Defect and Diffusion Forum Vols. 297-301

Abstract: The results of the dynamic neutron radiography studies on drying of wet kaolin cylinders in the forced warm air flow are presented. The sample shrinkage and loss of water during drying was analyzed in terms of the brightness of registered neutron radiographs, and sample mass and temperature. The water saturation of the sample with water was discussed in comparison to the changes in local neutron effective macroscopic cross section. The neutron radiography results reveal more details of the drying process than gravimetric measurements indicating nonuniform distribution of water within samples. The obscuring effect of the scattered neutrons on the determination of the water content is discussed on the basis of the MC simulations results.

Abstract: Variable charge molecular dynamic simulations have been performed to study the diffusion mechanisms of oxygen atoms (O) in nickel (Ni) in the temperature range 950-1600 K and the very first steps of oxidation of monocrystalline nickel surfaces at 300 K and 950 K. The oxygen diffusivity can be well described by an Arrhenius law over the temperature range considered. The oxygen diffusion coefficient has been analysed and values of Ea = 1.99 eV for the activation energy and D0 = 39 cm2.s-1 for the pre-exponential factor were obtained. The first steps growth of the oxide layer show that after the dissociative chemisorption of the oxygen molecules on nickel surface, the oxidation leads to an island growth mode as observed experimentally.

Abstract: The growth of a U3O7 oxide layer during the anionic oxidation of UO2 pellets induced very important mechanical stresses due to the crystallographic lattice parameters differences between UO2 and its oxide. These stresses, combined with the chemical processes of oxidation, can lead to the cracking of the system, called chemical fragmentation. We study the crystallographic orientation of the oxide lattice growing at the surface of UO2, pointing to the fact that epitaxy relations at interface govern the coexistence of UO2 and U3O7. In this work, several results are given: - Determination of the epitaxy relations between the substrate and its oxide thanks to the Bollmann’s method; epitaxy strains are deduced. - Study of the coexistence of different domains in the U3O7 (crystallographic compatibility conditions at the interface between two phases: Hadamard conditions). - FEM simulations of a multi-domain U3O7 connected to a UO2 substrate explain the existence of a critical thickness of U3O7 layer.

Abstract: In this paper, we present a new Photothermal Deflection Technique (PTD) to determine thermal properties of bulk doped or undoped semiconductor such as GaAs, GaSb, InAs, etc. The method proposed here consists in covering the sample with a thin graphite layer in order to increase the photothermal signal and to ovoid any reflection on the sample surface. This method deals with the analysis of the logarithm of amplitude and phase variation of the photothermal signal versus square root modulation frequency where the sample placed in air is heated by a modulated light beam coming from a halogen lamp. So the best coincidence between experimental curves and corresponding theoretical ones gives simultaneously the best values of thermal conductivity and thermal diffusivity of the sample. These obtained values are in good agreement with those found in literature. The advantage of applying this method in this way lies in its simplicity and its sensibility to both thermal conductivity and thermal diffusivity.

Abstract: Sulfosalt SnSb2S4 films have been deposited on glass substrates by thermal evaporation and subsequently thermally annealed in vacuum at temperatures from 100 to 250°C. Below a transition temperature of 140°C, the films are highly resistive with a dominant amorphous component, however above this temperature, the samples exhibit p+-type semiconductor behaviour with a dominant crystalline component.In this work we have studied the thermal and optical properties of these films using the photothermal deflection technique. The thermal properties are determined by comparing the experimental amplitude and phase curves variations versus square root modulation frequency of the photothermal signal to the corresponding theoretical ones. The best theoretical fitting curves are obtained for well-defined values of thermal conductivity and thermal diffusivity. The optical absorption spectrum is obtained by comparing the experimental normalized amplitude of the photothermal signal curves variations versus the wavelength to the corresponding theoretical curves variations versus the optical absorption coefficient. We have determined the energy gap by using the Tock law. From a measure of the sample’s resistance, one can deduce the electrical resistivity which may be correlated to the thermal conductivity.

Abstract: In this work we describe a method based on the Photothermal Deflection Technique adapted for the determination of thermal properties of thin semiconductor layers deposited on a glass substrate. The sample placed in air is heated thanks a modulated pump uniform beam coming from a halogen lamp. The thermal conductivity and the thermal diffusivity are obtained by comparing the amplitude and phase variations versus square root modulation frequency between the experimental curves and the corresponding theoretical ones. The best coincidence permits to deduce the thermal properties of the sample.

Abstract: In this investigation, we focused on the effects of pressure on the melting of elements Cu, Pd as well as Pd3Cu order alloy. We have performed molecular dynamics based computations of the variation of the physical properties of the elements Cu, Pd and Pd3Cu alloy with pressure and temperature. The quantum Sutton-Chen many-body interatomic potentials have been used for these elements, and the standard mixing rule has been used to obtain the parameters of this potential for the alloy state. This molecular dynamics simulation was performed in the NPT ensemble. Our study enabled us to predict the thermodynamic properties such as melting temperature, isobaric heat capacity as well as the lattice thermal expansion. The temperature dependence of energy and density were calculated at high pressure. Moreover, we presented the variation of the melting temperature, heat capacity as well as the thermal expansion of the crystal with pressure. The obtained results showed that the melting temperature increase with increasing pressure and isobaric heat capacity as well as lattice thermal expansion decrease with increasing pressure. Our computed results are in reasonable agreement with the experimental data where they are available.

Abstract: Nowadays, the most promising methods for high purity hydrogen production are membranes separation such as polymer, metal, ceramic and composites. It is well known that Pd and Pd-alloys membranes have excellent properties for hydrogen separation. However, it has hydrogen embrittlement and high cost for practical applications. Therefore, most scientists have studied new materials instead of Pd and Pd-alloys. On the other hand, TiN powders are great in resistance to acids and chemically stable under high operating temperature. In order to get specimens for hydrogen permeation, the TiN powders synthesized were consolidated together with pure Co powders by hot press sintering. During the consolidation of powders at HPS, heating rate was 10K/min and the pressure was 10MPa. It was characterized by XRD, SEM, and BET. Also, we estimated the hydrogen permeability by Sievert's type hydrogen permeation membrane equipment.

Abstract: This study presents the influences of dye doping and hole blocking layer insertion on the electroluminescent properties of the blue organic light emitting diode. The luminance of the device was significantly improved by BCzVB doping because of the utilization of effective Förster energy transfer and the improvement of carrier injection and trapping; a BCzVB dominant emission was observed. Furthermore, when a BCP layer was inserted between the TBADN:BCzVB and Alq3 layers, a thin BCP layer insertion enhanced the injection of electrons and improved the luminance of the device. In contrast, a thick BCP layer insertion caused a delay in electron transport, resulting in a decrease in current density and a deterioration in luminance.

Abstract: There are several kinds of methods in improving the efficiency of organic light emitting diodes (OLEDs). In this work, we used a co-deposited hole blocking layer to improve the efficiency of OLEDs. The structure of the component is: ITO/ MTDATA(15 nm) /NPB(40 nm) /BCP(10 nm) /BCP: Alq(15 nm) /LiF(0.7 nm)/ Al(180 nm). We changed the mixing rate of the BCP:Alq layer to be capable of hole blocking and electron transporting, and then improved the efficiency of OLEDs. Finally, we prepared white light OLED with doping Rubrene in NPB. When the concentration of the NPB: Rubrene layer was 2.0 wt.%, the device could emit the white light at 100 mA/cm2, and the luminance was above 2300 cd/m2, and the color coordinate was x = 0.36, y = 0.37.