Table of contents

In order to fabricate ordered arrays of nanostructures, two different strategies might be considered. The `top-down' approach consists of pushing the limit of lithography techniques down to the nanometre scale. However, beyond 10 nm lithography techniques will inevitably face major intrinsic limitations. An alternative method for elaborating ultimate-size nanostructures is based on the reverse `bottom-up' approach, i.e. building up nanostructures (and eventually assemble them to form functional circuits) from individual atoms or molecules. Scanning probe microscopies, including scanning tunnelling microscopy (STM) invented in 1982, have made it possible to create (and visualize) individual structures atom by atom. However, such individual atomic manipulation is not suitable for industrial applications. Self-assembly or self-organization of nanostructures on solid surfaces is a bottom-up approach that allows one to fabricate and assemble nanostructure arrays in a one-step process. For applications, such as high density magnetic storage, self-assembly appears to be the simplest alternative to lithography for massive, parallel fabrication of nanostructure arrays with regular sizes and spacings. These are also necessary for investigating the physical properties of individual nanostructures by means of averaging techniques, i.e. all those using light or particle beams.

The state-of-the-art and the current developments in the field of self-organization and physical properties of assembled nanostructures are reviewed in this issue of Journal of Physics: Condensed Matter. The papers have been selected from among the invited and oral presentations of the recent summer workshop held in Cargese (Corsica, France, 17–23 July 2005). All authors are world-renowned in the field. The workshop has been funded by the Marie Curie Actions: Marie Curie Conferences and Training Courses series named `NanosciencesTech' supported by the VI Framework Programme of the European Community, by the EUROCORES SONS Programme under the auspices of the European Science Foundation and the VI Framework Programme of the European Community. It was also funded by CNRS `formation permanente'.

Major topics relevant to self-organization are covered in these papers. The first two papers deal with the physics of self-organized nucleation and growth. Both metal and semiconductor templates are investigated. The paper by Meyer zu Heringdorf focuses on the mesoscopic patterns formed by the Au-induced faceting of vicinal Si (001). Repain et al describe how uniform and long-range ordered nanostructures are built on a surface by using nucleation on a point-defect array. Electronic properties of such self-organized systems are reviewed by Mugarza and Ortega. The next three papers deal with molecules and self-organization. In the paper presented by Kröger, molecules are deposited on vicinal Au surfaces and are studied by STM. A very active field in self-organized nanostructures is the chemical route for nanoparticle synthesis. The paper by Piléni deals with self-organization of inorganic crystals produced by evaporation of a solution, also called colloids. Their physical properties are also treated. Gacoin et al illustrate chemical synthesis, including the template approach, using organized mesoporous silica films for the production of semiconductor or metal arrays of particles. An alternative method is developed in the paper by Allongue and Maroun which is the electrochemical method of building arrays of nanostructures. Ultimately, self-organization is a very interdisciplinary field. There is also an attempt in this issue to present some of the challenges using biology. The paper by Belamie et al deals with the self-assembly of biological macromolecules, such as chitin and collagen. Finally, Molodtsov and co-workers describe how a biological template can be used in order to achieve novel materials made of hybrid metallo-organic nanostructures.

Vicinal Si(001) surfaces with ≈4° miscut toward [110] consist of ordered terraces that are separated by a double step every 4 nm. Adsorption of Au at 800–900 °C changes the step morphology dramatically: after a critical Au coverage of 1/3 ML is reached, Au condenses from an initially formed lattice gas into a (5 × 3.2) reconstruction on newly formed (001) terraces. The steps of the vicinal surface are accumulated in irregular step bunches to conserve the macroscopic miscut. With increasing Au coverage the step bunches are transformed into well defined facets. The ultimate facet orientation depends on the adsorption temperature, although at temperatures above T = 800 °C only (001) terraces and (119) facets are observed. Depending on the deposition temperature, the terraces and facets exhibit a periodicity from 200 nm to 4 µm and a structural length of up to several millimetres. Illumination with white light under grazing incidence results in a colourful striped pattern in an optical microscope. A novel in situ light diffraction experiment is presented, that is perfectly matched to the mesoscopic dimensions of the faceted surfaces. Illumination with a He–Ne laser during and after deposition results in complex diffraction patterns that can be used to estimate the length of the terraces. The temperature dependence of the terrace length shows an Arrhenius behaviour with an activation energy of E_A≈2.8 eV during the initial stages of the faceting; at T = 825 °C the terraces extend with a constant velocity of 30 µm s⁻¹. This value is in excellent agreement with earlier low energy electron microscopy measurements.

We present both experimental and simulated results of ordered growth of cobalt nano-islands on a Au(111) vicinal template. Firstly, the temperature range for ordered growth and the islands size distributions are investigated by a rate equation model and kinetic Monte Carlo (KMC) simulations. Secondly, the incidence of the surface structure on the growth of cobalt is studied in detail by means of variable temperature scanning tunnelling microscopy experiments and KMC simulations. The underlying atomic processes responsible for the ordered growth are discussed.

Vicinal surfaces of the (111) plane of noble metals are characterized by free-electron-like surface states that scatter at one-dimensional step edges, making them ideal model systems to test the electronic properties of periodic lateral nanostructures. Here we use high-resolution, angle-resolved photoemission to analyse the evolution of the surface state on a variety of vicinal surface structures where both the step potential barrier and the superlattice periodicity can vary. A transition in the electron dimensionality is found as we vary the terrace size in single-phase step arrays. In double-phase, periodic faceted surfaces, we observe surface states that characterize each of the phases.

Using low-temperature scanning tunnelling microscopy and spectroscopy we investigated the adsorption characteristics of 3,4,9,10-perylenetetracarboxylic-dianhydride and fullerenes on Au(788), Au(433), and Au(778). On Au(788) and Au(778), 3,4,9,10-perylenetetracarboxylic-dianhydride exhibits three coexisting superstructures, which do not reflect the periodicity of the hosting substrate. The adsorption on Au(433) leads to the formation of molecule chains along the step edges after annealing the sample. Fullerene molecules on Au(788) arrange in a mesh of islands, which extends over several hundreds of nanometres with an extraordinarily high periodicity. A combination of fullerene adsorption and annealing leads to facetting of Au(433) and the formation of extraordinarily long fullerene stripes.

Self-organizations of inorganic nanocrystals in 1D, 2D and 3D superlattices are described. In the latter case, supra-crystals with face-centred-cubic (fcc) structure are demonstrated. Collective properties due to the nanocrystal organization are described. These properties are either intrinsic or due to dipolar interactions.

Tremendous work achieved in the last 20 years on nanoparticle synthesis has allowed us to study many new physical properties that are found in the nanometre size range. New developments are now expected when considering assemblies of nanoparticles such as 2D or 3D organized arrays. These systems are indeed expected to exhibit original physical properties resulting from particle–particle interactions. Studies in this field are clearly dependent on the elaboration of materials with controlled particle size, organization and interparticle distance. This paper presents a strategy of elaboration that is based on the use of organized mesoporous silica films as templates. These films are made by sol–gel polymerization around surfactant assemblies and further elimination of the surfactant. This provides porous matrices with a pore organization that is the almost perfect replica of the initial micellar structure. The use of such films for the elaboration of organized arrays of nanoparticles is detailed in the case of CdS and Ag particles. The formation of particles inside the pores is achieved through impregnation with precursors that are allowed to diffuse inside the pores. This leads to particles with a size and a spatial arrangement that is directly related to the initial pore structure of the films. This process opens a wide range of investigations due to the relative ease of fabrication over large surfaces and the numerous possibilities offered by the elaboration of porous films with different pore sizes and organizations.

This paper is a brief review of self-ordered electrochemical growth on single-crystal electrode surfaces on which arrays of nanostructures are created by replication of patterns made by atomic steps or surface reconstruction. Whenever possible the parallel is made between electrochemical growth and molecular beam epitaxy in ultrahigh vacuum. An atomistic view of electrodeposition is given first to help with identifying the similarities of and specific differences between the two techniques of growth. Recent examples where self-organized nanostructures are prepared on metals and silicon substrates are discussed.

Morphogenesis of extracellular matrices can be considered from different perspectives. One is that of ontogenesis, i.e., an organism's development, which is mostly concerned with the spatiotemporal regulation of genes, cell differentiation and migration. Complementary to this purely biological point of view, a physico-chemical approach can help in understanding complex mechanisms by highlighting specific events that do not require direct cellular control. Because of a structural similarity between some biological systems and liquid crystals, it was supposed that similar mechanisms could be involved. In this respect, it is important to determine the intrinsic self-assembly properties driving the ordering of biological macromolecules. Here we review in vitro studies of the condensed state of major biological macromolecules from extracellular matrices and related theories describing a mesophase transition in suspensions of rodlike particles. Dilute suspensions of collagen or chitin are isotropic, i.e., the macromolecules can take on any orientation in the fluid. Beyond a critical concentration, an ordered nematic phase appears with a higher volume fraction. The two-phase coexistence can be seen between crossed polarizers since the nematic phase is strongly birefringent and appears bright, whereas the isotropic phase remains dark. A widespread property of these structural macromolecular scaffolds is their chirality. Although the origin of chirality in colloidal suspensions is still a subject of debate, the helical nature of the cholesteric phase can be quantified. Small angle x-ray scattering performed on shear-aligned samples can help demonstrate the cholesteric nature of the anisotropic phase, inferred from optical observations. Liquid-like positional local order is revealed by the presence of broad interference peaks at low angle. The azimuthal profiles of these patterns are fitted to determine the value of the nematic order parameter at the transition. A few physico-chemistry experiments can assess the nature of the transition, and in turn, applying theoretical models can prove useful in predicting and controlling the structure of assemblies of biological macromolecules.

Photoemission (PE) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy were applied to characterize electronic properties of the regular two-dimensional bacterial surface protein layer (S layer) of Bacillus sphaericus NCTC 9602, which is widely used as a protein template for the bottom-up fabrication of advanced metallic and hybrid nanostructures. PE and NEXAFS at the C 1s, O 1s, and N 1s core levels show similar chemical states for each oxygen atom and also for each nitrogen atom, while carbon atoms exhibit a range of chemical environments in different functional groups of the amino acids. A series of characteristic NEXAFS peaks were assigned to particular molecular orbitals of the amino acids by applying a phenomenological building-block model. It was found that the π clouds of aromatic rings make the main contribution to both the lowest unoccupied and highest occupied molecular orbitals. The two-dimensional protein crystal shows a semiconductor-like behaviour with a gap value of ∼3.0 eV and the Fermi energy close to the bottom of the LUMO.

Two different polymers, with large local electric dipoles, are compared: copolymers of polyvinylidene fluoride with trifluoroethylene [P(VDF-TrFE, 70%:30%)] and polymethylvinylidenecyanide (PMVC). While the different local point group symmetries play a key role, both crystalline polymers exhibit intra-molecular band structure, though the Brillouin zone critical points differ.

The use of the neutron spin echo (NSE) technique in the study of slow dynamic processes in magnetic systems is reviewed. NSE provides the highest energy resolution of all inelastic neutron scattering techniques, hence it is used mainly in studying systems that show very slow dynamics, which cannot be resolved otherwise with neutrons. For spin glasses, which show a dramatic slowing down of the spin dynamics in the vicinity of T_g, research using NSE has made significant contributions to our understanding of the nature of the phase transition and the line shape of the spin relaxation function. In the study of the critical dynamics in magnets, NSE has proven predictions of dynamic scaling theory to be correct. Geometrically frustrated magnets and their unusual properties at low temperature have seen an upsurge of interest in recent years, and NSE has been able to make some key contributions to this field. The case of Gd₂Ti₂O₇ is presented in some detail, a system in which ordered spins and paramagnetic spins coexist.

We review the phenomenon of ferromagnetic resonance (FMR) in ferromagnetic (FM) Ga_1−xMn_xAs semiconductor alloys and their heterostructures in thin film form. We will show that the analysis of FMR in Ga_1−xMn_xAs films can directly provide values of cubic and uniaxial magnetic anisotropy fields in these materials—i.e. the anisotropy associated with the natural (undistorted) zinc-blende structure and that arising from strain-induced distortion, respectively. In addition to the effects of strain, in this review we will also discuss the use of FMR to determine the effects of annealing, temperature, and doping on magnetic anisotropy. The FMR results attained on the temperature dependence of anisotropy fields (both cubic and uniaxial) provide a natural explanation of the easy-axis reorientation transition that is observed in these materials as the temperature changes. Using results observed on Ga_1−xMn_xAs samples where the concentration of holes is controlled either by annealing or by modulation doping, we will show that FMR also provides a convenient tool for studying the correlation between hole concentration and magnetic anisotropy. Additionally, we will show that the FMR studies of Ga_1−xMn_xAs /Ga_1−yAl_yAs heterostructures modulation doped by Be reveal that the effective g-factor of Ga_1−xMn_xAs is also strongly affected by the doping. The measurements of the total g-factor can in turn be used to estimate the contribution which the holes themselves make to the total magnetization of Ga_1−xMn_xAs. Finally, we will review the results which are currently available on the FMR linewidth, including its dependence on temperature, angle of applied field, and annealing. Although the data on FMR broadening are at this time largely phenomenological, the dependence of the linewidth on hole concentrations suggests that the p–d coupling between the holes and the Mn²⁺ ions contributes significantly to the damping rate of the magnetization precession in FMR experiments on Ga_1−xMn_xAs films. Finally, it should be noted that—although in this review we focus on Ga_1−xMn_xAs, because the overwhelming majority of work on FMR has been carried out on this material—the description of FMR and its analysis presented here can be applied to thin layers of all III_1−xMn_xV alloys generally.

We studied hydrogen adsorption onto the oxidized nano-palladium surface using ¹H NMR. In the α phase, the incoming hydrogen molecules dissociate and form OH_ad. We confirm that the transformation occurs during the α–β phase transition by observing a decrease in OH_ad resonance intensity.

Mg_xZn_1−xO (MZO) thin films prepared by an rf magnetron sputtering technique are reported. The films were grown at room temperature and at relatively low rf power of 50 W. MZO thin films were found to possess preferred c-axis orientation and exhibited hexagonal wurtzite structure of ZnO up to a Mg concentration of 42 mol%. A small variation in the c-axis lattice parameter of around 0.3% was observed with increasing Mg composition, showing the complete solubility of Mg in ZnO. The band gap of the MZO films in the wurtzite phase varied linearly with the Mg concentration and a maximum band gap ∼4.19 eV was achieved at x = 0.42. The refractive indices of the MgO films were found to decrease with increasing Mg content. The observed optical dispersion data are in agreement with the single oscillator model. A photoluminescence study revealed a blue shift in the near band edge emission peak with increasing Mg content in the MZO films. The results show the potential of MZO films in various opto-electronic applications.

Here we present a development of multilayer-based optics for the extreme ultra-violet (EUV) and x-ray range. The authors discuss results of the study of optical performance of Mo/Si coatings with regard to the microstructure of metal layers, which was analysed by x-ray diffraction (XRD) and by transmission electron microscopy (TEM). We have demonstrated an ability to control the microstructure of the multilayers via optimization of the deposition process, which is important for various EUV and x-ray applications of multilayer optics.

We report an ion flux dependence study of the Si dot pattern formed on Si(100) by Ar⁺ ion sputtering with the ion energy being 1.5 keV, ion dose 5 × 10¹⁷ ions cm⁻², and ion flux ranging from 280 to 1100 µA cm⁻². Experimental results show that the lateral dot diameter d and the ion flux f basically follow the relationship of , and the surface roughness w decreases with increasing f in an exponential decay manner. Simulations based on a widely accepted continuum model, namely the noisy Kuramoto–Sivashinsky equation, reproduced the trend for d versus f but failed to explain that for w versus f. A redeposition consideration was then suggested. It is found that with this correction not only are the d–f and w–f relationships well explained, but the simulated surface morphology bears closer resemblance to the experimental one as well. The effect of redeposition becomes important for f> ∼130 µA cm⁻² as derived in this work.

Superlattices of [(La_0.7Sr_0.3MnO₃)₁₀/(BaTiO₃)₄]₂₅ were grown on (001)-oriented SrTiO₃ using the pulsed laser deposition technique. The magnetic and transport properties were studied as a function of the oxygen pressure. The suppressed magnetism and associated transport properties are discussed. A high value of magnetoresistance at low temperature with more pronounced hysteretic behaviour is observed for the superlattice grown at low oxygen partial pressure. Our results clearly suggest the importance of controlling the oxygen stoichiometry during the growth of the oxide superlattice to minimize the interface related problems.

In a substrate/ferromagnetic/antiferromagnetic/ferromagnetic trilayer, the exchange coupling occurring at the bottom ferromagnetic/antiferromagnetic interface is always found to be weaker than the one at the top antiferromagnetic/ferromagnetic interface after thermal treatment. We show clearly in this paper that this effect is related to the degree of magnetic disorder at the ferromagnetic/antiferromagnetic interface during the multilayer growth. The larger the magnetic disorder the weaker is the exchange bias field in the as-deposited bilayer, as expected, but, counterintuitively, the stronger is the exchange bias field after a subsequent in-field annealing.

In this work, the characterization of the roughness of a set of equipotential lines , due to a rough surface held at a nonzero voltage bias, is investigated. The roughness of the equipotential lines reflects the roughness of the profile, and causes a rapid variation in the electric field close to the surface. An ideal situation was considered, where a well known self-affine profile mimics the surface, while the equipotential lines are numerically evaluated using Liebmann's method. The use of an exact scale invariant profile helps to understand the dependency of the line roughness exponent on both the value of the potential (or on the average distance to the profile) and the profile's length. Results clearly support previous indications that: (a) for a system of fixed size, higher values of α characterize less corrugated lines far away from the profile; (b) for a fixed value of the potential, α decreases with the length of the profile towards the value of the boundary. This suggests that, for a system of infinite size, all equipotential lines share the same value of α.

We report measurements of transverse magnetoresistance where the signal can be attributed to electron–surface scattering, together with measurements of the surface roughness of the films on an atomic scale. The measurements were performed with a scanning tunnelling microscope (STM) on four thin gold films evaporated onto mica. The magnetoresistance exhibits a marked thickness dependence: at 4 K and 9 T is about 5% for the thinner (69 nm) film, and about 14% for the thicker (185 nm) film. Sondheimer's theory provides an accurate description of the temperature dependence of the resistivity, but predicts a magnetoresistance one order of magnitude smaller than that observed at 4 K. Calecki's theory in the limit of small roughness correlation length, predicts a resistivity two orders of magnitude larger than observed at 4 K.

We develop a numerical model to investigate the localization of surface exciton polaritons in the presence of random roughness and spatial dispersion. The localization criteria are examined. The localization effects are embodied in the large enhancement and rapid decay of the field intensity on the surface. The calculation shows that there is a transition from the localized state to the extended state. It has been found that the localization occurs in a limited frequency range above the resonant frequency of transverse excitons.

Antimony islands of different shapes and dimensions were grown on highly oriented pyrolytic graphite (HOPG) at room temperature in ultrahigh vacuum. Three-dimensional (3D) spherical, 2D thin films and 1D nanorods of Sb on graphite were studied using in situ scanning tunnelling microscopy. Sb was evaporated in the form of Sb₄, which interacts with HOPG weakly and exhibits a high surface mobility, resulting in preferential nucleation of 3D spherical islands at defect sites. Surface diffusion and aggregation lead to the formation of nanoparticles with various shapes and sizes. The shape and size of islands depend on growth parameters, i.e. flux and deposition time. The 3D and 2D structures of Sb on graphite have the same bulk crystalline rhombohedral (α-Sb) structure, but the 1D nanorods show a highly compressed structure different from the α-Sb lattice.

The temperature dependence of specific heat for the compounds CeNi₄Cu and YbNi₄Cu is analysed. These studies are supported by magnetic susceptibility and x-ray photoemission spectroscopy measurements. The scheme of the energy levels created by the splitting due to the crystal electric field is determined from the Schottky contribution to the specific heat. Anomalies observed at low temperatures are discussed in the framework of heavy-fermion/Kondo physics. It is found that an external magnetic field has a strong influence on the low temperature part of the specific heat.

Raman spectra have been measured on Cs₂HgBr₄ as a function of pressure, degree of hydrostaticity and location in the sample chamber. In the absence of a pressure-transmitting medium the title compound transforms reversibly into an amorphous phase at about 9 GPa, and this throughout the sample chamber. When argon is used as pressure-transmitting medium in a similar pressure range, different areas (with an approximate radius of 2 µm) of the pressure chamber yield dissimilar Raman spectra, varying from complete amorphization to a crystal-to-crystal transition. The results from this Raman study are combined with previous x-ray diffraction results and simulations on the same compound to give a comprehensive picture of the formation of a ferroelastic glass state.

In this paper we report the successful preparation of hafnium substituted barium titanate, i.e. BaTi_1−xHf_xO₃ (BHT) ceramics with (x = 0.05,0.1,0.2,0.3 and 0.4). X-ray diffraction measurements followed by Reitveld analysis show the single-phase nature of these ceramics undergoing a tetragonal to cubic phase transformation for x≥0.10. Temperature dependent dielectric properties (ε^' and ε^'') of these single-phase BHT ceramics have been studied in the temperature range 90–375 K and frequency range 0.1–100 kHz. Dispersionless but hysteric ε^'–T and ε^''–T behaviour has been observed for x<0.3 whereas for x≥0.3 highly diffusive and depressive ε^'–T and ε^''–T behaviour has been observed. The three different phase transitions of pure BaTiO₃ get pinched into a single diffused round peak along with frequency dispersion for x≥0.3. This clearly indicates an evolution of classical to relaxor ferroelectrics crossover with increasing x in these BHT ceramics. The parameters characterizing the relaxor behaviour have been analysed. The mechanism for the dielectric relaxation process and pinching of phase transition and their effect on ferroelectric behaviour is discussed.

Solid helium (³He and ⁴He) in the hcp and fcc phases has been studied by the path-integral Monte Carlo technique. Simulations were carried out in the isothermal–isobaric (NPT) ensemble at pressures up to 52 GPa. This allows one to study the temperature and pressure dependences of isotopic effects on the crystal volume and vibrational energy in a wide parameter range. The obtained equation of state at room temperature agrees with available experimental data. The kinetic energy, E_k, of solid helium is found to be larger than the vibrational potential energy, E_p. The ratio E_k/E_p amounts to about 1.4 at low pressures and decreases as the applied pressure is raised, converging to 1, as in a harmonic solid. Results of these simulations have been compared with those yielded by previous path integral simulations in the NVT ensemble. The validity range of earlier approximations is discussed.

A theory is proposed to describe the competition among antiferromagnetism (AF), spin glasses (SG) and the Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength J_K and an interlattice quantum Ising interaction in the presence of a transverse field Γ. The interlattice coupling is a random Gaussian distributed variable (with average −2J₀/N and variance 32J²/N) while the Γ field is introduced as a quantum mechanism to produce spin flipping. The path integral formalism is used to study this fermionic problem where the spin operators are represented by bilinear combinations of Grassmann fields. The disorder is treated within the framework of the replica trick. The free energy and the order parameters of the problem are obtained by using the static ansatz and by choosing both J₀/J and Γ/J≈(J_K/J)² to allow, as previously, a better comparison with the experimental findings. The results indicate the presence of a SG solution at low J_K/J and for temperature T<T_f (T_f is the freezing temperature). When J_K/J is increased, a mixed phase AF+SG appears, then an AF solution and finally a Kondo state is obtained for high values of J_K/J. Moreover, the behaviours of the freezing and Néel temperatures are also affected by the relationship between J_K and the transverse field Γ. The first presents a slight decrease while the second decreases towards a quantum critical point (QCP). The obtained phase diagram has the same sequence as the experimental one for Ce₂Au_1−xCo_xSi₃, if J_K is assumed to increase with x, and in addition it also shows a qualitative agreement concerning the behaviour of the freezing and the Néel temperatures.

The thermal expansion properties and melting points of silicon and germanium are calculated using molecular dynamics simulations within the density functional theory framework. An isothermal–isobaric (NPT) ensemble is considered in a periodic system with a relatively small number of particles per unit cell to obtain the thermal expansion data over a range of temperatures, and it is found that the calculated thermal expansion coefficients and bond lengths agree well with experimental data. Also, the positions of discontinuities in the potential energy as a function of temperature are in good agreement with the experimental melting points.

The photoluminescence of Ce³⁺ and Tb³⁺ ions in zinc metaphosphate glasses is investigated. The blue and green emissions of Tb³⁺ ions are enhanced upon UV excitation through energy transfer from Ce³⁺ to Tb³⁺ ions. The efficiency of such an energy transfer was estimated based on spectroscopic data and resulted in being about 20–23%. Spectroscopic data revealed that the energy transfer occurs via a non-radiative process inside Ce³⁺–Tb³⁺ clusters formed in the glass. This ion clustering could be useful for the design of efficient conversion phosphors of ultraviolet to blue and green light.

We apply a first-principles method based on the density functional theory within the generalized gradient approximation, and the full-potential linear augmented plane-wave method, to calculate the structural and electronic properties of cubic (BN)_xC_2(1−x) ordered alloys. We investigate the equilibrium lattice parameters, the bulk moduli, the density of states, the band-gap energies and the effective masses of the conduction and valence bands along the [111],[100] and [110] directions. The obtained results are used to provide effective-mass and Luttinger parameters, and to give an important guideline to the material's design for optoelectronic devices, we link the first-principles band calculations with effective mass theory.

The magnetic moment induced by an external magnetic field of 5.8 T on the Co³⁺ ions in LaCoO₃ has been measured by polarized neutron diffraction. Measurements were made at 100 K, near to the susceptibility maximum usually associated with a gradual spin-state transition, as well as at 1.5 and at 285 K. The data give evidence for a transition from the ground singlet state (S = 0) to the excited triplet intermediate spin-state (S = 1). The energy of Δ_H≈1000 K estimated for the high-spin-state (S = 2), is too high to make a significant contribution to the moment, even at T = 285 K. There is evidence for a small negative spin density associated with the oxygen ligands in agreement with the theory that predicts intermediate spin as the first excited state.

Highly HfO₂ doped lithium niobate crystals have been grown. The experimental results indicate that LiNbO₃:Hf (up to 4 mol%) can withstand the same light intensity, of 5 × 10⁵ W cm⁻², as LiNbO₃:Mg (6.5 mol%). And the OH⁻ absorption bands of these LiNbO₃:Hf crystals shift to 3487 cm⁻¹ from the 3484 cm⁻¹ for congruent pure LiNbO₃. The difference spectra and fitting treatments show that the OH⁻ absorption peak corresponding to (Hf_Nb⁴⁺)⁻–OH⁻ is located at 3500 cm⁻¹.