respectively, and for momentum transfers between 2.0 and 48 nm⁻¹. Analysis of the longitudinal current–current correlation function in the framework of generalized hydrodynamics reveals that the frequencies of the collective excitations increase faster with Q than estimated from the macroscopic speed of sound. The ratios of the frequencies were found to be 1.27 at 3.0 g cm⁻³, 1.12 at 2.1 g cm⁻³ and 1.10 at 1.0 g cm⁻³. The sound velocity obtained from the present experiments is well reproduced by a wavenumber dependent adiabatic sound velocity, which means that the collective modes remain in the spectra of dense Hg vapour.

The neutron scattering technique is a relevant tool for studying the dynamical properties of electron transfer proteins. Macromolecular motions ranging in wide temporal and spatial windows can be investigated by separately analysing elastic, inelastic and quasielastic incoherent neutron scattering. The dynamical behaviour of the solvent surrounding a macromolecule can also be analysed. Neutron scattering is particularly rewarding when used in combination with molecular dynamics simulations. From the simulated atomic trajectories, physical quantities directly related to the neutron scattering technique can be calculated and compared with the corresponding experimental data. This article briefly introduces both the neutron scattering and molecular dynamics simulation methods applied to proteins, and reviews the biophysical studies of some electron transfer proteins. Both experimental and molecular dynamics results for these proteins and the surrounding solvent are also discussed in connection with their electron transfer properties. Possible developments are briefly outlined.

While all the information required for the folding of a protein is contained in its amino acid sequence, one has not yet learned how to extract this information in order to predict the three-dimensional, biologically active, native conformation of a protein whose sequence is known. Using insights obtained from simple model simulations of the folding of proteins, in particular the fact that this phenomenon is essentially controlled by conserved (native) contacts among (few) strongly interacting ('hot'), as a rule hydrophobic, amino acids, which also stabilize local elementary structures (LES, hidden, incipient secondary structures such as α-helices and β-sheets) formed early in the folding process and leading to the postcritical folding nucleus (i.e. the minimum set of native contacts which brings the system beyond the highest free-energy barrier found in the whole folding process) it is possible to work out a successful strategy for reading the native structure of designed proteins from a knowledge of only their amino acid sequence and of the contact energies among the amino acids. Because LES have undergone millions of years of evolution to selectively dock to their complementary structures, small peptides made out of the same amino acids as the LES are expected to selectively attach to the newly expressed (unfolded) protein and inhibit its folding, or to the native (fluctuating) native conformation and denature it. These peptides, or their mimetic molecules, can thus be used as effective non-conventional drugs to those already existing (and directed at neutralizing the active site of enzymes), displaying the advantage of not suffering from the increase in resistance.

The density and the specific heat of liquid Au–Cu alloy above and below the melting temperature are investigated in a wide composition range via constant temperature and constant pressure molecular dynamics simulations. The atomic interaction of the alloy is described with the embedded-atom method (EAM). The equilibrium melting temperature is evaluated from the change in the growth direction of a crystal–liquid sandwich structure under annealing. The simulated density of the Au–Cu alloy increases linearly with decrease of the temperature, whereas the specific heat remains constant over the entire temperature range of 900–1900 K. The excess volume is calculated according to the predicted density of Au–Cu alloy. The negative value of the excess volume and the exponential concentration dependence of the specific heat indicate that the Neumann–Kopp rule does not apply to the Au–Cu binary alloy system.

Li⁺-ion conducting glasses of (LiCl)_x(LiPO₃)_1−x with high LiCl compositions up to x = 0.45 were prepared successfully by using a twin-roller quenching method. ⁷Li magic angle spinning (MAS) NMR spectra of the glasses showed a broad signal, and a linear dependence of the chemical shift on LiCl composition, x, was observed. The chemical shift estimated by extrapolating the linear relation to the LiCl composition limit of x = 1 was very different from that of crystalline LiCl, and was concluded to correspond to that of amorphous LiCl. A linear relation to the LiCl composition was also observed for the linewidth of the signal, and quite a sharp signal was expected for amorphous LiCl from the relation. The glasses with relatively high LiCl compositions of exhibited a sharp signal besides the broad one in the spectra, and the chemical shift of the sharp signal corresponded well with that estimated for amorphous LiCl. This result clearly shows the formation of 'amorphous LiCl aggregate regions' in the (LiCl)_x(LiPO₃)_1−x glasses with increase of the LiCl composition, and the sharp signal was reasonably attributed to the Li⁺ ions included in the amorphous LiCl aggregate regions.

We report measurements of the glass transition temperature (T_g) in thin free-standing polymer films of polystyrene (PS) by means of confocal Raman spectroscopy. The paper introduces Raman spectroscopy as a novel method for the determination of T_g in polymer thin films. We find excellent agreement between Raman scattering and previously reported values of T_g obtained from either Brillouin scattering or ellipsometry. Further possible applications of the method to more complex conjugated polymers are briefly discussed.

Nd:Ba₂NaNb₅O₁₅ (Nd:BNN), Nd:Ba₂KNb₅O₁₅ (Nd:BKN) and Ba_1.90Nd_0.26 Li_0.42Nb₅O₁₅ (BNdLN) single crystals with the tetragonal tungsten–bronze (TTB) structure have been grown by means of the 'flux growth' method. The 10 and 298 K absorption and emission spectra and the room temperature decay curves have been measured and discussed in the light of the crystallographic information. The room temperature absorption spectra of Nd:BKN and BNdLN have been analysed in the framework of Judd–Ofelt theory and the Ω_λ (λ = 2, 4, 6) intensity parameters have been evaluated. The structural and emission properties of a new TB phase, Nd:Ba₂LiNb₅O₁₅ (Nd:BLN), have also been reported because they are useful in the discussion concerning the site occupancy of the active ions in these materials.

Photonic band structures are investigated for both diamond and hexagonal diamond crystals composed of dielectric spheres, and absolute photonic band gaps (PBGs) are found in both cases. In agreement with both Karathanos and Moroz's calculations, a large PBG occurs between the eighth and ninth bands in diamond crystal, but a PBG in hexagonal diamond crystal is found to occur between the sixteenth and seventeenth bands because of the doubling of dielectric spheres in the primitive cell. To explore the physical mechanism of how the photonic band gap might be broadened, we have compared the electric field distributions (|E|²) of the 'valence' and 'conduction' band edges. Results show that the field intensity for the 'conduction' band locates in the inner core of the sphere while that of the 'valence' band concentrates in the outer shell. With this motivation, double-layer spheres are designed to enhance the corresponding photonic band gaps; the PBG is increased by 35% for the diamond structure, and 14% for the hexagonal diamond structure.

Recently, Coulomb blockade physics was observed at room temperature in a carbon nanotube single-electron transistor (Postma et al 2001 Science293 76). In this work, we suggest that these devices may be promising for observing 2-channel Kondo physics, and allow for a detailed investigation of the 2-channel Kondo fixed point. Experimental signatures of the Kondo effect in these systems are discussed.

The first in situ Raman study of C₆₀ isothermal compression at 800 K and up to 32 GPa was performed using rhombohedral and tetragonal phases as starting materials. The rhombohedral phase shows a phase transition to 3D polymer above 10 GPa, similar to that in experiments where isobaric heating was used at pressures of 9–13 GPa. It is shown that the T–P diagram of C₆₀ polymeric phases (temperature increase followed by pressurizing) is significantly different from the known P–T diagram (pressurizing followed by heating). Tetragonal polymer exhibited significantly stronger stability and can be followed at least up to  GPa. Heating up to 800 K of tetragonal polymer at pressures of 6–8 GPa confirms that, due to geometrical frustrations, the tetragonal phase remains stable even at pressure and temperature conditions at which rhombohedral polymer is usually formed.

Electrodeposition of NiFe₂ alloy from a non-aqueous ethylene glycol sulfate bath followed by electrochemical oxidation (anodization) of the alloy in an aqueous bath at room temperature is described as a novel electrochemical process to deposit spinel nanocrystalline NiFe₂O₄ thin films on different conducting substrates. Various electrochemical parameters such as bath composition, current density, deposition time and bath temperature for electrodeposition of the NiFe₂ alloy and its anodization have been studied and optimized to obtain good quality NiFe₂O₄ films. The crystal structure, composition, surface morphology and microstructure of the films have been studied using a variety of techniques. Air annealing of the as-deposited NiFe₂O₄ thin films at 500 °C for 5 h improves the crystallinity and morphology of the films.

In this paper we present the results of the first systematic investigation of the geometrical properties of sodium nanoclusters in NaCl using the combined results of differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The melting behaviour of the sodium nanoclusters which had been produced in NaCl by electron beam irradiation up to a dose of 200 MGy has been studied by means of DSC. The sodium colloids have been visualized by AFM and their size distribution has been evaluated for two irradiation doses. The DSC scans of the irradiated samples exhibit two melting peaks located at temperatures below the melting temperature of bulk sodium. A phenomenological model has been proposed which explains this behaviour by the existence of two different structural states in the population of sodium colloids. We believe that small sodium clusters inherit the FCC structure from the surrounding Na sublattice in the NaCl matrix. When a small colloid grows, its lattice structure eventually transforms into the BCC structure of bulk sodium. The model results have been compared with the DSC measurements and the transition radius for the two structural states has been estimated.

Electron and positron backscattering coefficients are analytically calculated for a number of selected atomic targets in the energy range 1–10 keV and for incident angles between 0° and 80°. The dependence of the backscattering coefficient on the material, on the projectile primary energy and on the incidence angle has been examined and discussed. Our results are found to be in better agreement with experiment than earlier Monte Carlo simulations.

Polarized first- and second-order Raman scattering and infrared reflection spectra of hexagonal HoMnO₃ single crystals in the temperature range 10–300 K are reported. Based on the symmetry analysis and comparison with the results of lattice dynamics calculations the observed lines are assigned to the lattice eigenmodes. The magnetic ordering of Mn ions, which occurs below T_N = 76 K, is shown to affect Raman- and infrared-active phonons, which modulate Mn–O–Mn bonds and, consequently, the Mn–Mn exchange interaction.

Resistivity and magnetoresistance measurements have been performed on insulating icosahedral AlPdRe quasicrystal (QC) bar samples. At temperatures in the range , the resistivities follow a simple inverse temperature law: ρ(T) = ρ₀/T^{(1.0 ± 0.1)}. Below 1 K, the resistivity of a weakly insulating sample exhibited a simple inverse temperature law where ρ(T) = ρ₀/T^0.33 and not an activated variable-range hopping (VRH) law. Strongly insulating samples exhibit saturation of their resistivities to finite values as . These saturation resistivity values are believed to arise from the presence of a second metallic phase located within the quasicrystal's structure. By extrapolating the measured resistivities at 22 mK to absolute zero, the saturation conductivity values were estimated at T = 0 K and subtracted from the conductivity data points. These 'corrected' data, corresponding only to the QC phase, were found to follow activated VRH laws, having hopping exponents y that vary in the range . The activated VRH behaviours are observed only below 1 K. The magnetoresistances (MRs) of these samples are also anomalous. The MRs can be explained by including contributions from both the saturation conductivity values and from the QC MR ratios, estimated using the wavefunction shrinkage model.

The aim of this work was to study Cu–Ni alloys and establish a relation between alloy concentration and infrared emittance for wavelengths of the order 10 µm, which is of interest in room temperature applications. The resistivity was measured at room temperature for the same alloy compositions as the emittance in order to investigate the validity of the Hagen–Rubens relation in the infrared wavelength range for Cu–Ni. The Hagen–Rubens relation is verified for both the copper-rich and nickel-rich samples. We therefore assume strong electron scattering from impurities so that intraband transitions dominate over interband transitions in the infrared wavelength range. The validity of the Hagen–Rubens relation can, as a good approximation, also be used for the integrated thermal emittance.

The molecular orbitals of -biphenyl--dimethyldithiol (HS–CH₂–C₆H₄–C₆H₄–CH₂–SH) are identified from combined photoemission and inverse photoemission studies and compared with theory for several different surfaces, molecular conformations and molecular orientations. The preferential molecular orientations of biphenyldimethyldithiol, on both Au(111) and polycrystalline Co, are identified from polarization resolved photoemission studies. Two different molecular orientations are adopted by biphenyldimethyldithiol on gold depending on adsorption conditions. Biphenyldimethyldithiol is observed to bond more strongly to cobalt than gold surfaces.

We propose a non-JWKB-based theory of electron field emission for carbon field emitters in which, for electrons with energy in the vicinity of the order of ϑ to the Fermi level, the effective (1/x) surface potential is strongly enhanced. The model grossly violates the WKB validity criteria and necessitates an analytic treatment of the one-dimensional Schrödinger equation, which we first obtain. We determine ϑ (which is field-dependent) from the wavefunction matching point close to the surface. For reasonable values of the surface parameters—work function –5 eV, electron affinity and an empirical electron loss factor (and with no other adjustable parameters)—the theory provides an intriguing agreement with experimental data from carbon epoxy graphite composite (PFE) and certain graphitized carbon nanotube field emitters. We speculate on the surface potential enhancement, which can be interpreted as a massive (field-induced) dielectric effect of dynamic origin. This can be related via time-dependent perturbation theory to second-order non-linear polarizability enhancements at ultraviolet wavelengths near the tunnelling region. Finally some exact mathematical results are included in the appendix for future reference.

The thermopower, S, of La_0.7Ca_0.3Mn_1−yFe_yO₃ (y = 0–0.09), measured for T = 25–310 K and magnetic fields of B = 0–10 T, exhibits strong sensitivity to doping with Fe. The weak increase of S observed in the undoped material with lowering temperature is enhanced considerably in the sample with y = 0.03 until a steep decrease takes place in the vicinity of the paramagnetic–ferromagnetic transition temperature, T_C. S increases with further growth of y and its maximum follows the decrease of T_C from 228 K at y = 0.03 to 119 K at y = 0.09. Application of a magnetic field reduces S strongly. The experimental data are analysed quantitatively with a percolation model using results of our recent investigations of the Shklovskii–Efros-like variable-range hopping conductivity in the same set of La_1−xCa_xMn_1−yFe_yO₃ samples with evidence for a soft Coulomb gap and a rigid gap in the density of states near the Fermi level (Laiho et al 2002 J. Phys.: Condens. Matter14 8043). In the paramagnetic insulating phase the temperature dependence of S is determined by competing contributions from two types of asymmetry of the gap: a small shift of its centre with respect to the Fermi level and cubic non-parabolicity. Numerical values of the shift and the cubic asymmetry terms are determined.

The model periodic Coulomb interaction (Williamson et al 1997 Phys. Rev. B 55 R4851) is a replacement for the Ewald sum, developed to reduce finite-size errors in the simulation of extended 3D systems. We investigate the generalization of this technique to quasi-2D systems; we show through testing in quantum Monte Carlo simulations that while the new interaction reduces the calculation time dramatically it does not reduce finite-size errors. We explain this by analysing the finite-size errors generated when using the Ewald sum.

Pd-metal graphite (Pd-MG) has a layered structure, where each Pd sheet is sandwiched between adjacent graphene sheets. The DC magnetization and AC magnetic susceptibility of Pd-MG have been measured using a SQUID magnetometer. Pd-MG undergoes a superconducting transition at T_c (= 3.63 ± 0.04 K). The superconductivity occurs in the Pd sheets. The irreversibility between χ_ZFC and χ_FC occurs well above T_c. The susceptibility χ_FC obeys a Curie–Weiss behaviour with a negative Curie–Weiss temperature (). The growth of magnetic order is limited by the disordered nature of nanographites, forming magnetic short-range order at low temperature in the graphene sheets.

In this paper three different ways to calculate the temperature dependent susceptibility of the enhanced paramagnets Pd and Pt are presented and compared. Special attention is paid to the relative importance of one-particle and many-particle excitations. One of these methods has never been applied before to real itinerant systems. It is based upon Onsager's reaction field model, which seems to be a feasible and rigorous way to go beyond the mean field approximation, and it allows one to make quantitative statements. The backbone of this theory is the calculation of a temperature dependent Hubbard U due to thermal many-body excitations. In contrast to an earlier calculation we found a significant temperature dependence of U for Pd. The theoretical results are in fairly reasonable agreement with the experimental findings for both Pd and Pt.

We have probed the quasicrystalline state in binary YbCd_5.7 by monitoring its electrical resistivity between 1.5 and 300 K in externally applied hydrostatic pressure up to 16 kbar and measuring its magnetoresistivity up to 12 T from 0.5 to 20 K. The thermal variation of the resistivity is practically unaffected by pressure, indicating the stability of the quasicrystalline state in this pressure regime. A positive magnetoresistance, Δρ/ρ, of is observed at 0.65 K, which reduces to at 20 K in the maximum applied field of 12 T. Though the magnetoresistance of the sample investigated is about an order of magnitude larger than expected on the basis of the empirically derived relationship observed for a large number of quasicrystals, it is much below the unusually large anomalous magnetoresistance (20–200%) reported earlier in the literature. We believe that the intrinsic magnetoresistivity of YbCd_5.7 in different samples may be primarily masked by the presence of traces of free Cd which is known to have a giant magnetoresistivity at low temperatures.

The results from a series of Monte Carlo simulations are presented for the two-dimensional Heisenberg model consisting of classical spin vectors arranged on the vertices of a square lattice in which the spins interact through an antiferromagnetic exchange interaction, a magnetic surface anisotropy and the dipolar interaction. The simulations focus on the exchange dominated regime in which the strength of the exchange interaction is significantly greater than both the dipolar interaction and the magnetic surface anisotropy. The results from the simulations show that there exists a range of the magnetic surface anisotropy parameter values in which the system exhibits a reorientation transition from a planar antiferromagnetic phase at low temperature to a perpendicular antiferromagnetic phase at higher temperature. The phase diagram, obtained from the Monte Carlo calculations, is determined as a function of both temperature and magnetic surface anisotropy parameter for a fixed value of the exchange constant. In addition, the low temperature magnetization data suggests a softening of a spin wave stiffness close to the phase boundary between the two ordered states.

The magnetic environment of tin in the ferromagnetic superconductor RuSr₂GdCu₂O₈ has been probed by doping ¹¹⁹Sn ions onto the ruthenium sites. The transferred magnetic hyperfine interaction at the tin site was measured by Mössbauer spectroscopy in the temperature range 4.2–300 K. The spectra show two distinct tin sites. One has four ruthenium nearest-neighbour cations and the other three ruthenium and one tin nearest neighbours. The temperature dependence of the hyperfine fields indicates an ordering temperature of 108 ± 5 K. The spectra favour parallel alignment of the field with the major axis of the electric field gradient indicating that the ruthenium moments are aligned along the crystallographic c axis.

We investigate the gradual crossover from ferroelectric to relaxor behaviour versus substitution in lead-free ceramics. We show that the Vogel–Fulcher law in the relaxor state is the extrapolation of the ferroelectric line. To explain this extrapolation, we suggest that both the host matrix and the impurity induced clusters are triggered by the BaTiO₃ soft mode correlation length. The Ti–O bond oscillations are the key mechanism.

We have studied the wavevector dispersion of the L₊ coupled mode in n-type In_0.53Ga_0.47As by means of Raman scattering using several excitation wavelengths in the range between 457.9 and 720 nm. The optical properties of In_0.53Ga_0.47As in the range of excitation energies used are strongly affected by the presence of the E₁ and E₁+Δ₁ critical points, and set an upper limit to the wavevector that can be probed by decreasing the excitation wavelength in Raman scattering experiments. The Raman scattering results are analysed using a Lindhard–Mermin model, and it is found that optical absorption strongly affects the coupled-mode Raman peaks excited with the more energetic lines.

We present soft x-ray fluorescence measurements of skutterudite compounds (CoAs₃ and CoSb₃). Our results are compared with x-ray photoelectron spectra (XPS) and band structure calculations. The occupancy of d states is found to increase in transition metal antimonides with respect to that of pure metals. The experimental spectra are interpreted in terms of our LDA band structure calculations and we find that electron correlation does not have to be taken into account. The intensity ratio of the Co L₂ to L₃ emission lines is found to be 0.20 and 0.15 for CoAs₃ and CoSb₃, respectively, which we attribute to the decrease in Coster–Kronig processes in CoAs₃ compared to CoSb₃ with its smaller carrier density. The calculated values of the thermoelectric figures of merit show that CoSb₃ is the most promising thermoelectric material, which is in accordance with experimental measurements of the electrical conductivity and Seebeck coefficient.

A new dynamical method is employed to study charge transfer probabilities between a donor and an acceptor coupled via a long π-conjugated bridge, within a correlated many-body picture. The initial state of the composite system (donor + bridge + acceptor) is taken to be the direct product of the ground state of the bridge Hamiltonian with specified occupancies in the donor and the acceptor orbitals. This t = 0 state is evolved using the many-body model Hamiltonian of the composite system. We find that for the interacting model, the rate of electron transfer depends strongly on the initial occupancy of the acceptor orbital. The electron transfer rate is quite different from the spin exchange rate and emphasizes the spin-charge separation in one-dimensional Hubbard models.

Experimental magnetic field dependent Hall and resistivity data are presented for n-GaAs homojunction far-infrared (FIR) detector structures in the temperature range from 1.8 to 200.0 K and with a magnetic field up to 15 T. The carrier transport properties of the multilayer/multicarrier structure have been separated and quantified individually by a hybrid approach consisting of mobility spectrum analysis followed by a multicarrier fitting procedure. The observed temperature dependence of mobility and concentration is explained using classical band theory, which unambiguously reveals highly doped degenerate contact layers and semiconductor–metal transition in emitter layers. The detailed analysis of the concentration and the Fermi level in the emitter layers gives clear evidence for the formation of GaAs homojunction FIR detection occurring at the interfaces between the emitter and intrinsic layers.

In a recent paper, Keen and Lovesey (KL) (2003 J. Phys.: Condens. Matter15 4937) presented a theoretical model to account for lines of intensity, in addition to Bragg peaks, observed by Fillaux, Cousson and Keen (FCK) (2003 Phys. Rev. B 67 054301 and 2003 Phys. Rev. B 67 189901 (erratum)) in single-crystal neutron diffraction measurements on potassium hydrogen carbonate (KHCO₃). In this comment it is demonstrated that KL's model is irrelevant and cannot account for the data under consideration.