Rare-earth (RE) doped III-nitrides, prepared by in-situ doping during growth or by ion implantation and annealing, are promising materials for visible light emitting displays. In addition, they are extremely challenging theoretically, on account of the complexity of the sharp inter-4f optical transitions, which are allowed only through the mixing by non-centrosymmetric crystal fields of the inner 4f orbitals with higher-lying states of opposite parity. We review recent experimental and theoretical work on Er-, Eu- and Tm-doped III-nitride compounds and alloys which has been carried out with a view to establishing the lattice location of RE in these materials and the probable nanostructure of the centres which are responsible for their luminescence. The isolated site REIII is found to be both optically and electrically inactive, but in association with neighbouring intrinsic defects (most probably nitrogen vacancies) REIII can generate a small family of similar optically active sites. Such a family is held to be responsible for the site multiplicity that is a common feature of the spectroscopy of RE-doped III-nitrides.

We have explored the effects of 120 MeV Si9+ ion beam irradiation on the electrical, structural and capacitance properties of HClO4 doped polyaniline conducting polymer electrodes. The swift heavy ion (SHI) irradiated conducting polymer films exhibited upto 70% increase in crystallinity and dc conductivity with improved surface morphology. The supercapacitors fabricated with ion irradiated polyaniline electrodes showed enhancement of electrochemical stability and slight decrease in internal resistance, which could be attributed to the removal or stabilization of the volatile surface groups and decrease in surface roughness upon ion irradiation. Fluence dependent small increase in coulombic efficiency is observed in the supercapacitors with SHI irradiated polymer electrodes because of the increase in dc conductivity of the polymer electrodes upon irradiation.

In order to study the preferred crystal orientations of Mg-Zr-O composite protective layers in PDP, Mg-Zr-O composite protective layers were deposited by Electron-beam Evaporator using (MgO+ZrO2) powder mixture as evaporation source material. X-ray diffractometer (XRD) was used to determine preferred crystal orientations of Mg-Zr-O composite protective layers, surface morphologies of films were analyzed by FESEM and voltage characteristics were examined in a testing macroscopic discharge cell of AC-PDP. On the basis of experimental analysis, the influence of oxide addition and deposition conditions on preferred orientations of Mg-Zr-O composite protective layers were investigated. The results showed that the preferred orientations of Mg-Zr-O films were determined by lattice distortion of MgO crystal. The deposition conditions have great effects on the preferred orientations of Mg-Zr-O films. The preferred orientations affect voltage characteristics through affecting surface morphology of Mg-Zr-O films. A small amount of Zr solution in MgO can decrease firing voltage compared with using pure MgO film. Firing voltage is closely related with the [ ZrO2/(MgO+ZrO2)] ratio of evaporation source materials.

Reactively evaporated thin films of tantalum oxide are prepared on glass substrate, using electron beam heating, for optical applications. Firstly, the deposition was carried out at 0.20 nm/s, with substrate temperature of 200 °C, and oxygen flow rate was varied from 0.0 to 30.0 sccm to study the effect of flow rate on optical constants. The optical constants evaluated by using transmission data of the samples, with curve fitting, show a strong dependence on oxygen flow rate. Oxygen flow rate of 10.0 sccm has been found to give reasonably high index (n:2.11 at $\lambda =500$ nm) and low absorption of the order of 10−3 in most part of the desired spectrum (380–850 nm). However, for oxygen flow rates below 10.0 sccm and above 20.0 sccm the films have exhibited low index and comparatively high absorption. In the next step, deposition rates were varied from 0.10–0.30 nm/s with steps of 0.01, keeping oxygen flow rate and substrate temperature constant at 10.0 sccm and 200 °C respectively, to optimize the film properties. A variation in refractive index and extinction coefficient values is observed with varying deposition rates. An increase in refractive index (n:2.125 at $\lambda =500$ nm) with reduced absorption (“k” of the order of 10−4) is achieved over the entire spectrum for the film deposited at 0.10 nm/s. The film was found to be highly adherent to the substrate as revealed by qualitative adhesive tape peel test. Keeping in view the application of the work, calculation of optical constants was extended up to 1100 nm for the sample deposited at 0.10 nm/s. The results have shown nearly constant optical constant values over the extended range making the film useful over a broad spectral region. AFM studies show that the surface is extremely smooth and compact, giving average and rms roughness values of 5.51 and 7.174 Å respectively, for the studied area of $2.5~\mu \times2.5~\mu$. XRD and SEM studies carried out for structural analysis show that the film is generally amorphous with a sign that crystalline structure could be achieved at little higher substrate temperatures. The surface of the film is very smooth, free of voids, with the particle size in the range of 17–35 nm, calculated from SEM studies. The film has exhibited compact and dense structure. The work reported in this paper will be useful in tailoring the optical properties of Ta2O5 as per requirement.

Using first-principles calculation for the electronic structures of nm-scale [0001] GaN freestanding films, it is found that the Ga-terminated surface (SGa) has a positive electrostatic potential, while the N-terminated surface has a negative electrostatic potential (SN), so that the energy bands tilt upwards from SGa to SN. Additionally, it is determined that an intrinsic self-regulated charge transfer across the film limits the electrostatic potential difference across the film, which renders the local conduction band energy minimum at SGa approximately equal to the local valence band energy maximum at SN. This effect is found to occur in films thicker than ~4 nm. If the dangling-bond/surface states at both SGa and SN are passivated by pseudo-hydrogen atoms, the tilt of energy bands is similar, though the cross-film potential is reduced due to the extra H5/4-Ga and N-H3/4 dipole layers.

This paper presents a new method to simulate the properties of Frequency Selective Surface (FSS) composed of planar H-shaped fractals structure exhibiting multiple band gaps of electromagnetic waves. The FSS sample can be easily fabricated as that of the Printed Circuit Board (PCB). The electromagnetic characteristics of this H-shaped fractal structure were studied mainly by numerical simulation based on Finite Integration Technique (FIT). The simulation results present a direct image of surface currents when certain frequency electromagnetic waves incident on the surface of the sample, which is in a considerably good agreement with the experimental results. Based on the comparison of simulated and experimental result it is suggested that the planar H-shaped fractals structure has quasi-periodic multiple band gaps and the size can be significantly smaller than the relevant electromagnetic band gap wavelength.

We characterize a method of heat-assisted magnetic recording (HAMR), which may be applied for high-density probe storage system. The magnetic recording medium is a CoNi/Pt multilayered film, suitable for perpendicular recording. The heating source is the field emission current from a scanning tunneling microscopy (STM) tip, with pulse voltages added between the tip and the film. Writing shows a threshold voltage of 4 V. Marks with an average size of 165 nm were achieved for pulses above 4 V. A model of dynamic domain formation is applied to simulate the process of the formation of marks. The effect of domain wall forces is discussed. Simulation results agree with experiments well, without the need of taking domain wall forces into account.

Polycrystalline electroceramics have been prepared by varying modifier to former (Bi/La) ratios ($z/1-z$) according to the complex formula Pb0.92[La$_{1-z}$Biz] 0.08[Zr0.65Ti0.35] 0.98O3 (PLBZT), where z = 0.0, 0.3, 0.6. The electrical properties of PLBZT compounds were studied using the ac impedance spectroscopy technique over a wide range of temperature (30–500 °C) in the frequency range of 100 Hz–1 MHz. Nyquist plots recorded at different temperatures show a decrease in the bulk resistance (Rb) with rise in temperature for PLZT material (z = 0.0) i.e., NTCR behavior like semiconductors. The Nyquist plots also indicates that the bulk resistance of the material has been observed to be concentration dependent and decreased in two order of magnitude with higher Bi-addition in PLZT matrix. Bismuth (Bi) substitution at the lanthanum (La) position not only resulted in lowering of the electrical resistance with its higher concentration but also has changed the NTCR behavior of PLZT (z = 0.0) to PTCR (positive temperature coefficient of resistance) for PLBZT. Electrical property studied by complex impedance spectroscopic method also indicates the evidence of (i) single electrical relaxation attributed to the presence of bulk contribution to the electrical properties, (ii) presence of temperature dependent electrical relaxation phenomenon and (i) diminution in the barrier to the mobility of charge carrier on Bi-substitution.

Recent experimental studies of electrical conduction in a specially prepared silver-based material, across which a spark has been passed, are interpreted through electrical conduction via charge density waves (CDWs) moving in a dc electric field along quasi-one-dimensional chains of Ag+-ions inside the branches of the discharge pattern engraved in the material by the spark. Here we present experimental evidence that the resistance along a number N of branches connected in parallel increases in quantized steps of height $h/2e^{2}N$ with increasing voltage applied across the branches

This paper concerns non linear dielectric spectroscopy in the SmC* phase of a ferroelectric liquid crystal. The experimental set-up and the procedure used to determine non linear permittivities are described. The results are discussed on the basis of the model proposed by Kimura et al. [Y. Kimura, S. Hara, R. Hayakawa, Phys. Rev. E 62, R5907 (2000); Y. Kimura, S. Hara, R. Hayakawa, Ferroelectrics 245, 61 (2000)]. A good agreement is obtained between the measurements and the theoretical predictions for $\epsilon^{*}_{3,3}$ and $\epsilon^{*}_{5,5}$ non linear permittivities. Some physical parameters of the material like the polarization, the rotational viscosity and the elastic term are determined. The polarization is found similar to this obtained with classical triangular wave method.

This paper discusses some aspects of n-hexane soot reactivity in a multi-pin to plate pulsed corona discharge working in the nanosecond regime at atmospheric pressure. The soot-discharge interaction was quantified by measuring the densities of CO, CO2, O3 and NO2 out-coming from the discharge cell. Results showed that CO2 is the major product of soot oxidation. They also showed a strong enhancement of soot oxidation for O2 percentage greater than 10% and cathode temperatures above 425 K. The soot reactivity is significantly enhanced when the discharge frequency is increased. The results obtained were interpreted in term of the competition between the kinetics of plasma active species adsorption and oxidation product desorption.

We propose a new technique for evaluating the RF voltage across the electrodes of low-pressure capacitively-coupled plasma reactors when direct measurements are not possible. It is based on determining the coordinates of the turning point in the RF breakdown curve and using known values of the electron drift velocity for the gas. The results are in good agreement with those obtained by direct measurements at the driven electrode. Furthermore it allows RF breakdown curves to be determined for different frequencies, giving results that are physically reasonable (coincidence of right-hand branches) and in agreement with other published results. The technique for determining RF voltage we proposed is valid when there is no discharge plasma between electrodes (e.g., before gas breakdown), as well as for negligibly small discharge currents (before extinction of the weak-current discharge mode).

This article deals with the analysis of small sample volume by using a planar microcoil and a micromachined cavity. This microcoil is used as a nuclear magnetic resonance (NMR) radio frequency detection coil in order to perform in vitro NMR analysis of the sample introduced into the microcavity. It is a real challenging task to develop microsystem for NMR spectrum extraction for smaller and smaller sample volume. Moreover, it is advantageous that these microsystems could be integrated in a Micro Total Analysing System ($\mu $-TAS) as an analysing tool. In this paper, NMR theory, description, fabrication process and electrical characterization of planar microcoils receiver are described. Results obtained on NMR microspectroscopy experiments have been performed on water and ethanol, using a 1 mm diameter planar coil. This microcoil is tuned and matched at 85.13 MHz which is the Larmor frequency of proton in a 2 T magnetic field.

We report measurements of the birefringence-induced losses in silicon single crystals for [001] and [111] crystallographic orientation and for different doping levels. These results are compatible with the so-called spatial-dispersion-induced birefringence in cubic crystals. These angular maps have been used to fix some tolerances for the next generation of optics in the Virgo gravitational-wave detector.

This paper aims to evaluate the spatial resolution achievable with immersion objective lenses for electron emission microscopy. The simulations, using Simion 7 software, follow a brief reminder of objective lens properties as determined by analytical studies. In general, the aperture and chromatic aberrations should be characterised concurrently since the aperture stop causes an energy-dependent angular discrimination. This last effect adds to the longitudinal chromatic shift produced during the initial electron acceleration. The simulation is applied first to monochromatic electron beams for PEEM objective lenses described in the literature and for several other lens configurations. Then, for energy dispersed electron beams (0.2–2, 0.2–4,..., 0.2–10 eV), the image quality is deduced from density plots involving convolution weighting factors which include the change in angular acceptances. It is shown that PEEM objective lenses associated with an aperture stop of a diameter of 30 µm, may provide resolutions below 2 nm for electrons emitted within the initial energy window 0–10 eV. However for the same aperture stop and a moderate acceleration voltage of 4000 V other objective lenses might provide equally good resolutions. The acceleration bias mode for the focussing element seems especially promising since all along their paths the electron beams keep high energy and are thus less submitted to residual magnetic fields. Also the misalignment effects caused by the electrostatic field disturbances on the sample surface are reduced when a quite long acceleration length is used: the object nodal point being removed far from the emitting surface.

The harmful effect of toxic chemicals on natural ecosystems has led to an increasing demand for early-warning systems to detect those toxicants at very low concentrations levels. Whole-cell biosensors based either on chlorophyll fluorescence or enzyme (phosphatase and esterase) inhibition are constructed for real-time detection and on-line monitoring. Results show that these devices are sensitive to heavy metals and pesticides. The system allows the cells to operate in their natural environment which favours long term stability and reflects the toxic action mechanism providing therefore an ecological interest.