This experimental work presents reproducible measurement conditions to allow amplification of the mechanical vibration generated by photo-thermo-acoustics (PTA) effect using the resonance of circular silicon membranes clamped by nitrile o-rings on a diameter of 30 mm (Di ). We use wafers with various thickness (h) between 250 and 1000 μm and with carrier lifetime between 3 and 30 μs. Under the condition to have a resolution of few picometers for the measurement, it is possible to characterize the resonance mechanism obtained without contact by conventional laser vibrometry using a modulated laser diode of only a few milliwatts of power. Compared to perfect clamped membranes, the first Eigen frequency presents a downward shift of some hundreds Hertz due to the circular clamping by o-ring as predicted by our simplified model. The resonance frequency depends linearly on the thickness as long as Di /h > 80. The quality factor (Q) does not exceed ten in agreement with our model for spring loaded membrane in air. The low value of quality factor and its variation according to thickness follow our predictions. Moreover, Q is independent of carrier lifetime whereas first resonance amplitude increases with it but less than prediction for bulks.

A simple and effective method is presented to fabricate surface-roughened InGaN/GaN-based light emitting diodes (LEDs) epistructure using annealing-formed, random-distributed Au particle arrays as dry etching mask. The shapes of GaN nanoislands, with horizontal diameters of 100–500 nm and vertical depths up to 140 nm, are determined by Au mask particles. Importantly, this roughened surface exhibits strong photoluminescence (PL) light-output enhancement by a factor of more than 1.6 orders of magnitude. This method will put forward new promising applications in the electroluminescent devices, especially in solid state lighting.

Spin-polarized low-energy electron microscopy (SPLEEM) is a technique for imaging magnetic microstructures at surfaces and in thin films. In this article, principles, advantages and limitations of SPLEEM are reviewed. Several recent studies illustrate how SPLEEM can be used to investigate spin reorientation transition phenomena, to determine magnetic domain configurations in low-dimensional structures, or to explore physics of magnetic couplings in layered systems. The work highlights the capability of the technique to reveal in situ and in real time quantitative information on micromagnetic configurations and structure-property relationships. In addition, spectroscopic reflectivity measurements with spin-polarized low-energy electron beams can be a useful tool to probe spin-dependent unoccupied band structure of magnetic materials and electronic properties of buried magnetic interfaces.

In this paper, the authors present a new theory that can be applied to predetermine the value of cutoff temperature of operation (Tcutoff ) of uncooled semiconductor laser diodes. Tcutoff is defined as the value of temperature of operation above which, the turn-on time delay ton of uncooled SLD will exceed the bit time interval of the injected pulse and results in an inoperable case. An analytical model is derived to represent the temperature dependence of ton . This model is used to derive an accurate one for Tcutoff and in terms of laser cavity parameters. Simulation results show that Tcutoff can be increased (improved) by increasing the injection current or biasing the uncooled SLD near threshold. The benefit of this study is that the designer could predetermine previously the requirements that should be taken into account, when considering of uncooled SLD in high-speed optical communication systems.

In this paper, some of the results of dielectric study carried out using locally produced low cost Fe2O3 powder with 0.5 wt% of Si additive are being summarized. The dielectric properties were studied as a function of composition, frequency and temperature for a series of Mnx Zn1-x Fe2O4 ferrite. The samples were prepared by the usual ceramic technique. It was observed that the values obtained for dielectric constant ∈′ and dielectric loss factor tan δ are much lower than those normally obtained for Mn-Zn ferrite prepared by pure Fe2O3 powder. The low values are attributed to the presence of Si, which suppress the ceramic grain growth. The low dielectric loss makes these samples attractive for use at high frequencies. Each of ∈′ and tan δ increases on increasing the temperature. Abnormal dielectric behavior observed for x = 0.99 due to forced migration of Fe ions from A sites to B sites at this composition.

We investigated the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of identically prepared safranine T/p-Si organic/inorganic Schottky devices (total 26 diodes) formed by evaporation of organic compound solution on p-Si semiconductor substrate. It was seen that the safranine T organic thin film on the p-Si substrate showed a good rectifying behavior. The barrier heights and ideality factors of all devices were extracted from the electrical characteristics. The mean barrier height and mean ideality factor from I-V measurements were calculated as 0.59±0.02 eV and 1.80±0.20, respectively. Also, the mean barrier height and mean acceptor doping concentration from C-V measurements were calculated as 0.67±0.10 eV and (6.96±0.37)×1014 cm-3, respectively. The discrepancy in the barrier height values obtained from I-V and C-V characteristics has been attributed to different nature of the measurements. The discrepancy between these values can also be due to the existence of the interfacial native oxide and the organic safranine T thin layer between the semiconductor substrate and top contact metal.

In this study, Ag/OD-MO/Ag surface-type diode was fabricated by drop-casting orange dye and methyl orange blend thin film from 1.0 wt.% aqueous solution, under the effect of an electric field, on a glass substrate with preliminary deposited silver electrodes. Geometrical length and width of the semiconducting channel between metallic electrodes were equal to 40 μm and 21 mm, respectively. The dark I-V characteristics exhibited strong rectification behaviour though both electrodes were from the same metal. The average value of rectification ratio (RR) was 27 and it was found that RR varies with applied voltage in the range of 1–40. The dark I-V characteristics were simulated by modified Shockley equation and space-charge limited currents (SCLC) approach. Different diode parameters were calculated from current-voltage characteristics. The diode showed non-ideal I-V behaviour with a quality factor greater than unity. Energy band diagram is proposed for the Ag/OD-MO/Ag surface-type diode.

In order to measure the dielectric permittivity of thin insulting layers, we developed a method based on electrostatic force microscopy (EFM) experiments coupled with numerical simulations. This method allows to characterize the dielectric properties of materials without any restrictions of film thickness, tip radius and tip-sample distance. The EFM experiments consist in the detection of the electric force gradient by means of a double pass method. The numerical simulations, based on the equivalent charge method (ECM), model the electric force gradient between an EFM tip and a sample, and thus, determine from the EFM experiments the relative dielectric permittivity by an inverse approach. This method was validated on a thin SiO2 sample and was used to characterize the dielectric permittivity of ultrathin poly(vinyl acetate) and polystyrene films at two temperatures.

In this work, we present noise analysis in a Single Electron Photo-detector (photo-SET or nanopixel) able to detect one by one electron. We perform the power spectral densities (PSD) of random telegraph signals (RTSs) measured in the dark conditions and under light illumination. Photoinduced RTS can be attributed to the charging of a dot near the current path. From these results, photogenerated traps were identified. It is also found that RTS fluctuations depend on the light wavelength.

Yttrium iron garnet (YIG) film made as a magneto-optical medium suffers from the problem of crack formation, caused by the heating process. YIG thin film is deposited by radio frequency rf magnetron sputtering; the obtained layer is amorphous and it needs annealing to be crystallized. After heat-treatment at 740 ○C of the sample realized on quartz substrate, we observe cracks on the entire film surface. This is due to the large difference between the thermal expansion coefficient (5.5 ×10-7 K-1 for quartz and 10 ×10-6 K-1 for YIG). In this paper we present a new fabrication method to reduce this problem, we make a multilayer to obtain at the end a uniformly unique layer with excellent crystalline structure. Such films have the possibility to reach a thickness of 500 nm. YIG films have been studied by Rutherford backscattering spectrometry (RBS), optic ellipsometry and the scan electron microscope. The RBS spectra were collected in channelling geometry with incident particles energy 2 MeV and 3.5 MeV. The thickness and the stoichiometric value of the thin films have been evaluated. Simulation of all spectra indicates a constant composition. Ellipsometry method is well adapted to model the thin film structure layers, and to measure the thickness of the film and the complex index of refraction. The theoretical ellipsometric value of the index of refraction is (2.22) while the experimental value is ranging from 2.2 to 2.3 for a wavelength of 1550 nm.

The strain-dependent electronic structure of graphene ribbons is studied based on tight-binding theory. The change of ribbons in applied electric field brought by strain is revealed. In contrast to normal strain, it is found that shear strain yields new transverse electric field which is similar to Hall effect. The conductance of ribbons under uniform uniaxial strain is calculated in Landauer formula. It is obtained that the conductance decreases (increases) 1.62% (1.64%) under the 0.5% uniaxial tension (0.5% compression) for a 200 nm-width ribbon.

Analytical models for the piezoelectric excitation and for the wet micromachining of resonant cantilevers are proposed. Firstly, computations of metrological performances of micro-resonators allow us to select special cuts and special alignment of the cantilevers. Secondly the self-elaborated simulator TENSOSIM based on the kinematic and tensorial model furnishes etching shapes of cantilevers. As the result the number of selected cuts is reduced. Finally the simulator COMSOL® is used to evaluate the influence of final etching shape on metrological performances and especially on the resonance frequency. Changes in frequency are evaluated and deviating behaviours of structures with less favourable built-ins are tested showing that the X cut is the best cut for LGS resonant cantilevers vibrating in flexural modes (type 1 and type 2) or in torsion mode.

The performances of organic photovoltaic cells based on the layer couple electron donor/electron acceptor (ED/EA) are significantly improved when an exciton blocking layer (EBL) is inserted between the organic acceptor and the cathode. A new material, the (Z)-5-(4-chlorobenzylidene)-3-(2-ethoxyphenyl)-2-thioxothiazolidin-4-one, that we called (CBBTZ), has been synthesized, characterized and probed as EBL. The energy levels corresponding to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the CBBTZ have been determined from the first oxidation and reduction potential respectively, using cyclic voltametric (CV) measurements. From CV curves, CBBTZ in dichloromethane showed a one electron reversible reduction and oxidation waves. The values of its HOMO and LUMO have been estimated to be 6.42 eV and 3.42 eV respectively. Such values show that CBBTZ could be probed as EBL in organic solar cells based on the ED/EA couple copper phthalocyanine(CuPc)/fullerene (C60). The photovoltaic solar cells have been obtained by sequential deposition under vacuum of the different films. The different thin film thicknesses were measured in situ by a quartz monitor. Multilayer solar cells ITO/Au/CuPc/C60/EBL/Al have been probed, where EBL is the aluminium tris(8-hydroxyquinoline) (Alq3), the CBBTZ, the 2-(4-byphenylyl)-5-(4-tert-buthylphenyl)-1,3,4-oxadiazole (butyl PBD) or the bathocuproine (BCP). The optimum film thickness is 8–9 nm whatever the EBL used. When obtained in the same run, the averaged efficiency of the cells using the CBBTZ is of the same order of magnitude than that obtained with BCP and higher than that achieved with Alq3 or butyl PBD. It is shown by XPS study that some aluminium of the cathode is present in the buffer layer. This aluminium could justify the ability of the electrons to cross the insulating exciton blocking layer thick of 9 nm.

Herein the synthesis and the crystal growth of benzoyl valine (BV), an organic nonlinear optical (NLO) material for frequency conversion was grown by slow evaporation solution growth technique at room temperature has been reported. The compound was prepared by Stockman method of benzoylation. The solubility curve shows linear nature up to a temperature of 313 K. XRD study reveals that the crystal belongs to monoclinic system with P21 non-centrosymmetric space group. The fundamental vibrational frequency of various functional groups (400-4000 cm-1) in the crystal was determined from FTIR analysis. 1H and 13C NMR spectral studies reveal the presence of proton and carbon network in the grown crystalline sample. The optical behaviour of the crystal was ascertained by optical UV absorption spectral studies. The UV cut off region (λmax ) lies around 200 nm and the crystal is absolutely transparent from 220–800 nm suggesting its application as NLO material. The thermal stability of the crystal was determined by thermogravimetric and differential thermal analyses. Laser damage threshold of BV was found to be 0.34 GW/cm2 and hence BV can be used in frequency doubler system. Photoconductivity study of BV revealed negative photoconductiviting nature of the sample. The microhardness studies confirm that BV has a moderate Vickers hardness number (VHN) value in comparison to the other organic NLO crystals.

Within the Landauer framework of ballistic transport, we theoretically investigate spin-dependent resonant transmission and magnetoresistance in symmetric cascade junctions of ferromagnetic metal (FM) and semiconductor (SC). It is shown that spin-up and spin-down electrons possess different bandgap structures against the Rashba spin-orbit wave vector. Due to the mirror symmetry, multiple spin-dependent perfect transmissions of electrons can be obtained within the bandgap, thereafter, spin polarization has multiple reversals. Around each resonant wave vector, high spin polarization is achieved and the electrical conductance comes from one kind of spin electrons. The resonant transmissions originate from the spin-dependent quasi-bound states at energies above the potential barriers, which are demonstrated by the electronic charge distributions in the system. Furthermore, if we change the magnetization of FM in the centre of the junctions, inverse magnetoresistance can be observed. The investigations may have potential applications in spin filters and spin switches.

GaN nanowires doped with Dy have been fabricated on Si (111) substrate through ammoniating Ga2O3 films doped with rare earth phosphor. The samples are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM) and photoluminescence (PL). The results demonstrate that the Dy-doped GaN nanowires were single crystalline with hexagonal wurtzite structure. The diameters of the nanowires were about 50 nm and the lengths were up to several tens micrometers. Also, the optical properties of the nanowires were greatly dependent on the doping of Dy. The growth mechanism of crystalline GaN nanowires is discussed briefly.

The improvement of corrosion resistance of ZrN1-x Cx films (0 ≤ x ≤ 1) on AISI stainless steel (ss) 304 is studied as a function of methane flow rate introduced into mixture of argon and nitrogen gases (Ar + N2). The films were deposited using ion beam sputtering technique at 400 °C and their corrosion resistance has been investigated via electrochemical test using 0.5 M H2SO4 solution. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to study the micro and nano-structures of the films. Film stoichiometry was determined by Rutherford backscattering (RBS) technique using SIMNRA code. An average grain size of 7 nm was calculated for deposited films using Scherrer's formula. X-ray diffraction results showed the presence of a transition crystalline phase from ZrN to ZrC phase corresponding to the formation of ZrN1-x Cx crystalline phase. The electrochemical test revealed that the film corrosion resistance increased with increasing x values. Furthermore, micrographs obtained by SEM did not indicate any damage on the sample surface due to corrosive agent attacks for x > 0.6.

The spectroscopic emission of zinc plasma along with CCD imaging profile has been studied. The zinc target has been irradiated with a Q-switched Nd:YAG laser (1064 nm, 290 mJ, 10 ns, 29 MW) in air at atmospheric pressure. The plasma emission is recorded with 100 ns integration time. Boltzmann plot method and Stark broadening profile of the transition line has been used to estimate the electron temperature (Te ) and electron density (Ne ) respectively. Estimated values of Te and Ne is in the range of (5700–6756) K and (1.6 × 1015-3.39 × 1015) cm-3 at three laser shots respectively.

We study the radiative heat transfer between a spheroidal metallic nanoparticle and a planar metallic sample for near- and far-field distances. In particular, we investigate the shape dependence of the heat transfer in the near-field regime. In comparison with spherical particles, the heat transfer typically varies by factors between 1/2 and 2 when the particle is deformed such that its volume is kept constant. These estimates help to quantify the deviation of the actual heat transfer recorded by a near-field scanning thermal microscope from the value provided by a dipole model which assumes a perfectly spherical sensor.

Based on the vector angular spectrum theory of electromagnetic waves and the method of stationary phase, analytical vector structures of four-petal Gaussian beams (FPGB) in the far field are derived. The energy flux for the TE term, TM term and the whole beam are represented and illustrated with numerical examples. Effects of beam orders and paraxial degrees on energy flux distributions are discussed in detail, and the corresponding analytical explanations are also given. These results may provide a new approach to manipulate other higher-order laser beams in the far field.