Table of contents

In an argon ICP RF discharge modulated by 1 kHz square pulses, strong emission at 549.6 nm (corresponding to the upper level Ar(6d)) was observed about 100 µs after the pulse termination in the afterglow. This emission exceeds by a factor of as much as five the duty-on cycle intensity. With simple kinetic considerations, we assigned this emission to the Penning pooling ionization of argon metastable atoms leading to the formation of in the afterglow followed by electron–ion recombination producing highly excited argon atoms Ar(6d). With the addition of 1% N₂ into Ar, the emission at 549.6 nm completely disappeared in the afterglow. This disappearance could be explained by excitation transfer between Ar metastable atoms and nitrogen molecules leading to the emission of the second positive system of N_2..

We demonstrate an intriguing liquid crystal display (LCD) mode that comprises an optically isotropic LC composite incorporating in-plane electric field geometry. No surface treatment, such as rubbing, is required to fabricate the LCD mode because it is based on an isotropic state. The measured response time is of submillisecond order. This rapid response originates from the local reorientation of molecules in small LC clusters as well as from strong polymer stabilization. The LCD mode has several unique features such as fast response, continuous greyscale capability and a high contrast ratio.

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br₂ into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 µm, corresponding to the grain size of the starting material.

Semiconductor nanocrystals have attracted considerable interest for a wide range of applications including light-emitting devices and displays, photovoltaic cells, nanoelectronic circuit elements, thermoelectric energy generation and luminescent markers in biomedicine. A particular advantage of semiconductor nanocrystals compared with bulk materials rests in their size-tunable optical, mechanical and thermal properties. While nanocrystals of ionically bonded semiconductors can conveniently be synthesized with liquid phase chemistry, covalently bonded semiconductors require higher synthesis temperatures. Over the past decade, nonthermal plasmas have emerged as capable synthetic approaches for the covalently bonded semiconductor nanocrystals. Among the main advantages of nanocrystal synthesis in plasmas is the unipolar electrical charging of nanocrystals that helps avoid or reduce particle agglomeration and the selective heating of nanoparticles immersed in low-pressure plasmas. This paper discusses the important fundamental mechanisms of nanocrystal formation in plasmas, reviews the range of synthesis approaches reported in the literature and discusses some of the potential applications of plasma-synthesized semiconductor nanocrystals.

The influence of hydrogen annealing on the morphology, microstructure and magnetic properties of CoPt films has been investigated. After changing the annealing environment from vacuum to hydrogen, the coercivity of the CoPt films increased from 610 to 2100 Oe at 500 °C. The more complete phase transformation may be attributed to the dissolution of hydrogen atoms in the interstitial sites of the CoPt lattice. Moreover, the size of the CoPt grains is smaller and the distribution is much more uniform in the hydrogen-annealed samples. The morphology change may be due to the existence of hydrogen atoms in the CoPt grain boundary which can inhibit the growth and coalescence of the CoPt grains.

Bottom pinned IrMn/[Co/Pt] multilayer films with relatively thin Pt layers (∼10 Å) grown on a Ta/Pt buffer have been found to exhibit favourable perpendicular exchange bias (PEB) and well-defined perpendicular anisotropy at room temperature. However, even the optimum film suffers from the same problem as those reported previously, i.e. the exchange bias field is just slightly larger than the coercivity. By replacing the Co layer in contact with IrMn by a 6–8 Å Co₆₀Fe₄₀ layer, the exchange bias is drastically enhanced while the large perpendicular anisotropy is sustained and the coercivity changes little. The exchange bias field for the IrMn/CoFe/[Pt/Co] films with sufficient high perpendicular anisotropy can reach a value as high as 950 Oe, which is almost three times the coercivity, and the corresponding unidirectional anisotropy, 0.22 erg cm⁻², considerably exceeds the best result at room temperature for various PEB systems ever reported. The present result suggests that PEB strongly depends on the composition of the ferromagnetic layer across the interface, which opens an effective avenue to boost PEB.

A micromagnetic model is performed to find the proper geometrical and magnetic parameters for current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin-valve heads at higher recording densities. The readout signals were studied versus the various height to width ratios for GMR sensors. When the GMR sensor width is reduced to 40 nm, the magnetization of the free layer rotates coherently in response to the excitation fields at various height to width ratios. In the calculated transfer curve of the GMR heads, the geometry and remanent M_rδ of the hard magnetic bias layers are optimized for the good performance characteristics of the head signal output. The imaging effects related to the narrow-gap shields are also investigated for the head design.

We report the observation of large exchange bias (EB) in Ni_50−xCo_xMn₃₈Sb₁₂ Heusler alloys with x = 0, 2, 3, 4, 5, which is attributed to the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) phases in the martensitic phase. The phase coexistence is possibly due to the supercooling of the high temperature FM phase and the predominant AFM component in the martensitic phase. The presence of EB is well supported by the observation of the training effect. The EB field increases with Co concentration. The maximum value of 480 Oe at T = 3 K is observed in x = 5 after field cooling in 50 kOe, which is almost double the highest value reported so far in any Heusler alloy system. Increase in the AFM coupling after Co substitution is found to be responsible for the increase in the EB.

We report on structural, magnetic and electronic properties of Co-implanted TiO₂(1 0 0) rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO₂ rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L₃ edge in the XAS spectra provides evidence that a sizeable portion of the dopants occupy substitutional Co²⁺ sites. The detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted TiO₂ plates. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the rutile phase, and the second one is a superparamagnetic phase which originates from the formation of metallic cobalt clusters in the implanted region. Using x-ray resonant magnetic scattering, the element specific magnetizations of cobalt, oxygen and titanium in Co-implanted TiO₂ single crystals are investigated. Magnetic dichroism was observed at the Co L_2,3 edges as well as at the O K edge. Anomalous Hall effect measurement indicates n-type carriers in Co-implanted TiO₂ rutile. The interaction mechanism, which leads to ferromagnetic ordering of substituted cobalt ions in the host matrix, is also discussed.

Different capping layers were deposited on 2.5 nm Co₇₂Fe₈B₂₀ to investigate their effects on damping constants and critical current density (J_C0) for spin-torque-transfer switching. The damping constant of CoFeB is affected by the interfacial conditions and the spin-pumping effects. The Cu capping layer significantly suppresses intermixing and possesses the lowest damping constant of 0.009. The micromagnetic simulations reveal that the low damping constant of CoFeB may result in the nucleation of domains at lower current density, and thus reduces J_C0. A reduction of 27% in J_C0 can be achieved by replacing the conventional Ta capping layer with a Cu layer.

We report here the magnetocaloric effect (MCE) in bulk and nanostructured gadolinium iron garnets (Gd₃Fe₅O₁₂). When compared with the bulk counterpart, the magnitude of the MCE is smaller for nanostructured samples with an average grain size of 50 nm, but increases when the grain size decreases to 35 nm. For the bulk sample, the MCE curves show a broad peak at 35 K; this peak is found to shift to lower temperatures for the nanostructured samples. The origin of the MCE peak for the bulk sample is associated with the intrinsic magnetic frustration and the ferromagnetic ordering of the Gd sublattice below 90 K, while for nanostructured garnets it is additionally ascribed to the surface spin disorder and particle blocking effects. While blocking is detrimental to achieving large MCE, surface spin disorder is found to enhance it under high applied fields.

The objective of this work is to study the magnetic properties of arrays of Ni–Fe nanowires electrodeposited in different template materials such as porous silicon, polycarbonate and alumina. Magnetic properties were studied as a function of template material, applied magnetic field (parallel and perpendicular) during deposition, wire length, as well as magnetic field orientation during measurement. The results show that the application of magnetic field during deposition strongly influences the c-axis preferred orientation growth of the Ni–Fe nanowires. The samples with magnetic field perpendicular to the template plane during deposition exhibit strong perpendicular anisotropy with greatly enhanced coercivity and squareness ratio, particularly in the Ni–Fe nanowires deposited in polycarbonate templates. In the case of polycarbonate template, as magnetic field during deposition increases, both coercivity and squareness ratio also increase. The wire length dependence was also measured for polycarbonate templates. As wire length increases, coercivity and squareness ratio decrease, saturation field increases. Such magnetic behaviour (dependence on template material, magnetic field, wire length) can be qualitatively explained by preferential growth phenomena, dipolar interactions among nanowires and perpendicular shape anisotropy in individual nanowires.

To combine the advantages of self-collimation, directional emission and co-directional coupling, a structure consisting of a self-collimation region, a coupler, a coupling section and two arbitrarily bent periodic dielectric waveguides is designed and analysed theoretically for optical interconnections. The light from the self-collimation region can be injected into the coupling section and transferred efficiently into the arbitrarily bent output branches if phase matching conditions are satisfied. By using the surface modification method, even when the Gaussian light source is placed far away from the self-collimation region, the desired directional emission effect can still be obtained. The performances of the proposed structure are evaluated by finite-difference time-domain simulations.

Charge transport in metal ion doped polyaniline has been studied by carrying out J–V and C–V measurements on metal–polyaniline junctions. Investigations show that the non-linear J–V characteristics cannot be explained on the basis of interfacial barrier alone. At high bias the J–V characteristics seem to follow space charge limited conduction with exponential distribution of traps. The barrier and trap parameters estimated from the measurements have been discussed.

We report on the device parameters of In_0.5Ga_0.5As/GaAs/Al_0.2Ga_0.8As quantum-dots- in-a-well infrared photodetectors annealed at various temperatures from 700 to 850 °C. The temperature dependent dark current–voltage characteristics are found to have a very weak dependence on the annealing temperature, revealing some interesting properties of the dark current mechanisms.

Here we present a simple and novel approach of fabricating three dimensional (3D) n-Si nanowires (NWs) and poly(3-octylthiophene) hybrid solar cells incorporating carbon nanotubes (CNTs). Vertically aligned n-Si NWs arrays were fabricated by electroless chemical etching of a n-Si [1 1 1] wafer. n-Si NWs/poly(3-octylthiophene) hybrid solar cells were fabricated with and without functionalized CNTs incorporation. Fabricated solar cells incorporating CNTs show open circuit voltage (V_oc), short circuit current density (J_sc) fill factor (FF) and conversion efficiency as 0.353, 7.85 mA cm⁻², 22% and 0.61%, respectively. In fabricated devices n-Si NWs arrays form multiple heterojunctions with the polymer and provide efficient electron collection and transportation, whereas CNTs provide efficient hole transportation.

An active volume scaling in the bore and length of a Sr atom laser excited in a nanosecond pulse longitudinal He–SrBr₂ discharge is carried out. The optimal temperature regime is found for laser oscillation on several different Sr atom and ion lines. The optimal discharge conditions for achieving a maximal multiline average output power are also found. At multiline operation a record average output power of 4.25 W is obtained, more than 90% of which is concentrated on the 6.45 µm Sr atom line. The radial distribution of the laser intensity is obtained experimentally to be a high-beam-quality Gaussian profile.

One-dimensional MgZnO nanostructures were grown directly on p-Si substrates by thermal evaporation at a variety of synthesis temperatures. Transmission electron microscopy and energy dispersive x-ray spectroscopy analysis revealed the formation of slim ZnO nanowires with twin boundaries on low Mg content nanosheets at lower synthesis temperatures, where the slim nanowires on the nanosheet did not have any detectable Mg content. The MgZnO nanostructures at elevated synthesis temperatures showed core/shell structures consisting of h-ZnO/h-MgZnO/c-MgZnO, where the h-MgZnO layer has a Mg content up to ∼9 at% and a further increase in Mg content in the outer shell induced the formation of the c-MgZnO phase. The ZnO nanorods covered with MgZnO layers showed enhanced band-edge emission due to the existence of a h-MgZnO barrier and a c-MgZnO dielectric layer.

We report organic thin-film transistors (OTFTs) made by simple solution processes in an ambient air environment. Inkjet-printed silver electrodes were used for bottom-gate and bottom-contacted source/drain electrodes. A spin-coated cross-linked poly(4-vinylphenol) (PVP) and a spin-coated 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as a gate dielectric layer and an active layer, respectively. A high-boiling-point solvent was used for TIPS-pentacene and the resulting film showed stem-like morphology. X-ray diffraction (XRD) measurement showed the spin-coated active layer was well crystallized, showing the (0 0 1) plane. The reasonable mobility, on/off ratio and threshold voltage of the fabricated device, which are comparable to those of the previously reported TIPS-pentacene OTFT with gold electrodes, show that the printed silver electrodes worked successfully as gate and source/drain electrodes. Furthermore, the device showed a subthreshold slope of 0.61 V/dec in the linear region (V_DS = −5 V), which is the lowest value for spin-coated TIPS-pentacene TFT ever reported, and much lower than that of the thermally evaporated pentacene OTFTs. It is thought that the surface energy of the PVP dielectric layer is well matched with that of a well-ordered TIPS-pentacene (0 0 1) surface when a high-boiling-point solvent and a low-temperature drying process are used, thereby making good interface properties, and showing higher performances than those for pentacene TFT with the same structure.

This paper reports the compositional dependence of the optical properties of vacuum evaporated amorphous Ge_xSe_80−xPb₂₀ films. The amorphous nature of the films was verified by their x-ray diffraction patterns. Various optical constants such as refractive index, extinction coefficient, refractive index dispersion parameters and optical band gap have been determined by analysing optical transmittance data in the wavelength range of 300–1600 nm. These parameters were found to exhibit a remarkable change at 20 at% Ge. The observed variation in the optical properties has been correlated with the formation of Ge–Se structural units at the expense of Se–Se units. The change in optical constants and dispersion parameters with Ge content in place of Se has been ascribed to the corresponding change in the net polarizability of the system. However, variation in the optical bandgap was interpreted on the basis of removal of structural defects with Ge addition. The dispersion energy has also been estimated using the single oscillator model to determine the coordination number and the static refractive index.

Zn_1−xV_xO films (x = 0, 1.3, 1.9, 2.6, 3.5, 4.3 and 6.2 at%) were prepared on glass substrates via the direct current reactive magnetron co-sputtering method. The microstructure, band gap, photoluminescence and Raman scattering of these films have been systematically investigated. The structural and chemical state characterizations indicate that the crystallinity of Zn_1−xV_xO films (x ⩽ 2.6 at%) can be improved by V incorporation into the ZnO wurtzite lattice, but excess V will precipitate as V clusters when x ⩾ 4.3 at%, resulting in the deterioration of crystal quality. The defects in Zn_1−xV_xO films (x ⩽ 2.6 at%) can be suppressed by V doping, which induces the enhancement of the near band edge (NBE) emission. However, when x ⩾ 4.3 at%, defects adjacent to the V dopant quench the NBE emission. On the other hand, the band gap of the films gradually increases with the increase in V concentration, which is accompanied by the blue shift of the NBE emission.

The evolution of novel procedures for the evaluation of equivalent dose using the optically stimulated luminescence (OSL) signal of quartz became necessary to address (i) the sensitization experienced by the signal during the pre-heat treatment and (ii) the in situ sensitization occurring in nature. The pre-dose phenomena of the OSL and 110 °C TL pre-dose emissions have been reported to be similar. In light of this observation, an attempt has been made in this paper to visualize the role of R-centres in the sensitization process of the OSL emission. The results, based on the experimental observations and kinetics considerations of R-centres, confirm that the R-centres participate in the sensitization process of this signal.

The paper demonstrates the selective bulk synthesis of few-layer graphenes by optimizing an external magnetic field assisted electric arc. An ultra-high purity glassy graphite anode was sublimated in an argon atmosphere, and carbon nanotubes (CNTs), along with graphene sheets, were found inside the deposit formed on the cathode. Both the high purity CNTs and the graphene sheets, with minimal structural defects, were synthesized separately by varying the strength and orientation of the external magnetic field. The as-synthesized carbonaceous samples were characterized with the help of transmission electron microscopy, selected area electron diffraction (SAED), Raman spectroscopy and thermogravimetry with the objective of optimizing the highest selective production of 2D graphene structures. The as-synthesized graphene sheets exhibited a relatively high degree of graphitization and low structural defect density as confirmed by Raman spectroscopy. They were found to exhibit higher oxidation temperature (767 °C) than that of the carbon nanocrystalline particles (690 °C), as inferred from the thermogravimatric analysis. Moreover, they were found to roll up at their edges on account of their surface energy minimization. This was confirmed by the SAED analysis. With this new technique, we could successfully synthesize 2D graphene structures at the rate of a few g h⁻¹.

This paper reports on first systematic investigations into the dynamics of a self-sustained volume discharge (SSVD) in SF₆-based mixtures pre-irradiated by a pulse CO₂ laser. Two different illumination geometries are considered, one with a diaphragm slit arranged normal to the central electric field line of the discharge gap and the other with the discharge gap being wholly irradiated. The pattern of a laser-induced gas dynamic disturbance has been theoretically drawn starting from a shock wave theory and visualized by taking SSVD photographs. The delay times between the laser and voltage applications were varied from a few to several tens of microseconds. It has allowed us for the first time to obtain information, based on measuring the discharge voltage, about how long the mixtures considered are capable of being exposed to high temperature with no dissociation. The dynamic barrier effect found in our previous works is thoroughly investigated in both illumination geometries and the observed discharge patterns are qualitatively treated in terms of the electric field distortion by the surface charges at the shock wave fronts. The corresponding surface charge density is numerically estimated. The concept of controlling the electric field distribution over the discharge gap using the dynamic barrier effect is put forward.

Experimental results of time-resolved optical emission intensities of atomic neon lines (585.2 and 640.2 nm) in a pulsed, low pressure (10–95 mTorr) inductively coupled afterglow neon plasma are presented. It is found that the light intensity at 585.2 nm decays exponentially but at 640.2 nm shows a typical bi-exponential decay after the rf power is turned off. Since the population of these two excited levels is generated by inelastic collisions between electrons and atomic neon (1s₅ metastable and ground state), the evolution of these two emission lines can also be estimated by a simple collisional–radiative (CR) model which uses time-dependent results of EEPF and the concentration of 1s₅ atoms, both of which can be measured by using optical absorption techniques and a Langmuir probe. It is found that the measured evolution of the emission intensity at 640.2 nm has an excellent agreement with that from the model, over a long time interval after the rf power is turned off (from 20 to 150 µs), as long as the measured EEPF is used instead of an assumed Maxwellian.

High power pulsed magnetron sputtering is used for the growth of titanium dioxide (TiO₂) films at different working pressures and orientations of the substrate with respect to the target surface. In the case of substrates oriented parallel to the target surface, the increase in the working pressure from 0.5 to 3 Pa results in the growth of crystalline TiO₂ films with phase compositions ranging from rutile to anatase/rutile mixtures. When depositions are performed on substrates placed perpendicularly to the target surface, rutile films that consist of TiO₂ nanocrystals embedded in an amorphous matrix are obtained at 0.5 Pa. Increase in the working pressure leads to the deposition of amorphous films. These findings are discussed in the light of the energetic bombardment provided to the growing film at the various deposition conditions.

Tungsten–inert-gas welding arcs are modelled using a two-dimensional axisymmetric computational code. Both electrodes (the tungsten cathode and the metal anode workpiece) and the arc plasma are included self-consistently in the computational domain. The influence of adding helium, hydrogen and nitrogen to the argon shielding gas is investigated. It is found that addition of any of the gases increases the heat flow to and the current density at the anode. The shear stress and the arc pressure at the anode surface are increased by adding hydrogen or nitrogen or up to about 50 mol% helium, but decrease when more helium is added. It is predicted that the effect of adding any of the gases is to increase the depth of the weld pool, in agreement with the experimental evidence. The results are explained by referring to the thermodynamic and transport properties of the gas mixtures.

Inductively coupled SF₆/SiCl₄ plasmas interacting with a bulk silicon substrate and a SiO₂-coated substrate have been investigated. Mass spectrometry and optical emission spectroscopy diagnostics were used to characterize the neutral population in the diffusion chamber. SiF₄ molecules were detected as the dominant species, and their formation has been attributed to the high reactivity of F radicals with SiCl_x species. In a complementary experiment, a silicon chloride layer was deposited on the reactor walls during a SiCl₄ plasma step and subsequently etched by a SF₆ plasma. Time-resolved measurements of the neutral densities during the SF₆ plasma step showed the importance of heterogeneous reactions between impinging F radicals and SiCl_x species deposited on the reactor walls. In SF₆/SiCl₄ plasmas, these reactions lead to a depletion in F radicals, which results in a decrease in the silicon substrate etch rate. Furthermore, this impacts on the concentration of SF_x species and on the creation of new species, such as ClF, SF₅Cl and S₂Cl₂.

The interaction of gold with CeO₂ layers was investigated using photoelectron spectroscopy. 65 nm thick Au doped CeO₂ layers were deposited by rf-magnetron sputtering on a Si(0 0 1) substrate by using a composite CeO₂–Au target. The laboratory XPS and synchrotron radiation soft x-ray and hard x-ray photoemission spectra showed the formation of stoichiometric Ce⁴⁺ (CeO₂) and the appearance of new Au^+,3+ states with ionized Au species in excess of 50% of the total Au amount. Depth resolved measurements, by varying the emission angle or photon energy, indicated the formation of an Au⁰ overlayer and deeper Au^+,3+ species. The formation of Au^+,3+ ions was found to be strongly dependent on the cerium oxide stoichiometry. The amount of ionized Au can be reversibly decreased and increased by surface reduction (removal of O by sputtering) and subsequent surface re-oxidation.

This paper presents an experimental and computational study of semiconductor–insulator–semiconductor (SIS) tunnel solar cells. A transparent and conductive film of thallium trioxide Tl₂O₃ has been deposited by anodic oxidation onto an n-Si(1 0 0) face to realize the SIS tunnel solar cells based on Si/SiO_x/Tl₂O₃. An efficiency of 8.77% has been obtained under an incident power density of 33 mW cm⁻² illumination condition. A PSPICE model is implemented. The calculated results show that the theoretical values are in good agreement with experimental data. Moreover, the simulation clearly demonstrates that the performance of the tested device can be significantly improved.

The development of a UV reflection anisotropy spectrometer has extended the current range of the reflection anisotropy spectrometry (RAS) technique to 7.0 eV. The extra range has been used to obtain the RAS of the Au(1 1 0)/electrolyte interface to 7.0 eV. The RA spectrum obtained for this interface is significantly different in the range 4.6 to 5.5 eV from the results obtained with the conventional instrument.

The effects of a laser field on the conduction-electron effective Landé g factor in GaAs–Ga_1−xAl_xAs quantum wells and quantum-well wires under applied magnetic fields are studied within the effective-mass approximation. The interaction between the laser field and the semiconductor heterostructure is taken into account via a renormalization of the semiconductor energy gap and conduction-electron effective mass. Calculations are performed for the conduction-electron Landé factor and g-factor anisotropy by considering the non-parabolicity and anisotropy of the conduction band. Theoretical results are obtained as functions of the laser intensity, detuning and geometrical parameters of the low-dimensional semiconductor heterostructures, and indicate the possibility of manipulating and tuning the conduction-electron g factor in heterostructures by changing the detuning and laser-field intensity.

In this study the synthesis of nanocrystalline zinc oxide powders using an oxidative electrodeposition method without the use of any surfactants or stabilizers was explored. Nanocrystalline zinc oxide powders were successfully produced by this method and characterized and the effect of the process parameters was studied. The experimental results and analyses were validated against a proposed mechanism for particle formation during oxidative electrodeposition. It was demonstrated that the proposed mechanism can describe the process accurately.

Thin films of zinc ferrite (ZnFe₂O₄) were deposited on glass substrates at room temperature in pure argon and pure oxygen environments by RF-magnetron sputtering. The structural and optical properties of the films were studied as a function of pure O₂ pressure using an RF power of 100 W. The XRD data show the film having a spinel structure. The AFM images show the nanocrystalline nature of the films. The particle size depends on the environment and varies between 55 and 75 nm. The smaller value is obtained for the film deposited under the pure argon environment. The optical constants of the films were extracted from the transmission spectra by the envelope method. The estimated direct energy band gap values for the film deposited at 8 mTorr of gas pressure in pure Ar is 2.43 eV. For the films deposited in pure O₂, the band gap increases from 2.48 to 2.61 eV as the O₂ pressure is increased from 8 to 31 mTorr. The dispersion of the refractive index (n) is discussed in terms of the single-oscillator Wemple–DiDomenico model. This model is also used to estimate the dispersion parameters and the static refractive index.

A novel technique for experimental estimation of the correlation length of insulator thickness fluctuations is proposed which is based on the statistical treatment of the results of current measurements for a random set of thin metal–insulator–semiconductor (MIS) capacitors. For testing purposes, the usual Al/SiO₂/Si tunnel diodes with excessive thickness dispersion, as well as the less popular but potentially interesting Au/CaF₂/Si structures, are taken. The verification is performed by a direct comparison of correlation lengths yielded by the new method with those obtained by diagnostics of the same dielectric films using atomic force microscopy.

AlCrNbSiTiV nitride films were deposited by reactive radio-frequency magnetron sputtering and the effects of substrate bias on the chemical composition, structure and mechanical properties of the deposited films were investigated. AlCrNbSiTiV nitride films exhibit a single FCC NaCl-type structure and have the stoichiometric nitride ratio of (Al, Cr, Nb, Si, Ti, V)₅₀N₅₀. The deposition rate decreases with increasing substrate bias due to resputtering effects and densification of films, which also leads to less obvious columnar structure, reduced grain size, smaller surface roughness and transition of preferred orientation from the (1 1 1) plane to the (2 0 0) plane. The nitride film deposited at −100 V exhibits the maximum compressive stress around 4.5 GPa and attains a peak hardness and an elastic modulus of 42 GPa and 350 GPa, respectively, which fall in the superhard grade. Moreover, the film keeps its hardness at the superhard grade even after its residual compressive stress was partially released by annealing at 1073 K for 5 h. The structural evolution mechanism and strengthening mechanism are both discussed.

Swift heavy ion (SHI) irradiation of amorphous Si (a-Si) at non-perpendicular incidence leads to non-saturable plastic flow. The positive direction of flow suggests that a liquid phase of similar density to that of the amorphous solid must exist and accordingly a-Si behaves like a conventional glass under SHI irradiation. For room-temperature irradiation of a-Si, plastic flow is accompanied by swelling due to the formation of voids and a porous structure. For this paper, we have investigated the influence of SHI irradiation at room temperature on amorphous Ge (a-Ge), the latter produced by ion implantation of crystalline Ge substrates. Like a-Si, positive plastic flow is apparent, demonstrating that liquid polymorphism is common to these two semiconductors. Porosity is also observed, again confined to the amorphous phase and the result of electronic energy deposition. Enhanced plastic flow coupled with a volume expansion is clearly responsible for the structural modification of both a-Si and a-Ge irradiated at room temperature with swift heavy ions.

Using first-principles calculations, we investigate the electronic structure of CoSb₃ compound by considering the spin–orbit interaction. Within the framework of Boltzmann theory, the transport coefficient (power factor) is evaluated as a function of chemical potential assuming a rigid-band picture and constant relaxation time. It is found that appropriate n-type doping in the compound may be better than p-type doping to enhance the power factor. Our theoretical calculations give a plausible guide on how to optimize the thermoelectric performance of this compound, and the upper limit of its ZT value is estimated.

This report investigates the effect of the dielectric layer thickness on both magnetic and electric resonances of cut-wire-pair (CWP) structures in the microwave frequency regime. It was found that the resonances are sensitive to the thickness of the dielectric layer. As the thickness increases, the bandwidth of the magnetic resonance is slightly extended to a higher frequency, while the low-frequency edge of the electric-resonance band is remarkably shifted to a lower frequency. It was also found that the dependence of the magnetic resonance frequency on the dielectric layer thickness follows the trend of the closed formula based on the cavity model for the coupled metallic elements (Cai et al 2007 Opt. Express15 3333). In addition, we also studied the effect of the dielectric layer thickness on the left-handed behaviour of a combined structure consisting of CWP and continuous wire. The actual measurements are compared with the numerical simulation values to show a good coincidence.

Nanoindentation creep of nanocrystalline Ni with the as-deposited grain size of 14 nm was characterized at elevated temperatures. The indentation creep rate was observed to scale with temperature and applied load, and could be expressed by an empirical equation used for describing power-law creep in conventional crystalline solids. Creep activation energy was found to be close to that for the grain boundary self-diffusion of Ni. The activation volume was also measured using a stress relaxation technique. The current creep results were directly compared with those from fine-structured Ni in the literature. Possible creep mechanisms, such as diffusional creep, grain boundary sliding, power-law and power-law breakdown, were discussed in light of the creep rate and temperature ranges.

The aim of this study was the development and characterization of transition metal oxynitride multilayers for optical applications. The reactive RF magnetron sputtering technique in rotation mode was used for stacking of zirconium oxynitride (ZrNO) and titanium oxynitride (TiNO) nanolayers. The depositions were carried out in a reactive Ar+N₂+O₂ atmosphere by sputtering titanium and zirconium targets. By means of different substrate rotation speeds, the bilayer period has been changed in the range 11–20 nm. A multilayer deposition rate increasing with the bilayer period decreasing has been evaluated. Structural, compositional, mechanical and optical analyses have been performed. The x-ray diffraction spectra confirmed the formation of a multilayer structure with a nitride formation prevalence. Non-abrupt interfaces between the layers and non-uniform chemical composition (chemical intermixing) have been detected by transmission electron microscope (TEM) observations. The gradient interface structure turns out to be an advantage for the improvement of the mechanical properties. Higher hardness values were calculated by the Chicot–Lesage and Jonsson–Hogmark models for TiNO/ZrNO multilayer compared with monolayer TiNO and ZrNO coatings. Also SIMS analysis has confirmed a compositional interface grading but also an increase in oxygen content with decreasing substrate rotation speed or similarly with decreasing deposition rate. Moreover, a tuning of the optical properties, going from metallic behaviour to dielectric with the decrease in the substrate rotation speed has been gained. The variation of the deposition rate allows a sort of 'regulation' of the oxygen incorporation with a precise tailoring of the optical properties. This result can be employed with the aim of depositing graded composition multilayer systems with a precise control of their optical selective wavelength properties. The improvement in the mechanical performance in graded oxynitride multilayer coatings would also allow an increase in the optical device lifetime.

We investigated the electronic properties of thermally oxidized Ni films using the optical spectroscopic technique and found that the optical properties of the NiO films exhibit systematic changes with oxidation degree in accord with structural and magnetic analysis results. We discuss our findings in relation to the doping to a Mott insulator and the inhomogeneous phase of a Ni(metal)–NiO(insulator) nano-composite.

A thin film of the ternary Ga₁₀Ge₁₀Te₈₀ compound has been deposited at room temperature on a Corning 7059 glass substrate by the e-beam evaporation technique at vacuum pressure ∼1.8 × 10⁻³ Pa. X-ray diffraction studies revealed that the as-deposited films and those annealed up to 400 K have an amorphous phase, while those annealed at 450 K are crystalline. The elemental chemical composition of the as-deposited films was confirmed using energy dispersive x-ray analysis. The transmission and reflection spectra of the as-deposited and annealed films at annealing temperature 450 K were recorded at normal light incidence in the wavelength range 600–2500 nm. The refractive index and optical band gap have been calculated for the investigated films. The dispersion parameters, (E_o, E_d), static refractive index, n_s(0), static dielectric constant, ε_s, and the carrier concentration to the effective mass ratio, N/m^*, have been calculated. An analysis of the optical absorption spectra revealed an indirect optical transition characterizing the as-deposited films while direct and indirect optical transitions characterized the films annealed at 450 K.

Ce-doped Bi_1−xCe_xFeO₃ (BCFO_x) thin films with x = 0–0.12 were successfully prepared on SnO₂ : F(FTO)/glass substrates by chemical solution deposition. The BCFO_x films showed a gradual phase transition from a rhombohedral to a pseudotetragonal structure with increase in the Ce content. The substitution of Bi with Ce greatly reduced the leakage current and the dielectric loss of the BCFO_x films, which showed an Ohmic conduction mechanism. The BCFO_x films with x = 0.06 exhibited a well squared-shaped P–E hysteresis loop with a remanent polarization (2P_r) of 92.3 µC cm⁻² and an improved anti-fatigue characteristic after 10¹⁰ read/write polarization cycles.

Nanostructured NdFeB hard magnetic material exhibiting enhanced magnetic properties can be produced by direct chill or melt spinning followed by recrystallization. The surface condition and nanostructure of stoichiometric, Fe_82.3Nd_11.8B_5.9, and near stoichiometric, Fe_83.2Nd_10.9B_5.9, alloy ribbons and the effect of melt-spinning parameters on the structure are investigated using optical, scanning and transmission electron microscopes. The formation of gas pockets on the roll surface of the ribbons during melt spinning can prevent heat transfer which can result in local coarse grains. A decrease in the ribbon thickness and mean Nd₂Fe₁₄B grain size and improvement in magnetic properties, including remanence enhancement, were observed on increasing the roll speed, prior to vitrification and consequent collapse of properties at higher speeds. An orientation relationship was found between the Nd₂Fe₁₄B and α-Fe phases for coarse grain samples melt spun at low roll speeds. Dark field TEM also showed that some of the α-Fe precipitates had identical orientations showing epitaxy with the Nd₂Fe₁₄B matrix phase. A preferred growth orientation of [0 0 1] was observed for some Nd₂Fe₁₄B grains.

Quasi-arrayed ZnMgO single-crystal nanorods with different Mg concentrations have been fabricated by thermal evaporation of Zn and Mg on a Si substrate using Au as a catalyst. The synthesized ZnMgO nanorods had uniform flat hexagonal crystallorgraphic planes with diameters of about 300 nm. It was found that with the increase in the dopant concentration, the peak position of (0 0 2) was shifted towards the high-angle side (from 34.40° to 34. 54°) and the near-band-edge emission was blue-shifted to 364 nm (3.41 eV) from 385 nm (3.22 eV) in comparison with that of pure ZnO. The direct modulation of the band-gap caused by Mg substitution was responsible for the blue shift. The possible growth mechanism of the ZnMgO nanorods was discussed.

Using the technique of picosecond acoustics, we measure the basic elastic and optical properties of a micrometre-thickness zinc-blende (cubic) GaN epitaxial film grown on GaAs. We provide low temperature values of the speed of sound, c₁₁ elastic constant and refractive index. Our value of the elastic constant is in good agreement with the theoretical calculations for cubic GaN (Wright 1997 J. Appl. Phys.82 2833).

A high sensitivity and large dynamic range are observed in LiNbO₃ : Fe : Cu and In-doped LiNbO₃ : Fe : Cu crystals at 488 nm wavelength based on the two-beam coupling experiment. The strong blue photorefraction is contributed by the two-centre effect and the remarkable characteristic of being in phase between the two gratings recorded in shallow and deep trap centres. The sensitivity S is measured up to 6.24 cm J⁻¹, and simultaneously the dynamic range M/# is achieved to 34.2 in the In-doped LiNbO₃ : Fe : Cu crystal, which are enhanced significantly as compared with those of the LiNbO₃ : Fe : Cu crystal under the same experimental conditions. The damage-resistant dopants such as In³⁺ ions are no longer damage resistant, but they enhance the photorefractive properties at 488 nm wavelength. Experimental results definitely show that In-doped two-centre LiNbO₃ : Fe : Cu crystal is a promising candidate as a blue photorefraction material for volume holographic storage.

Carbon inverse opals (CIOs) are fabricated by a replica method using synthetic opals formed by the sedimentation of SiO₂ spheres as a template. The pore size of the CIOs is determined by the diameter of the SiO₂ spheres. These periodic structures of carbon exhibit field emission (FE) characteristics. The main emission sites of CIOs are interpreted to be the sharp edge of triangular prisms formed along the boundary of the neighbouring pores. The FE characteristics improved upon heat treatment at high temperature, in cases where the pore structure was not deformed. The graphitization of the carbon and the shrinking of the pore structure led to an improvement of the FE characteristics. On the other hand, the deformation of the pore structure prevents the FE characteristics from improving.

The ground state properties of three compounds, Cr₇C₃, Fe₃C and Fe₂B, are investigated using ab initio calculations based on density functional theory. Formation enthalpy values indicate that Cr₇C₃ is the most stable crystal among the three compounds. Fe₃C is metastable which has a positive heat of formation value. The calculated bulk modulus, shear modulus and Young's modulus value of Cr₇C₃ are 311 GPa, 143.8 GPa and 374 GPa, respectively. The bulk modulus values of Fe₂B and Fe₃C are 194 GPa and 258 GPa. We also find that both the hardness and the stiffness of the Cr₇C₃ type carbides can be improved by doping with B, W, Mo, etc. The bulk modulus of transition metal doped Fe₂B is considerably higher than pure Fe₂B. The electronic structures of Fe₂B and Fe₃C are ferromagnetic and the evaluated average magnetic moment of Fe is 2.09μ_B/atom for Fe₃C and 2.02μ_B/atom for Fe₂B, respectively. Micro-indentation test results indicate that Cr₇C₃ is the hardest phase among the three phases and shows excellent wear resistance performance under three-body abrasive experiments. The experimental results are in agreement with the theoretical prediction that Cr₇C₃ is the best both in stability and mechanical performance.

This paper describes the structure of Er³⁺-doped SiO₂–HfO₂ waveguides containing nanocrystals of HfO₂. Pure and 1 mol% Er³⁺-doped 70SiO₂–30HfO₂ films were deposited by the sol–gel method on amorphous SiO₂ substrates using the dip-coating technique. Each waveguide has experienced a single thermal treatment at temperatures ranging from 900 to 1200 °C, for either short (30 min) or long (24 h) durations. Crystallization and microstructure were studied by x-ray diffraction (XRD). The local environments of hafnium and erbium ions were determined, respectively, from Hf and Er L₃-edges extended x-ray absorption fine structure (EXAFS) experiments. Both XRD and EXAFS results demonstrate the substitution of Hf⁴⁺ by Er³⁺ ions in the crystalline structure. XRD shows the nucleation of tetragonal HfO₂ nanocrystals after heat treatment at 1000 °C for 30 min in the pure waveguide, and at 900 °C for 24 h in the waveguide doped with Er³⁺. In both series, partial transformation from tetragonal to monoclinic HfO₂ nanocrystals starts after heat treatment at 1100 °C for 24 h. The average crystallite size and size distribution can be controlled by thermal annealing temperature and duration, respectively, with brief treatment yielding a more homogeneous nanocrystal size.

The phase constant surfaces of two-dimensional phononic crystals consisting of steel cylinders in water are calculated to predict the directivity of acoustic wave propagation. A highly directional acoustic source can be obtained at a pass band frequency far away from the band edge states. This observation is quite different from those in the two former approaches, where one is due to the high density of band-edge states and the other is due to the resonant cavity state in two-dimensional phononic crystals. The prediction is validated by the acoustic field distributions of a finite structure with 24 × 24 unit cells.

Positron annihilation spectroscopy was used to depth profile the modification of intrinsic structural nanovoids in silica glass implanted with Ar⁺ ions at different fluences and implantation energies. Beyond an expected defect distribution below the ion projected range R_p, a second defect distribution extending more than two times deeper than R_p was revealed. This second defective layer was found to be related to recoiled oxygen atoms whose diffusion is probably increased by the stress gradient induced by the compaction of the first layer.

MoO₃ thin films were successfully prepared through chemical vapour transport (CVT) deposition and post-annealing. These films showed significantly improved optical properties. It was found that the transmittance reaches 80% with low reflectivity due to improved crystallinity and removal of oxygen vacancy states. Optical analysis shows that the index of refraction is around 1.55 with a flat dispersion curve across the visible. Furthermore, the band-gap energy is estimated to be approximately 3.5 eV. These properties suggest that CVT may be an effective thin film deposition technique for low-cost, large-area deposition of molybdenum oxides for chromogenic applications.

Composite metamaterials (CMMs) combining a subwavelength metallic hole array (i.e. one-layer fishnet structure) and an array of split-ring resonators (SRRs) on the same board are fabricated with gold films on a silicon wafer. Transmission measurements of the CMMs in the terahertz range have been performed. Dual-band magnetic resonances, namely, an LC resonance at 4.40 THz and an additional magnetic resonance at 8.64 THz originating from the antiparallel current in wire pairs in the CMMs, are observed when the electrical field polarization of the incident light is parallel to the gap of the component SRR. The numerical simulations agree well with the experimental results and further clarify the nature of the dual-band magnetic resonances.

In this paper, the contribution of the domain walls motion to the dielectric and piezoelectric responses for the 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ system is investigated. A monotonically increasing temperature dependence of the dielectric permittivity is observed from very low temperatures up to the ferroelectric–paraelectric phase transition temperature. It is verified that the major contribution to dielectric response at room temperature is from the extrinsic effect. A linear dependence of the permittivity with the amplitude of the ac applied electric field is verified from the nonlinear dielectric measurement. Rayleigh's model is used to quantitatively evaluate the dielectric response, leading to similar behaviour of the typical soft PZT. On the other hand, direct piezoelectric response also displays a Rayleigh-type behaviour. Piezoelectric measurements show in the entire investigated dynamic stress range a decrease in the piezoelectric response with both increase in frequency of the applied dynamic stress and increase in the pre-stress on the samples.

We have studied the influence of Al incorporation in the crystalline structure of ZrN thin films deposited by dc magnetron sputtering at low temperature. The amount of aluminium in the films depends directly on the power applied to the aluminium cathode during the deposition. Energy dispersive x-ray analysis and x-ray diffraction (XRD) were used to obtain the chemical composition and crystalline structure of the films, respectively. When Al atoms are incorporated into the ZrN coatings, the strong ZrN (2 0 0) orientation is modified by a combination of other ones such as ZrN (1 1 1), Zr₃N₄ (2 1 1) and hexagonal AlN (1 0 0) as detected from the XRD spectra for high aluminium concentrations. Fourier-transform infrared spectroscopy allowed us to identify oxides and nitrides, ZrO, AlO and AlN, incorporated into the deposited films. The effect of a bias voltage applied to the substrate has also been investigated and related to the changes in the microstructure and in the nanohardness values of the ZrAlN films.

Penetration depth fluctuations of single-mode fibre laser welds made with long focal length optics and the effects of sinusoidal laser power modulations were studied. It was found that the welds had a high aspect ratio and were subject to spiking defects. The magnitude of the penetration fluctuations tended to be larger for deeper welds. The weld penetration profiles had positive maximal Lyapunov exponents and broadband, aperiodic power spectral densities with most of the signal power in the spectral band from 0 Hz to 1 kHz. The amplitude of the frequency response of the laser penetration to large amplitude laser power modulations decreased at rates varying from −20 to −60 dB decade⁻¹ at modulation frequencies from 100 Hz to 1 kHz. It was found that sinusoidal laser power modulation at frequencies from 900 Hz to 3 kHz decreased the aperiodic penetration fluctuations.

The effect of liquid properties on gas bubble growth and motion characteristics in liquid films confined within a nanogap between a highly polished steel ball and a smooth glass disc under an electric field is reported. Experimental results show that the critical voltage for the appearance of bubbles has insignificant dependence on liquid viscosity and surface tension. The bubble size after detachment increases with liquid viscosity, and bubble instability and coalescence tend to occur when bubbles move some distance away from where they were formed. An increase in liquid surface tension results in larger bubbles at the growth stage. Also, the bubble motion characteristics are greatly influenced by liquid viscosity, and the dielectrophoresis force is demonstrated to be the dominant driving force for bubble movement. Theoretical models and analyses have been used to discuss the bubble formation and describe the bubble movement characteristics.

A method is proposed to fabricate conductive patterns and tracks on large area flexible substrates using a UV roll imprinting lithography process. A durable metal roll stamp, which is extendable to mass production, was fabricated by using a series of photolithography, electroforming and anti-adhesion coating processes. Indium tin oxide (ITO) conductive patterns and tracks with line widths of 2–20 µm were formed by using the UV roll imprinting process and a subsequent etching process. The geometrical properties and electrical conductivity of fabricated ITO patterns and tracks were measured and analysed.

The thermo-stability of acrylate based holographic polymer dispersed liquid crystal gratings has been evaluated with regard to their morphology, diffraction efficiency, Bragg angle and electro-optical tunable performance. Our studies indicate that the thermo-stability is closely related to the chemical structure of the monomers in the grating. Usually, a more rigid molecular structure forms a more stable morphology. Another important aspect, the reaction efficiency of the system, shows that a highly efficient photoreaction leads to a dense polymer network and high ene-conversion, thus promoting the phase separation of the liquid crystal and enhancing the thermo-stability. We also find that a higher average functionality of the monomers can improve grating thermo-stability due to denser crosslinked polymers and more complete phase separation.

We examine the theoretical basis for the enhancement of classical, dielectric actuation by first imposing an elongation ('pre-strain') in one of the two directions in the plane of the working elastomeric filling between flexible electrodes. Such anisotropic actuation has been shown experimentally to be effective in delivering more mechanical work from a given applied voltage. A wrinkling instability in the in-plane direction perpendicular to the load limits the applicability of this strategy. It is shown to intervene before pull-in.

This recently published paper contains an incorrect image for figure 1(g) on page 3 which should be replaced by the figure below. Other images in figure 1, as well as the caption and discussions about figure 1, are correct.

Figure 8. SEM images of Ag films deposited on bulk ZnO (0 0 0 1) surfaces at (a)–(d) 300K and (e)–(h) 140 K. The average thicknesses are (a), (e) 7 nm, (b), ( f ) 14 nm, (c) (g) 25 nm and (d), (h) 35 nm.