Organic field-effect transistors (OFETs) with a pentacene/TPBi/pentacene sandwich structure were realized and characterized. Compared with the single pentacene layer transistors, these devices not only showed an obvious reduction of threshold voltage but also presented a significant enhancement of field-effect mobilities. The performance improvement was attributed to the high conductivity of the sandwich active layers, which were analyzed by applying the transfer line method. Meanwhile, the morphologies of pentacene films with and without the TPBi interlayer were characterized by atomic force microscopy, the smoother surface of the upper pentacene film was observed in pentacene/TPBi/pentacene. Moreover, by applying X-ray diffraction, a higher-order growth phase of the pentacene thin film was observed.

Surfaces that exhibit reversible wettability toward water are extremely important for a variety of technological applications. In this context, the development of superhydrophobic and superhydrophilic surfaces for self-cleaning applications has been receiving a great deal of attention in the last few years. In this review, an overview of the current state-of-science and technology of self-cleaning surfaces is presented. The current understanding of physics of wetting leading to surfaces with predictive, controllable and reversible wettability is first presented. The review then focuses on materials, mainly metal oxides and their composites, employed for self-cleaning applications. It is shown that, although conventionally oxides and polymers are considered for self-cleaning applications, recent developments point toward the use of artificially engineered surfaces with hierarchical roughness. Applications of self-cleaning films in non-conventional areas such as protection of fabrics, solar cells and structures related to cultural heritage are discussed. The review ends with an outlook for the future in terms of science and technology of self-cleaning surfaces.

It has been systematically investigated about the magnetic properties of the composite and single-phase SrFe12O19 prepared with the precursor of different Fe3+/Sr2+ molar ratios of 12:1, 11:1 and 10:1, respectively. With increasing the calcinations temperature, the coercivity of all samples decreases which can be determined by the stress model. The δm(H) results indicate that the intergrain exchangecoupling interaction exists both in composite and in single-phase SrFe12O19, resulting in the remanence magnetization enhancement, and the magnetostatic interaction become dominant in the samples with higher calcinations temperatures. The irreversible susceptibilities χirr(H) curves show that there may exhibit the exchange-spring behavior in the composite SrFe12O19 with more soft magnetic γ-Fe2O3, and the irreversible switching field may be qualitatively used to determine the coercivity magnitude.

Linear, ring and 3D structures of (ZnTe)n clusters for n = 2–6 are completely optimized using B3LYP/LanL2DZ basis set. The stability, dipole moment and point group for linear, ring and 3D structures are studied. The stability of the clusters is found to increase with the increase in the cluster size. The dipole moment of the cluster depends upon the asymmetry of the atoms in the structure. The HOMO-LUMO gap, electron affinity, ionization potential and stability factor of different isomers for these different structures are also compared and studied. From the observed studies it is found that the electronic and chemical properties are influenced by the electron affinity and HOMO-LUMO gap. The calculated parameters and the results of different structures will provide clear information to fabricate a new material that has commercial importance in the thin film solar cells and optoelectronic devices.

A high-precision printing and patterning carbon nanotube (CNT) cathode was prepared using the screen-printing method. Selective plasma etchings were introduced to improve field emission properties of the CNT cathode through the reactive ion etching (RIE) system. The field emission characteristics and mechanism of the cathode after etching treatment were studied. It was found that the reactive ion etching could effectively expose plentiful CNTs inside the cathode and protrude them from the surface. Moreover, with the increase of RIE operation pressure, CNT cathode field emission behavior changed from metal-insulation medium-vacuum (MIV) to a classical metallic-microprotrusion (MM) structure field emission model. The results showed that only the cathode with appropriate RIE operation pressure etching has a low operation field and a high emission current density.

X-ray diffraction (XRD) patterns indicated that the powder of 4-tricyanovinyl-N,Ndiethylaniline (TCVA) has a polycrystalline structure with triclinic crystal system. The scanning electron microscope of the as deposited TCVA thin film shows a nanocrystalline structure with crystallite size of 45–75 nm. The crystallite size increases by increasing film thickness and annealing temperatures. The dark electrical resistivity decreases with increasing film thickness. Such variations are a consequence of crystallite size effect on the electrical resistivity of the films. The conductivity of the films measured in air is high in comparison to those measured under vacuum by one order. The removal of the hydroxyl group states by evacuation decreased the electrical conductivity of TCVA films. The temperature dependence of the electrical conductivity of TCVA films shows that the conduction is through a thermally activated process having two conduction mechanisms. The average values of activation energies are 0.28 and 0.74 eV for extrinsic and intrinsic conduction mechanisms, respectively. H-O group adsorption is responsible for the extrinsic conduction in TCVA films.

In this work we present a theoretical and mathematical relationship which calculates the site reaction probability (SRP) of the sticking on (Si-) dangling bonds (DB) or the SRP to abstract H from (Si-H) bonds, on the a-Si:H surface. The results are in agreement with those obtained by the Monte Carlo simulation. Using these probabilities allowed us to compute the surface reaction probability of SiHx radicals on a-Si:H for several values of the temperature. The surface reaction probability (SFRP) results show also an excellent agreement with other works found in the literature.

In this work, pressure-induced phase transition and elastic properties of BeS II–VI compounds semiconductor are investigated by first-principle method. Phase transition of BeS from direct gap semiconductor phase (ZB) to indirect-gap semiconductor phase (RS) occurs at 51.45 GPa accompanied by 11.23% volume collapse. Phase transition is due to S atom’s weakened electron attraction. Once the shared charge center of shared electron reaches 0.58 of the distance between Be and S, will the phase be unstable. Moreover, the broadened anti-bonding state and reduced bonding state display that tetrahedral Be-S covalent bonds are weakened. And then, the ZB structure is destroyed and rebuilt to RS structure. Furthermore, changes of covalent bond would cause evident variation of elastic constants and shears on {1 0 0} and {1 1 0} planes.

We present a novel multilayered architecture for memristive devices which provides an alternative to conventional conductive filament switching. In conventional resistive switching, conductive filaments form and extend stochastically under applied electrical bias, with longer filaments being subjected to magnified electric fields that amplify their growth rate, producing a spatially localized and highly non-uniform conduction front of filaments. This produces devices with large variations in resistive and capacitive properties that are difficult to tune. Here, we simulate a multilayered device structure with alternating ionic mobility that predicts the development of a quasi-uniform conduction front which amplifies memcapacitive properties of the device and reduces device-to-device variability. Furthermore, this novel structure is predicted to enable fine-tuned control of switching events, an important property for analog (multibit) memory and neuromorphic computing applications.

The reverse leakage current mechanisms of Schottky diodes prepared using liquid gallium on as-grown and cleaved tungsten diselenide surfaces were investigated by current-voltage method for the first time. The major leakage mechanism has been identified as tunneling current along with a small contribution of thermionic emission current. The leakage tunneling current is found to be predominant in uncleaved diode compared to that in cleaved one. This is related to the magnitude of interface state density and interfacial inhomogeneities. The inhomogeneous nature of the interface of the fabricated diodes is ascribed to be the reason behind its soft reverse characteristics.

For the first time, thin-film CIGS solar cells have been fabricated by co-evaporation on specially developed non-conducting perlite (an aluminum potassium sodium silicate natural mineral of volcanic origin) glass-ceramic substrates to develop a fully integrated photovoltaic and building element. Such glass-ceramic material can meet the physical requirements to solar cells substrates as well as the cost goals. The preliminary data presented show that CIGS solar cells deposited on ceramic substrates can exhibit efficiency higher than 10%.

In the present work, ZnO and ZnO:Cu thin films with c-axis preferred orientation were prepared on porous silicon, silicon and glass substrates by radio frequency magnetron sputtering technique. X-ray diffraction measurements revealed that the particle size of all samples was in the range of 11.41 ~ 17.67 nm. All the samples exhibited a compressive stress. Fourier transform infrared spectroscopy showed the presence of Si-O-Si stretching appeared at 1067 cm–1, which was assigned to the transverse optical mode of the asymmetric vibration. The E2 (high) mode indicated that the residual stress was observed in the Raman spectra. The optical transmission and absorption spectra were studied, indicating that the optical band gap value shifted to a longer wavelength after Cu doping. Effect of substrate material and Cu doping on the photoluminescence properties of ZnO thin films, along with the origin of some emission peaks, was discussed in detail. The experiment results indicate that the ZnO and ZnO:Cu thin films grown directly on the Si substrates have a high quality of crystallization and intense blue luminescent properties.

The AlGaN/GaN/InGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) sample has been grown by MOCVD on (0 0 0 1) sapphire substrate. The structure features a 7 nm In0.046Ga0.954N interlayer determined by Rutherford backscattering (RBS). Since the polarization field in the InGaN interlayer is opposite to it in the AlGaN layer, an additional potential barrier is introduced between the two-dimensional electron gas (2DEG) channel and buffer, leading to enhanced carrier confinement and improved buffer isolation. The GaN layers between the AlGaN layer and InGaN interlayer are divided into two layers consisting of GaN channel layer which provides high mobility 2DEG grown at 1070 °C and GaN spacer layer grown at the same temperature as InGaN interlayer (800 °C) to prevent indium diffusion. RBS measurement confirms that the 3 nm GaN spacer layer isolates the InGaN interlayer well and free from diffusion. Hall measurement has been performed, the mobility as high as 1552 cm2/V s at room temperature is obtained and the sheet carrier density is 1.55 × 1013 cm−2. The average sheet resistance is 331 Ω/sq, respectively. The mobility obtained in this paper is about 20% higher than similar structures reported.

In this paper the set of photoelectromagnetic methods for determination of recombination and diffusion parameters of charge carriers in p-type mercury cadmium telluride epitaxial thin films at temperature range 77–125 K is offered. The set of methods includes the photoconductivity in magnetic field for Faraday and Voigt geometries, the photoelectromagnetic effect, the Hall effect and the measurements of magnetoconductivity. Such films parameters as concentrations and mobilities of heavy and light holes, mobility of minor electrons, electrons lifetime and ratio between holes and electrons lifetimes, surface recombination velocities can be determined with help of offered set.

We present in this work a contribution to the study of the solid solution (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3. Room temperature X-ray diffraction patterns for some prepared compositions confirmed the formation of perovskite structure. The study of the evolution of dielectric properties as a function of sintering temperature allowed us to determine the optimum conditions that minimize the presence of defects and oxygen stoichiometric limit fluctuations due to the volatility of bismuth. The variation of permittivity as a function of temperature and frequency for the (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3 solid solution was measured. The effect of Ba0.7Na0.3Ti0.7Nb0.3O3 addition content on crystal structure, dielectric and magnetic properties of BiFeO3 was investigated. Raman measurements reveal resonant enhancement of two-phonon excitation for (1 – y)BiFeO3/y(Ba0.7Na0.3Ti0.7Nb0.3)O3 samples. We also expect that the solid solution shows weak ferromagnetic behavior for low Ba0.7Na0.3Ti0.7Nb0.3O3 levels of substitution.

Samples from sheets of the polymeric material polyester have been exposed to X-rays from a 50 kV X-ray tube in the dose range 10–100 kGy. The resultant effect of X-rays has been investigated using different techniques such as X-ray diffraction XRD, thermogravimetric analysis TGA, differential thermal analysis DTA and stress-strain measurements. The results indicate that the polyester decomposes in one weight loss stage. Also, the X-ray irradiation in the dose range 30–100 kGy led to a more compact structure of polyester, which resulted in an improvement in its thermal stability. The variation of transition temperatures with the X-ray dose has been determined using DTA. The polyester thermograms were characterized by the appearance of an endothermic peak due to the melting of the crystalline phase. The melting temperature of the polymer Tm was investigated to probe the crystalline domains of the polymer. At the dose range 30–100 kGy, the defect generated destroys the crystalline structure, thus reducing the melting temperature. In addition, the stress-strain measurements indicate that the X-ray irradiation at the same dose range 30–100 kGy yields crosslinked polyester of high resilience that is suitable for manufacturing protective clothes that reduce heat stress.

The possibilities for extracting chemical composition-related information from a singlewavelength X-ray reflectometry experiment are investigated. It is shown that the X-ray absorption of certain elements is sufficient to cause a significant effect on the reflectivity curve, which can be in turn exploited to determine its abundance in the thin film. The limitations are discussed using simulated data and the methodology is applied for the determination of the iodine concentration in iodine-treated thin polyaniline films. More generally the method appears to be very sensitive for the non-destructive determination of the weight percentage of metal nanoparticles in thin polymer films.

Glassy samples of Se78−xTe20Sn2Pbx (0 ≤ x ≤ 6) system are prepared by melt quenching method. For non-isothermal study of crystallization kinetics, DSC scans have been taken at the heating rates 5, 10, 15 and 20 K/min in non-isothermal mode. Activation energy of crystallization (Ec) has been calculated using Kissinger method, Matusita-Sakka method and Augis-Bennett method. Various kinetic parameters of crystallization kinetics like peak crystallization temperature (Tc), Rate constants (K) and order parameter (n) are determined using these DSC scans. Thermodynamic parameters such as crystallization enthalpy (ΔHc) and entropy change during the crystallization (ΔS) are also evaluated. Results are discussed using chemical bond approach.

A series of CuxMg1–xNb2O6 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) columbites were prepared using the sol-gel technique. The samples were sintered at 900 °C for 6 h. The prepared samples were structurally characterized using X-ray diffraction (XRD) method. To study their applicability in low temperature cofired ceramic (LTCC) technology, elastic properties have been characterized for mechanical compatibility. Elastic behavior was investigated at 300K, employing ultrasonic pulse-transmission technique at 1 MHz. The values of elastic moduli and acoustic Debye temperature (µD) were computed from longitudinal and shear velocities. The measured values were corrected to zero porosity using Hasselman and Fulrath's formula. The elastic constants of the samples, estimated using Modi's heterogeneous metal-mixture rule, were also reported. The variation of elastic moduli was interpreted in terms of strength of interatomic bonding. Microstructure of these samples was studied using the FESEM (field emission scanning electron microscopy) technique. Mechanical properties including yield strength, tensile strength and thermal stress resistance were calculated from thermal properties measured through thermal conductivity and thermal expansion coefficient.

We used the electrospray deposition (ESD) method to fabricate organic photovoltaic devices with poly (3-hexyl-thiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blends of different composition ratios and different organic solvent solution, namely chloroform (CLF) and dichlorobenzene (DCB). The morphology and crystallinity of the active layers were investigated by means of atomic force microscopy (AFM), two-dimensional X-ray diffraction (XRD2) and optical absorption, spreading light on the peculiarities of the present growth technique, involving much faster solvent evaporation and film forming processes, and comparatively much more ordered strutures with less need of thermal annealing processes. The power conversion efficiency (PCE) under AM 1.5G solar simulation obtained for devices deposited from DCB as compared to those deposited from CLF, showed significant improvement, in fair agreement with what was found by the overall characterization of the physical properties.