The bulk micromachining on (010), (110) and (111)A GaAs substrates in the 1 H2SO4:1 H2O2:8 H2O system is investigated. Focus is placed on anisotropy of 3D etching shapes with a special emphasis on convex and concave undercuts which are of prime importance in the wet micromachining of mechanical structures. Etched structures exhibit curved contours and more and less rounded sidewalls showing that the anisotropy is of type 2. This anisotropy can be conveniently described by a kinematic and tensorial model. Hence, a database composed of dissolution constants is further determined from experiments. A self-elaborated simulator which works with the proposed database is used to derive theoretical 3D shapes. Simulated shapes agree well with observed shapes of microstructures. The successful simulations open up two important applications for MEMS: CAD of mask patterns and meshing of simulated shapes for FEM simulation tools.

This paper presents the result of thermodynamic studies on (Se80Te20)100-xAgx ( 1< x < 4)glasses under non isothermal conditions using differential scanning calorimetric technique. Thecrystallization kinetics has also been discussed. Thermodynamic parameters like entropy difference betweenglassy and the crystalline phase, difference of Gibbs free energy, specific heat, and the enthalpy released during phase transformation have been evaluated. The heat capacity jump and fragility of these alloys are alsocalculated. The results show that the stability of sample is minimum for (Se80Te20)99Ag1 and maximum for (Se80Te20)97Ag3 among all the samples.

We address the interpretation of the splitting between the ground state excitonic transition which indicates the energy of the lowest direct band gap in AlN bulk films and epilayers, and a 36–38 meV higher energy companion. We demonstrate that this splitting is consistent with the initial interpretation in terms of 1s–2s excitonic splitting by using a calculation of the exciton binding energy which includes mass anisotropy and anisotropy of the dielectric constant. Analytical expressions are proposed to compute the evolution of 1s and 2s excitonic energies using an anisotropy parameter. We show that the values of the dielectric constant that are required to fit the data are $\varepsilon _{\bot}$ ≈ 8.7and $\varepsilon _{\parallel}$ ≈ 10, values different from the couple of values $\varepsilon _{\bot}$ ≈ 7.33 and $\varepsilon _{\parallel}$ ≈ 8.45 erroneously obtained after a fitting procedure using a spherical description of the long range Coulomb interaction and the classical textbook n-2 spectrum of the excitonic eigenstates. Starting from now, our values are the recommended ones.

Co-doped GeO2 ceramic films were prepared via a liquid phase co-deposition (LPCD) process. The oxide samples were transformed into Ge1-xCox films (x = 0.75, 3.2 and 11.5%) after annealing under hydrogen atmosphere. The crystallinity of Ge1-xCox film decreases with increasing Co content. The Ge1-xCox films are p-type (hole density 1020 ~ 1021 cm-3). The 3.2% film has higher electrical conductivity and hole density compared with the other two samples. The 0.75% film is superparamagnetic at 300 K while the 3.2% and 11.5% films exhibit blocked superparamagnetic behaviors. Hysteresis loops can be observed in the magnetization curves of the 3.2 and 11.5% samples. The observed ferromagnetisms are on only a local (a few nanometers) scale, which most likely arise from different size and chemical distribution in every sample.

A systematic method for the design of potential microstructure configurations of structural left-handed materials (LHMs) based on topology optimisation technique is presented, and a single objective and a multi-objective optimisation model are proposed. The material considered is a periodic array of dielectric substrates attached with metal film pieces, and the microstructure design of left-handed material is formulated through determining the arrangements of those metal pieces. Different from the conventional configurations of LHMs which consist of magnetic resonators and wires, our results showed that novel integrative configurations without wires can be obtained as microstructures of LHMs. Topology optimisation technique is a universal and effective tool for configuration design of LHMs, and many new structural LHMs with the desired electromagnetic characteristics can be obtained by this systematic approach.

Fluorine doped ZnO thin films (FZO) are prepared onto glass substrates at 350 °C by the chemical spray pyrolysis technique. X-ray diffraction spectra show a polycrystalline of ZnO (wurtzite structure) where the amount of fluorine doping affects to preferential orientation (002 plane along c-axis) and does not vary the lattice parameters. Therefore, F introduction in lattice is by the substitution of O-2 ions by F-1 ions. Any variation is observed in transmittance and reflectance measurements in 400–2000 nm wavelength range when samples present F dopant; they have transmittance around 80% in the near infrared and visible zones. The FZO films are degenerate and exhibit n-type electrical conductivity. The best resistivity and mobility are 7.6 × 10-3 Ω cm and 3.77 cm2 V-1 s-1 respectively. The calculated values of the mean free path are very small compared to the grain sizes calculated using XRD measurements. Therefore, we suggest that ionized impurity and/or neutral impurity scattering are the dominant scattering mechanisms in these films.

In this study, TiO2 films were grown at room temperature by sol-gel process using titanium (IV)-isopropylatas precursor. XRD, EDS and MEB analyses proved that an eventual annealing treatment caused the TiO2 amorphous phase to shift to a crystalline anatase phase. Optical measurements were carried out via absorbancespectra in 500–2500 nm wavelength domain. From these optical measurements, the temperature-dependent conjointoptical and thermal properties were deduced using the Amlouk-Boubaker opto-thermal expansivity ψAB.

In this investigation, transparent TiO2 nanotube arrays prepared on a FTO substrate are employed as 1D nanostructuresproviding elongated direct pathways for electron transport and collection in solid-state dye-sensitized solar cell (SDSC). Donor-antenna (D-A) dyes provide an exciting route for improving the light harvesting efficiency in dye sensitized solar cells owing to their high molar extinction coefficients and the effective spatial separation of charges in the charge-separated state. Hence in this study we fabricated SDSC devices with different thicknesses of transparent TiO2 nanotube array electrodes sensitized with Ru-(II)-donor-antenna dye and spiro-OMeTAD as a hole conductor. At AM 1.5 G, 100 mW/cm2 illumination intensity, a power conversion efficiency of 1.94% was achieved when the TiO2 nanotubes are initially subjected to TiCl4 treatment. Furthermore, a linear increase in the cell current without loss in fill factor is observed for increasing length of TiO2 nanotubes. The structural and morphological characteristics of the transparent TiO2 nanotube arrays as well as the optimal conditions for the fabrication of SDSCs with transparentTiO2 nanotubes on FTO glass are reported.

The atomic edges of graphene nanoribbons with anomalous geometry structure were very recently observed in experimental evidence by [Koskinen et al., Phys. Rev. B 80, 073401 (2009)]. We present first-principles calculation to investigate the electronic structures and transport properties of graphene nanoribbon with anomalous edges (two configurations, namely 5-7-7 edge and 5-6 edge). Electronic band results demonstrate that the Fermi level is downward shifted due to the formation of the anomalous edges in these configurations. The band gap is substantially increased as a result of the presence of the 5-7-7 edge. Furthermore, the conductance below the Fermi level presents more prominent variation in the 5-6 edge configuration, indicating that this defect mainly affecting its valence bands. Our results provide the possibility of new approaches to control the electronic transport properties of graphene nanoribbons via tailoring the atomic structure of their edges.

The diffraction of Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis is studied. Analytical expressions for the components of the diffraction field are derived and illustrated by numerical examples. Results indicate that, upon diffraction of Gaussian vortex beams inside uniaxial crystals, components of the transversal and longitudinal electric fields would vary and show different characteristics. Effects of anisotropic crystals on intensity distributions of Gaussian vortex beams are also investigated. It demonstrates that, upon diffraction, intensity distributions would be distorted and rotated into elliptical profiles with the variation of the ratio of refractive indices. These influences may finally cause the non-symmetry of the intensity distributions of laser beams.

A technique based on a tree-cotree decomposition, called Spanning Tree Technique (STT) in this paper, has been shown to be simple and efficient to compute the generalized source magnetic fields for h-oriented magnetostatic formulations when solenoidal source electric currents over the faces of the mesh are given as input. Yet, it has been recently shown that STT may frequently fail in practice.Other techniques, which circumvent STT problems, have been proposed in literature. However, all of them greatly worsen the computational complexity and memory requirements regarding the source field computation.The aim of this paper is to present a generalization of STT called Extended Spanning Tree Technique (ESTT), which is provably general and it retains the STT computational efficiency.

We studied the structural and dielectric properties of new Tetragonal Tungsten Bronze (TTB) ceramics Pb1.85K1.15Li0.15Nb5O15 that was synthesized by solid-state reaction. We pay a special attention to the diffuse phase transition (DPT) that occurs close to 425 °C. Using dielectric measurements in a frequency range of 10 Hz–1 MHz and in the temperature range 30–560 °C, we have shown that the real permittivity close to DPT is well described by Santos-Eiras phenomenological model. Space-charge polarization, relaxation phenomena and free charges conductivity have been analyzed using dielectric spectroscopy impedance and modulus characterization. Cole-Cole plots show a non-Debye (polydispersive) type relaxation. In paraelectric phase the Arrhenius activation energy was determined as Eτ = 0.72 eV. We demonstrated that frequency dependence of ac conductivity at different temperatures obeys the Jonscher's universal law: σac = σdc + A(ω)n.

The local structures and the spin Hamiltonian parameters for the substitutional Nb4+ centers in MO2 (M = Sn, Ti and Ge) crystals are theoretically studied using the perturbation formulas of these parameters for a 4d1 ion in a rhombically compressed octahedron. The above Nb4+ centers are found to experience the Jahn-Teller distortions, characteristic of the relative axial compressions (~ 0.01–0.02 Å) and the non-axial (planar) angular increases (~ 3°). As a result, the ligand octahedra are transformed from original elongation on host tetravalent cation sites to compression in the impurity centers, with additional non-axial distortions smaller than those in the hosts. The influences of the Jahn-Teller distortions and the ligand orbital contributions are also analyzed.

The electrical characteristics of DBD have been studied using four different barriers. These barriers are Pyrex glass, Mylar, porous alumina Al2O3 plates and ceramic plates of composition (50% MgO:50% Al2O3). It has been found that the type and the internal composition of the dielectric barriers affect the formation of the DBD modes. Using glass or Mylar as a dielectric causes the formation of the filamentary DBD mode. While using porous alumina plates leads to the generation of the discharge in APGD mode. A quasiglow mode is obtained when a ceramic of composition (50% MgO:50% Al2O3) is used. The effect of using one dielectric barrier, on the DBD characteristics has also been studied. Antisymmetric behavior of the current waveform is obtained when one dielectric barrier is placed on the life electrode.

This work deals with the characterization of the conductivity tensor of a carbon fiber reinforced polymer composite (CFRP) thin plate. We propose a contactless method based on the eddy current non destructive testing technique. The used eddy current sensor consists of a ferrite torus on which a winding is wound. The torus is of a rectangular section and contains a thin air-gap in which the thin CFRP plate is inserted. We developed analytical relations giving the longitudinal and transversal conductivities of the CFRP plate as functions of the impedances variations of the eddy current sensor, corresponding to the orientations of the carbon fibers parallel and transverse to the direction of the torus width which is much greater than its thickness. The analytical relations are developed by inverting interpolation functions of curves giving the variations of the sensor impedances as functions of the longitudinal and transversal conductivities of the CFRP plate. These curves are obtained by a numerical model based on a simplified integro-differential formulation in terms of the electric vector potential in the CFRP plate, coupled to the magnetic circuit equations in the ferrite torus. The modeling results are supported by measurements.

Auger electron spectroscopy and the surfacemagneto-optical Faraday effect were used to monitor the depositionof Co ultrathin films on an initially rough ZnO(002) crystalsurface. The magnetic properties of the epitaxial films werecompared with those associated with that the structure properties ina 3D island growth mode. The magneto-optic signals are verysensitive to the thickness of the Co film structure, even if it isrough. The ZnO(002) substrate surface formed by routine ionsputtering may exhibit short-range ordering in the initial samplepreparation. The roughness of a sputtered substrate surface can bedetermined from the sensitive magneto-optical signals, especiallywhen ultrathin films are deposited in the initial stage of growth.