In this work we report on the characteristics of (Ni/Au)/AlGaN/GaN/SiC Schottky barrier diode (SBD). A variety of electrical techniques such as capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) measurements were used to characterize the diodes. We observed an hysteresis phenomenon on the C-V characteristics in the Schottky diode. The parasitic effect can be attributed to the presence of traps in the heterostructure. Deep defects analysis was performed by deep-level transient spectroscopy (DLTS). One hole trap have been detected with an activation energy and a capture cross-section of 0.75 eV and 1.093 × 10−11 cm2. The localization and the identification of this trap have occurred and a correlation between the defect and the hysteresis phenomenon has been discussed. At high temperatures, the DLTS signal sometimes becomes negative, likely due to an artificial surface-state effect.

In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27–300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 106 and 6.60 × 106 cm/s at an electric field of around E ~ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large non- equilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.

Chemically sprayed aluminum-doped ZnO (1% Al) and undoped ZnO thin films were deposited on glass substrates at T = 420 °C. The thin films are characterized by X-ray diffraction and scanning electron microscopy. The characterization results show that all the compounds are wurtzite with hexagonal structure (0 0 2). They are well crystallized and the grain size is (e = 0.1 μm) for undoped ZnO and (e = 0.13 μm) for Al-doped ZnO. The prepared Al-doped ZnO showed good gas responses to ethanol for two concentrations 200 ppm and 400 ppm. Short response time is given by Al-doped ZnO comparing with undoped ZnO films, its estimate at (~10 s) and recovery time (~15 s) to 200 ppm at T = 220 °C.

The temperature dependence of the I-V characteristics on Au/Ni-HEMT Schottky contacts was measured and analyzed. Large deviations from the thermionic emission and thermionic-field emission model were observed in the I-V-T characteristics. The thin surface barrier model only fits the measured curves in the high bias region, but deviates drastically in the low bias region. Using a revised thin surface barrier model, the calculated curves match well with the measured curves. It is also found that tunneling emission model is the dominant current transport mechanism at low temperature, yet thermionic-field emission model is the dominant current transport mechanism at high temperature.

Pentacene field-effect transistors (FETs), fabricated on strontium titanate without self-assembled monolayer, showed mobility as high as 1.9 cm2/V s at operating voltage as low as −3 V. The mobility of the FET was significantly increased to attain 3.3 cm2/V s simply by storage in a desiccator for 1032 h. Based on careful examination of the time dependence of the mobility for the FET devices, it was indicated that the mobility significantly increased in initial stage to several thousand hours and then monotonously decreased beyond then regardless of the initial value of the mobility.

By engineering the interface between the intermediate photoactive layer and the cathode aluminum (Al) electrode, through the introduction of ultra-thin layers of various materials, in a standard bulk heterojunction (BHJ) polymer solar cell (PSC) fabricated of regioregular poly(3-hexylthiophene) (rr-P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), the power conversion efficiency (PCE) has been effectively improved. The devices fabricated using individual single interlayer of bathocuproine (BCP), lithium fluoride (LiF) and Buckminster fullerene C60 have shown optimal efficiencies of ~2.40%, ~3.21% and ~1.92% respectively. Further improvement of the photovoltaic efficiency was achieved by introducing a composite bilayer made of LiF in combination with BCP as well as with C60 at the BHJ/cathode interface. The best results were obtained by interposing a 9 nm of C60 interlayer in combination with a 0.9 nm thick LiF layer, with the PCE of the PV cells being effectively increased up to 3.94% which represents an improvement of 23% as compared to the standard device with LiF interlayer alone. The photocurrent density (Jsc) versus voltage (V) characteristic curves shows that the increase of the efficiency is essentially due to an increase in Jsc. Moreover, all the sets of devices fabricated using various interlayers over a certain range of thickness exhibit an optimum PCE that is inversely proportional to the series resistance of the PV cells. We presume that interposing a C60/LiF layer at the interface could repair the poor contact at the electron acceptor/cathode interface and improve the charge career extraction from the BHJ.

Nanostructure thin films and sandwich devices of palladium phthalocyanine (PdPc) and chloro-aluminum-phthalocyanine (ClAlPc) were prepared by thermal evaporation technique. Optical and struc- tural properties of nanostructure thin films were investigated by XRD, SEM and optical absorption. The SEM images demonstrated PdPc (40–60 nm) and ClAlPc (30–50 nm) nanostructures. XRD pat- terns showed that thin films are in α-phase at room temperature. Also, optical bandgap energy of thin films was calculated by optical absorption spectra. Heterojunction (Au|PdPc|ClAlPc|Al) and single layer (Au|PdPc|Al and Au|ClAlPc|Al) devices were fabricated. Electrical measurements demonstrated the semi-conducting and photo-conducting behavior of thin films. After that, devices were exposed to different concentrations of O2 at 300 K and 350 K and conductivity of thin films was increased on exposure to O2 . Heterojunction devices were more sensitive than other thin films and had better response and reversibility in comparison with single layer devices at 350 K. Finally, 10% O2 was mixed with different percentages of relative humidity and all results showed that the conductivity of thin films is reduced on exposure to O2 mixed to humidity.

Thin films of a (Se80Te20)100−xAgx (1 ≤ x ≤ 4) were prepared by vacuum evaporation technique in a base pressure of 10−5 mbar onto well-cleaned glass substrates. The photoconductive measurements have been carried out on (Se80Te20)100−xAgx (1 ≤ x ≤ 4) thin films at different intensities 0–1200 lx in the temperature range 263–333 K. Dark conductivity (σd) and photoconductivity (σph) increase but the activation energy decreases as Ag concentration increases in the present glass composition. The measurements of intensity dependence of photoconductivity show that the photoconductivity increases with intensity as a power law where the power is found to be between 0.5 and 1.0. The photosensitivity (σph/σd) decreases with increase in Ag concentration. The results are explained on the basis of increase in the density of the localized states.

A very large surface to volume ratio of nanoporous silicon (PS) produces a high density of surface states, which are responsible for uncontrolled oxidation of the PS surface. Hence it disturbs the stability of the material and also creates difficulties in the formation of a reliable electrical contact. To passivate the surface states of the nanoporous silicon, hydrocarbon films prepared by plasma enhanced chemical vapor deposition of methane (PECVD) have been deposited on porous silicon (PS). Conduction properties as well as optical characteristics of the as-deposited samples and annealed ones have been studied by current-voltage (I-V) and capacitance-voltage (C-V) measurements, spectral response, ellipsometry and Fourier transform infrared spectroscopy (FTIR) as a function of the annealing temperature, ranging from 200 to 750 °C. By high-temperature treatment, the low rectifying I-V curves become strong rectifying and C-V curves are similar to those of metal-insulator-semiconductor structures. These characteristics were explored and can be appropriately used in the fabrication of optoelectronics and sensor devices based on PS.

Local order changes determined in an aluminosilicate matrix by calcination and addition of iron, yttrium or dysprosium oxides were investigated by X-ray diffraction and infrared spectroscopy. The nanocrystalline phase is reached only by Fe doping and not by the other two dopings. After calcination at temperatures as high as 1200 °C, nanocrystalline cristobalite alone is formed in the aluminosilicate matrix, while the doped samples favor the additional growth of mullite and quartz nanocrystals. The aluminosilicate spinel phase was not detected in any of these samples. An additional crystalline phase was only observed in the samples doped with yttrium and dysprosium. The structural units evidenced by FTIR analysis are associated with the crystalline phases identified by X-ray diffraction.

The interfacial magnetoelectric (ME) effect in ferromagnetic-ferroelectric (FM-FE) tunneling junctions was investigated in this work. We found that the tunneling magnetoresistance (TMR) changes with the reversing of the electric polarization of the FE barrier. The theoretical results also indicated that TMR is strongly dependent on the electric polarization, the exchange splitting energy, the screening lengths in the electrodes, and the dielectric constant of the FE barrier layer. These results may provide some insights into switching magnetization electrically for spintronics and presenting independent tunneling states in a single junction for multi-value storage memory applications.

Laser-induced breakdown spectroscopy (LIBS) was applied to the quantitative analysis of elemental composition of soil. The experiment was performed in air at atmospheric pressure and at room temperature. A Nd:YAG laser with the fundamental wavelength of 1064 nm was employed to generate the soil plasma. The emission spectra from the plasma were collected by the Cerny-Turner type of spectrometer, which was equipped with an intensified charge-coupled device (ICCD). The plasma temperature and electron density were evaluated by the Boltzmann plot method and the Saha-Boltzmann equation respectively. Then the concentrations of elements in soil were further obtained by the internal standard of iron element and some selected atomic/ionic lines. In order to prove the credibility and reliability of the present LIBS results, a comparison between the LIBS results and the nominal concentrations was performed. It was found that the LIBS results agree with the nominal concentrations. Therefore the LIBS technique promises to fast and in simultaneous multi-element quantitative analysis of soil.

An atmospheric pressure plasma source supplied by an electrical circuit consisting of two voltage sources in parallel connection is reported. One of them is a low-power self-oscillating flyback converter which produces negative voltage pulses with an amplitude of several kilovolts. The high voltage pulses are necessary to ignite an electrical discharge between the electrodes at atmospheric pressure. An additional dc source delivering several hundreds of volts at a few hundred milliamps is used to sustain the electrical discharge. The circuit configuration allows the control of the discharge current over a wide range, in a simple manner. By using argon as a working gas, a stable plasma plume up to 8 mm long can be obtained either in a transferred or non-transferred arc mode.

Research and development activities in organic solar cells have been intensified in the last two decades, and the reported energy conversion efficiency in small cell samples is rapidly increased. However, the relation between cell performance and material preparation conditions is not fully understood. In this work charge carrier recombination processes in hybrid poly-3-octylthiophene (P3OT)/cadmium sulfide (CdS) photovoltaic cells were analyzed as a function of structural and optoelectronic properties of chemical bath deposited CdS thin films. The temperature of the bath solution varied between 60 and 80 °C, and the deposition time from 1 to 3 h. Charge carrier recombination times in CdS films were measured with photoconductance decay technique, whereas the same time in P3OT films was estimated by Time-of-Flight method. Charge carrier recombination rates at CdS/P3OT interface were determined by transient photovoltage technique. It is found that CdS films grown at lower solution temperature (60 °C) give a higher charge carrier recombination rate at CdS/P3OT interface and larger short-circuit current density and energy conversion efficiency values in the corresponding solar cells, in comparison with the 80 °C deposited ones. This improvement could come from the reduction of charge carrier trap density inside grains as well as at grain boundaries in lower temperature deposited CdS films.

Backside sample preparation is a well-known method to help circumvent undesired effects and artifacts in the analysis of a sample or device structure. However it remains challenging in the case of thin layers analysis since only a fraction oRelax;f the original sample must remain while removing most or all of the substrate and maintaining a smooth and flat surface suitable for analysis. Here we present a method adapted to the preparation of ultrathin layers grown on pure Si substrates. It consists in a mechanical polishing up to a few remaining microns, followed by a dedicated wet etch. This method can be operated in a routine fashion and yields an extremely flat and smooth surface, without any remaining Si from substrate. It therefore allows precise analysis of the layers of interests with various characterization techniques.

Understanding how high-intensity compression waves damage human tissue is critical to developing improved therapeutic interventions for treating traumatic injuries arising from explosive devices. Assessment of the cellular and molecular basis of damage that is physiologically relevant requires the study of biomaterials using appropriate techniques which subject samples to compression waves at magnitudes relevant to traumatic injury. Here, we present the design and initial calibration of a polycarbonate chamber to be used in a split Hopkinson pressure bar system to study live cell cultures.

The Schottky barriers formed at the interface between gold and various rare earth doped GaN thin films (RE = Yb, Er, Gd) were investigated in situ using synchrotron photoemission spectroscopy. The resultant Schottky barrier heights were measured as 1.68 ± 0.1 eV (Yb:GaN), 1.64 ± 0.1 eV (Er:GaN), and 1.33 ± 0.1 eV (Gd:GaN). We find compelling evidence that thin layers of gold do not wet and uniformly cover the GaN surface, even with rare earth doping of the GaN. Furthermore, the trend of the Schottky barrier heights follows the trend of the rare earth metal work function.

C38 carbon steel has been nitrided by radiofrequency cold plasma discharge with the aim to study the effect of gas composition on structural and mechanical properties of nitrided substrates. The plasma nitriding was carried out on unheated substrates, using two different gas mixtures (75% N2/25% H2 and 25% N2/75% H2) for 8 h of plasma treatment. Electron Probe Microanalysis (EPMA) showed that the nitrogen content and the nitride layer thickness mainly depend on the hydrogen content in the plasma. For 75% N2/25% H2 mixtures, nitrided samples showed the formation of thicker nitride layer with high content of nitrogen compared to those formed in the case of 25% N2/75% H2 or pure N2 . The thickness of the nitride layer formed is approximately 15 μm for 8 h of plasma with 75% N2/25% H2 . X-ray photoelectron spectroscopy (XPS) was employed to obtain chemical-state information of the plasma- nitrided steel surfaces. The mechanical properties of plasma-nitrided C38 steel were investigated by Vickers microhardness measurements. The micromechanical results show the formation of a new hard layer on the surface after N2/H2 treatment plasma and it reaches a maximum value of more than 2242 HV0.005 for 75% N2/25% H2 plasma-nitrided samples. However, a decrease in the hardness values with the applied load has been evidenced.

Growth of thin layers of compound semiconductors such as GaAs and Alx Ga1−x As was obtained by Liquid Phase Epitaxy (LPE) at 838–828 ° C in thickness range of 0.1–4.3 μm which was estimated by Scanning Electron Microscopy (SEM). By Secondary Ion Mass Spectroscopy (SIMS) measurements, type of impurity atoms and their density and uniformity with respect to thickness were measured. In this way we are sure that variation of impurity atoms such as Si, Te, Sn and Ge indicates that epilayers were formed uniformly and it demonstrated that the LPE growth was a suitable way to obtain a good quality of epitaxy layers. Amount of composition parameter x in the compound semiconductor AlxGa1−xAs was measured which varies from 0.13 to 0.4. In-depth profiles of SIMS indicated that Al atom can be replaced by Ga atom in the GaAs crystalline structure.