The structural and thermodynamic properties of tetragonal-TiH2 under high temperatures and pressures are investigated by Ab initio calculations based on pseudo-potential plane-wave density functional theory method within using the generalized gradient approximation (GGA) and quasi-harmonic Debye model. Some ground state properties such as lattice constants, bulk modulus and elastic constants are good agreement with the available experimental results and other theoretical data. Through the quasiharmonic Debye model, in which the phononic effects are considered, the thermodynamic properties of tetragonal-TiH2 such as thermal expansion coefficient, Debye temperature, heat capacity and Grüneisen parameters dependence of temperature and pressure in the range of 0–1000 K and 0–10 GPa are also presented, respectively.

This paper reports on the temperature dependent threshold voltage analysis of AlGaN/GaN High electron mobility transistors (HEMTs) in order to investigate the trap effects occurring in these devices. Measurements are performed in pulse configuration to emphasize the gate-lag and drain-lag effects involving current collapses. A quantitative extraction of the interface traps density is performed through the observation of the pinch-off voltage shifts in cold bias conditions. Additionally, a thermally activated energy level of 0.25 eV is evaluated whatever the bias condition. It is also shown that the trap density increases drastically when the drain is biased, limiting the performance of AlGaN/GaN devices through drain-lag effect.

Polycrystalline Ba8Ga16MgxGe30−x compounds were synthesized by combining solid-state reaction with spark plasma sintering (SPS) method. The structural and electronic properties of Mg-substituted Ge type-I clathrate phase Ba8Ga16MgxGe30−x (x = 1, 2, 3, 4) were investigated experimentally and theoretically. Theoretically structural and electronic properties of Ba8Ga16MgxGe30−x were calculated by first-principles method based on the density-functional theory. The results indicate a strong preference for the occupation of the 6c sites by Mg. It is found that Mg substitution for Ge can lower the melting points and bulk modulus of this system. The formation energies and the binding energies decrease with increasing Mg content, suggesting that the Mg-doped Ba8Ga16Ge30 clathrates are stable in a limited range of composition. The calculated results show that these alloys are all indirect gap semiconductors and the values of band gap increase with the increase of Mg content. All specimens exhibit the behavior of the p-type conduction, which is originated from the presence of a shallow acceptor energy level. The electrical conductivity and the room-temperature carrier mobility decrease with increasing Mg content, while the room-temperature carrier concentration increases with increasing Mg content.

We investigated the electrical conduction and resistance switching mechanisms of TiOx thin films grown on three kinds of bottom electrode at room temperature (an inert Pt, an active Ti and fluorine tin oxide FTO electrodes). The bottom electrode materials strongly affect the I-V characteristics and switching parameters. The I-V characteristic is explained through the presence of interface states in the metal electrode devices (Pt and Ti) and the work function in the metal oxide device (FTO). The Pt device has the smallest VSET and largest switching ratio, while the Ti device shows the largest VSET and smallest switching ratio. XPS data shows non-lattice oxygen in TiOx films. Therefore, the proposed bipolar resistance switching arises from formation and rupture of filament paths, generated by the movement of oxygen vacancies. All devices depict the same electrical conductions, trap-controlled space-charge-limited, FN tunneling and Ohmic conductions for a high resistance state and a low resistance state, respectively. In this study, the rarely reported FN tunneling conduction in published TiOx-based ReRAM device was found, which can be attributed to an influence of the bottom electrode on the electronic distribution in devices.

Single crystals of urea-oxalic acid (UOA) have been grown from aqueous solution by slow evaporation technique. Single crystal X-ray diffraction analysis confirmed that the grown crystals belong to monoclinic system having space group P21/C. The presence of functional groups was confirmed by using Fourier transform infrared (FTIR) spectroscopy. Optical absorption studies show very low absorption in entire visible region and the UV cut-off is found to be around 240 nm. Thermal analysis studies were carried out using TG/DTA analysis and the grown crystal is thermally stable up to 180 °C. Dielectric constant studies confirm the ferroelectric property of the materials and very low dielectric loss reveals very high purity of the crystal.

In this work we studied both theoretically and experimentally interactions between zinc phthalocyanine (ZnPc) and selected gases (Ar, He, N2, O2, H2, NO2). Specifically, we focused on electrical conductivity as important macroscopical physical parameter reflecting ZnPc/gas complexes interaction states. To interpret the measured data and determine the main parameters that influence the resistivity/charge transport ability of ZnPc in a specific gas atmosphere, the density functional theory (DFT) has been used. Combining experimental results and DFT modeling we were able to characterize states/parameters influencing charge transport conditions from new and comprehensive perspectives.

CuInS2, CuIn3S5 and CuIn5S8 films were grown by thermal evaporation using oblique angle deposition technique. During the deposition, the substrate temperature was maintained at Ts = 150 °C and the deposition angle was fixed at α = 0° and 85°. The powders and thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). From the XRD data of powders, we calculated the lattice parameters of the structure for the different compounds. XRD patterns of thin films revealed that all samples deposited at α = 0° were polycrystalline. Indeed, CuInS2 and CuIn3S5 films had a chalcopyrite structure with preferred orientation along (1 1 2) while CuIn5S8 films exhibit a spinel structure with preferred orientation along (3 1 1). However, CuIn2n+1S3n+2 with n = 0, 1 and 2 films deposited at α = 85° were amorphous in nature. The surface and cross-section of the films were observed by AFM and SEM. The oblique angle deposition films showed an inclined columnar structure, with columns tilting in the direction of the incident flux. The surface roughness of the different films deposited, respectively, at α = 0° and 85° was determined by two methods (AFM and spectrophotometric analysis). The obtained values show an increase of the surface roughness by increasing the deposition angle α.

This letter focuses on the evolution under illumination of the minority carrier lifetime and conversion efficiency of p-type gallium (Ga) co-doped solar grade multicrystalline silicon wafers and solar cells. We present experimental data regarding the concentration of boron-oxygen (B-O) defects in this silicon when subjected to illumination, and the concentration was found to depend on [B]-[P] rather than [B] or the net doping p0([B] + [Ga] – [P]). This result implies that the compensated B is unable to form the B-O defect. Minority carrier lifetime and EQE measurements at different degradation states indicate that the B-O defect and Fe-acceptor pairs are the two key centers contributed to LID in this material.

Thin films of aluminum oxide of thickness 293–433 nm were grown on fused silica substrates by pulsed laser deposition (PLD) of an alumina target with KrF excimer laser radiation. The effects of oxygen background pressure (0.5–50 Pa) and substrate temperature of room temperature to 800 °C were investigated on thickness, crystal-structure, optical properties and thermal stability of alumina films. It was found that PLD grows a weakly crystalline aluminum oxide film at in situ substrate temperature of 800 °C and oxygen background pressure of 5 Pa. Post-deposition annealing studies of amorphous alumina sample prepared at in situ temperature of 600 °C found that crystallization starts at 800 °C and forms δ alumina phase.

X-ray photoelectron spectroscopy (XPS) and cathodoluminescence (CL) method have been employed to study the chemical composition and the oxygen vacancy concentration of HfO2, Sc2 O3 and (HfO2)1−x(Sc2O3)x films. It was found that the increase of Sc content led to monotonic decreasing the Hf4f7/2 and Sc2p3/2 binding energies indicating to form solid solution (HfO2)1−x(Sc2O3)x. All the samples characterized by the intensive CL spectra with maximum around 3 eV which originated due to some radiative recombination emission caused by oxygen deficiency. The concentration of oxygen vacancy in the Sc-doped HfO2 is sensitive to the Sc content and as a result the intensity of CL spectra of (HfO2)1−x(Sc2O3)x is lower that those of pure HfO2 and Sc2O3.

By combining the techniques of dielectric relaxation spectroscopy (DRS), measurement of both ac and dc conductivities, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), we have explored the effect of electrical ageing on poly (methyl methacrylate) (PMMA) films at temperature between 0 °C and 80 °C in the frequency range of 1 Hz–107 Hz. These results are discussed and correlated to FTIR and SEM observations.

Aluminum nitride is a ceramic compound with many technological applications in many fields, for example optics, electronics and resonators. Contaminants play a crucial role in the AlN performance. This paper focuses mainly in the effect of oxygen when AlN, with O impurities in its structure, is grown on oxidized layers. In this study, AlN thin films have been deposited at room temperature and low residual vacuum on SiO2/Si (1 0 0) substrates. AlN films were grown by DC reactive magnetron sputtering (aluminum target) and atmosphere composed by an argon/nitrogen mixture. Working pressure was 3 mTorr. Film characterization was performed by AES, XRD, SEM, EDS, FTIR, HRTEM, SAED and band-bending method. Our results show that oxidized interlayer imposes compressive stresses to AlN layer, developing a polycrystalline deposition. Indeed, when film thickness is over 900 nm, influence of oxidized interlayer diminishes and crystallographic orientation changes to the (0 0 0 2) one, i.e., columnar structure, and stress relief is induced (there is a transition from compressive to tensile stress). Also, we propose a growth scenario to explain this behaviour.

CdSe/ZnS quantum dots and gold nanoparticles have been grown in-situ onto the surface of carbon nanotubes. The nanohybrids were then, dielectrophoretically aligned between gold microelectrodes and the electrical response was investigated. The conductance of nanotube-quantum dot hybrid was found to be sensitive to incident white light. The electrical resistance of the carbon nanotube-quantum dot nanohybrid decreased from 1.9 × 104 Ω (in the dark) to 0.91 × 104 Ω after the impact of white light. The electrical resistance of the carbon nanotube-gold nanoparticle nanohybrid was calculated to be 1.86 × 103 Ω, which is much smaller than that of carboxylated carbon nanotubes (4.03 × 105 Ω). Such a modulation in electrical properties may enhance the use of carbon nanotubes in future nanoscale devices.

Al/MoOx nanoenergetic multilayer films (nEMFs) were deposited by magnetron deposition method. The samples with bilayer thicknesses of 75 nm and 225 nm were prepared, respectively, and the total thickness is 3 μm. The as-deposited Al/MoOx nEMFs were characterized with varied analytical techniques, including SEM, XRD, XPS and DSC. Results show that the MoOx films are amorphous, and are composed of MoO3, Mo2O5 and MoO2. The values of heat release in samples are 3524 J/g and 2508 J/g, respectively, and the final products are Mo, MoO2, and Al2O3. Finally, the reaction paths and reaction kinetics of Al/MoOx exothermic reactions were discussed.

Cd1−xZnxS thin films were deposited on the glass substrates (GS) and on the potassium permanganate activated substrates (KMAS) at 350 °C using spray pyrolysis technique. X-ray diffraction studies confirmed that the films are polycrystalline and belong to the hexagonal structure. Scanning electron microscopic studies revealed an effective change on the surface morphology of the film due to potassium permanganate activation (KMA). Transmittance spectra of Cd1−xZnxS thin films were recorded in the range of 320–700 nm and the transmittance was found to be high for the film coated on KMAS than GS. Photoluminescence spectra show a strong emission peak at 585 nm for the film coated on the GS and it is shifted to 592 nm for the film coated on KMAS. Thus the results authenticate that KMA influences the structural and optical properties of the deposited films.

A Cu2ZnSnSe4 (CZTSe) thin film fabricated by selenization of stacked pure metal precursors through e-beam evaporation on Mo-coated soda lime glass substrates worked as thin film solar cell absorber. The selenization was carried out under element Se vapor circumstance at 570 °C for 20 min. The absorber went through chemical bath CdS deposition, sputtered ZnO, ITO and Al electrodes to become a solar cell. Unlike previous works, only simple three-layer metal precursors without any compound were used as evaporation sources. The synthesized CZTSe absorber layer phase was identified by X-ray diffraction. The solar cells were measured by AAA class solar simulator. The absorber layer thickness was measured by scanning electron microscope (SEM). Energy dispersive spectrometer (EDS) was also used for checking metal ratios in the absorber layer. The best efficiency was 4.2%. In this work, we found that there were voids in absorber film bottom. The Cu-top precursors will lead to larger grains, flatter surfaces and larger voids than Sn-top precursors. The Cu-top precursor may also contribute to better selenization which may help prevent Zn loss but cause Sn loss. Finally, this work also showed Cu-poor and Zn-rich will improve conversion efficiency.

Fe doped ZnO thin films with various levels of iron doping concentration (0, 1, 2, 3 at.%) content were produced by sol-gel dip coating method. The influence of Fe doping on the structural, morphological and optical properties of ZnO thin films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with the hexagonal structure. Scanning electron microscope has indicated that crystallites dispersion in the films is generally homogeneous and the particle morphology changes with increase in the doping concentration. FTIR measurements show that the intensity of Zn-O band increases with increasing doping concentration and the UV-visible transmittance results show a high transparency in the visible range. The room temperature photoluminescence (PL) spectra of Fe doped ZnO indicate that the green-orange emission decrease with increasing Fe doping.

In this paper, experimental results on the influence of the substrates of different refractive index on the optical properties of two-dimensional silver nanoparticle array are presented. It is shown that plasmon mode that arises from cooperative interactions between closely spaced nanoparticles exhibit different dependences on the incident angle of light. Those dependencies can be qualitatively explained by the concept of mirror images induced in a substrate. Semiconductor (ITO) substrate possesses higher refractive index which even more affects the optical response of silver nanoparticle array.

The aim of our work is to obtain nano-structured cadmium oxide (CdO) thin films by sol-gel spin coating method and to investigate the effects of cadmium sulfide quantum dots (CdS QDs) doping on the structural modification and surface morphology evolution. X-ray diffraction (XRD) results show that the intensities of the peaks of the crystalline phase increase with the increase in CdS QDs concentrations. From scanning electron microscopy (SEM) images, the distinct variations in the morphology of the thin films were also observed. In addition, the evolution of surface morphology, roughness and granularity has been characterized by atomic force microscopy (AFM). Moreover, we have performed the optical characteristics of the thin films such as transparency, energy band gap and Urbach tail. The optical band gap of the thin films increases from 2.23 to 2.51 eV with the increase in CdS QDs concentrations due to the Moss–Burstein effect. The enhanced values of the transparency, energy band gap and crystallity indicate that addition of CdS QDs can be used to modify the optical, structural and morphological properties of CdO thin films.

Improvements in technologies and the growing security needs in airport terminals lead to the development of non destructive testing devices using terahertz waves. Indeed, these waves have the advantage of being, on one hand, relatively penetrating. They also have the asset of not being ionizing. It is thus potentially an interesting contribution in the non destructive testing field. With the help of the VISIOM Company, the possibilities of this new industrial analysis method in assisting the restoration of works of art were then approached. The results obtained within this framework are presented here and compared with those obtained by infrared thermography. The results obtained show first that the THZ method, like the stimulated infrared thermography allows the detection of delamination located in murals paintings or in marquetries. They show then that the THZ method seems to allow detecting defects located relatively deeply (10 mm) and defects potentially concealed by other defects. It is an advantage compared to the stimulated infra-red thermography which does not make it possible to obtain these results. Furthermore, they show that the method does not seem sensitive to the various pigments constituting the pictorial layer, to the presence of a layer of “Japan paper” and to the presence of a layer of whitewash. It is not the case of the stimulated infrared thermography. It is another advantage of the THZ method. Finally, they show that the THZ method is limited in the detection of low-size defects. It is a disadvantage compared to the stimulated infrared thermography.