Optical and electrical properties of amorphous Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>C<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H films

We report the optical and electrical properties of a-Si:H and a-Si_{1 − x} C _x :H (x = 0.06, 0.17, 0.25,0.32) amorphous films produced by plasma deposition at constant hydrogen content. IR absorption data are used to evaluate the density of Si-H and C-H bonds and the hydrogen concentration in the films. The activation energy for conduction and the carrier mobility in the films are determined from the temperature dependence of their electrical conductivity.     

Antireflection properties of diamond-like carbon films on Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> ∼ 0.04) single crystals

The optical properties of diamond-like carbon (DLC) films obtained by plasmachemical deposition on Cd_{1 − x} Zn _x Te (x ∼ 0.04) single crystals have been studied by ellipsometry. The ellipsometric data have been interpreted within the framework of a three-layer model of the DLC film-semiconductor crystal refractory system with transition layers between the film and substrate. It is found that DLC films exhibit antireflection properties in this refractory system in the IR spectral range. It is established that the proposed antireflection film-substrate structure is stable with respect to thermal cycling and ultrasonic treatment.     

Electronic,elastic and optical properties on the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se mixed alloys

The structural, elastic, electronic and optical properties of Zn_1−x Mg _x Se ternary mixed crystals are investigated by utilizing the first-principles plane-wave pseudopotential method within the LDA approximations. Some basic physical properties, such as lattice constant, bulk modulus, second-order elastic constants (C _ij ), Shear modulus, Young’s modulus, Poison’s ratio, Lamé constants and the electronic band structures, are calculated. We have, also, predicted the optical properties such as dielectric functions, refractive index and energy loss function of these ternary mixed crystals. Our results agree well with the available data in the literature.     

Photocatalytic activities of LaFe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> nanocrystals prepared by sol–gel auto-combustion method

Nanophotocatalysts LaFe_1−x Zn _x O₃ (x = 0, 0.05, 0.1, 0.3, 0.5) were successfully prepared by sol–gel auto-combustion method. The samples were characterized by X-ray diffraction (XRD), ultraviolet/visible absorption spectra (UV–vis), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activities of the prepared samples were investigated for the photodegradation of methylene blue (MB). The results show that the lattice constant of LaFe_1−x Zn _x O₃ nanocrystals increases due to the substitution of Zn for Fe, which leads to the lattice distortion. The absorption edges of Zn-doped LaFeO₃ display a red shift with a significant absorption between 400 and 500 nm. Doping with the Zn ions enhances the photodegradation rate of LaFeO₃ for MB. The LaFe_0.7Zn_0.3O₃ particles are spherical with mean grain size of about 20–30 nm, which exhibits the highest degradation rate of 75% under irradiation time of 150 min.     

Effect of Mg content on structure and properties of Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O:Al UV transparent conducting films

Mg _x Zn_1−x O:Al (0 ≤ x ≤ 0.6) UV transparent conducting films were deposited on quartz glass by radio frequency magnetron sputtering. Effect of Mg content on structure, optical and electrical properties of Mg _x Zn_1−x O:Al films was investigated. There is a single phase of basic wurtzite structure of ZnO in Mg _x Zn_1−x O:Al films at x ≤ 0.4, and of a basic structure of cubic structure of MgO at x ≥ 0.6. The band gap can be varied from 3.27 to 5.90 eV by controlling Mg contents. The resistivity of Mg _x Zn_1−x O:Al films increase with increasing Mg content x due to the decrease of Al-doping efficiency. The electrical conduction of Mg _x Zn_1−x O:Al films can be markedly improved by increasing the Al-doping level appropriately and annealing in argon atmosphere at over 500 °C. The maximum band gap of Mg _x Zn_1−x O:Al films with wurtzite structure was found to be 5.35 eV when Mg content x is 0.4, and the minimum resistivity of 5.4 × 10⁻⁴ Ω cm was obtained when the Al/(Zn + Mg + Al) is 0.03 and the annealing temperature is over 500 °C. The average transmittance of Mg _x Zn_1−x O:Al films was higher than 86% in the wavelength region from 300 (x ≥ 0.4) to 800 nm.     

Reflection electron-energy-loss spectroscopy of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> thin films

The values of the product of the inelastic mean free path and the differential cross section for inelastic scattering of electrons have been determined from the reflection electron-energy-loss spectra of thin films of the Fe _x Si_{1 − x} system (0 ≤ x ≤ 1). A new approach to the quantitative analysis of components in such composite media is proposed.     

Structure and electrochemical hydrogen storage properties of Pd/Mg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Pd thin films prepared by pulsed laser deposition

Three-layered Pd/Mg_1−x Al _x /Pd (x = 0, 0.13, 0.21, 0.39) thin films were prepared by means of pulsed laser deposition. In the present Al concentration range, X-ray diffraction analyses showed that the Mg_1−x Al _x layer was constituted of a single phase Mg(Al) solid solution. The Mg(Al) grains are preferentially orientated along the c-axis and their size decreased (from 18.5 to 10.5 nm) as the Al content increased. Scanning electron microscopy and atomic force microscopy observations indicated that all the films exhibited a globular surface structure. However, the surface roughness of the films decreased as the Al concentration increased. Rutherford backscattering spectroscopy revealed that the Mg–Al layer density (porosity) was strongly dependent on the Al content. Successive hydriding charge/discharge cycles were performed on the different Pd/Mg_1−x Al_x/Pd films in alkaline media. The highest discharge capacity was obtained with the Pd/Mg_0.79Al_0.21/Pd film, namely ~85 μAh cm⁻² μm⁻¹ or 320 mAh g⁻¹, which corresponds to a H/M atomic ratio of ~0.48 in the Mg–Al layer.     

Optical and photoelectric properties of monoclinic Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>As<Subscript>2</Subscript> crystals

The first data are presented on the band structure of monoclinic Zn_{1 ? x} Cd _x As₂ crystals. The fundamental absorption edge of Zn_{1 ? x} Cd _x As₂ for the E ‖ c polarization is shown to be dominated by an indirect allowed transition for absorption coefficients α^‖ < 6 cm^?1 and by a direct allowed transition for α^‖ > 6 cm^?1, both transitions involving excitonic levels. The absorption edge for E ⊥ c is due to a direct forbidden transition with the participation of excitonic levels. We have determined the band gap values for these transitions in the temperature range 80–300 K, the exciton binding energy, and the ionization energies of four deep acceptor levels produced in the band gap by structural defects.     

Optical and transport properties of Fe-doped Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se (<Emphasis Type="Italic">x</Emphasis> = 0.35)

The optical and transport properties of Fe²⁺-doped Cd _x Hg_1?x Se crystals with a midgap Fe²⁺ level have been studied. The results demonstrate that Fe²⁺ ions influence both the optical and transport properties of Cd _x Hg_1?x Se〈Fe²⁺〉. The observed optical absorption bands are due to a donor Fe²⁺ level in the band gap, with a depth E _Fe = 0.21 eV, and to band-band transitions. Thermal anneals in Hg and Se vapors have different effects on the carrier concentration and mobility in the crystals. The effect of annealing on the transport properties of the Fe²⁺-doped crystals differs from that for undoped crystals and is governed by the state of point defects.     

Recombination processes in solution-grown CdSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films

CdSe_1?x Te _x (0 ≤ x ≤ 0.4) films have been grown via precipitation from aqueous solutions, and their dark, photo-, and thermally stimulated conductivity has been investigated.     

Magnetic Behaviors of Ferromagnetic Semiconductor Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te Grown by MBE

The magnetic and structural properties of MBE-grown films of Zn_1?xCr _x Te were investigated. The magnetization versus magnetic field (M–H) measurement of Zn_1?xCr _x Te (x = 0.01–0.17) showed clear hysteresis loop at low temperatures. The ferromagnetic transition temperature (T_C) estimated from the Arrott-plot analysis increased almost linearly with the Cr composition (x) up to 275 K at x = 0.17. However, in the magnetization versus temperature (M–T) measurement, the irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) processes was observed. This is typically observed in the magnetic random system such as spin-glass or superparamagnetic phase. In the high resolution transmission microscopy (HRTEM) observations, structural defects such as stacking faults and polycrystalline-like structure were observed at high Cr compositions, whereas any apparent precipitates of different phases were not seen in all the range of Cr compositions examined. The correlation of the observed magnetic randomness with the local structural defects was discussed.     

Photoluminescence Properties of the Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Y<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O Tubes Prepared by Polycarbonate Templates

We have prepared Zn_1−x Y _x O (x=0 and 0.01) tubes to study its structural and photoluminescent properties. A pore wetting process of porous polycarbonate templates with the liquid precursor and following thermal treatment were utilized for preparing the Zn_1−x Y _x O tube structure. Using the polycarbonate template with pore size of about 2 μm diameter, the Zn_1−x Y _x O tubes were obtained. Photoluminescence (PL) spectroscopy was used to measure optical emissions from 350 to 650 nm with a He-Cd laser. The results of the PL spectra show that the Zn_1−x Y _x O tubes have evident emission peaks at the UV (about 380 nm) and visible (around 500 to 650 nm) region. The emission peak at the UV region was slightly shifted to higher wavelengths with increasing Y content. Meanwhile, the green and yellow emission peaks intensity increases as Y content increases. These results are explained by the structure tuning and oxygen deficiency with the introduction of Y.     

Properties of amorphous Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H (<Emphasis Type="Italic">x</Emphasis> = 0−1) films

Plasma deposition has been used to grow Si_1?x Ge _x :H(x= 0 ? 1) films, undoped and doped with PH₃ or B₂H₆, for p-i-n solar cells and other optoelectronic applications. The optical, electrical, and photoelectric properties of the films have been studied at constant hydrogenation and doping levels. The films deposited under appropriate conditions are amorphous, and three-layer solar cells fabricated from such films offer an efficiency of 9.5% at an illumination of 100 mW/cm². The photoresponse of the a-Si_{1 ? x} Ge _x :H films strongly depends on Ge content. The hydrogen concentration in the films was controlled by varying the gas phase composition and was determined from the IR absorption in the films.     

Synthesis and properties of columbite-structure Mg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Nb<Subscript>2</Subscript>O<Subscript>6 − <Emphasis Type="Italic">x</Emphasis></Subscript>

The formation of the columbite-structure magnesium niobate MgNb₂O₆ is a multistep process. Single-phase material can only be obtained through long-term high-temperature heat treatment. Deviations from stoichiometry have a significant effect on the microwave quality factor Q of the material: magnesium-deficient ceramics contain small amounts of Nb₂O₅ and have relatively low Q values, whereas an excess of magnesium leads to the formation of Mg₄Nb₂O₉ (alpha-alumina structure) as an impurity phase, thereby drastically increasing the electrical Q.     

Dominancy of antiferromagnetism in Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O diluted magnetic semiconductors

The outline of magnetic interactions in DMSs was determined using Zn_1−x Co _x O particles, where “x” was changed as 0.01, 0.05, 0.10, 0.15, and 0.20. The syntheses were accomplished though mechanical milling and thermal treatment, known as solid state reaction. The formation of each synthesis was monitored by differential thermal and thermo gravimetric methods (DT-TGA). Substitution of Co²⁺ ions with Zn²⁺ host atoms in a ZnO lattice was analyzed using X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectroscopy, energy dispersive X-ray spectrometry (EDS) data, transmission electron microscopy (TEM) figures, scanning area electron diffraction (SAED) patterns, and X-ray photo spectroscopy (XPS) spectrum. The measured Co contents in ZnO lattice were found to be ~0.7% less than the expected result. In addition to Zn_1−x Co _x O particles, tungsten (W) contaminations were noticed in the variations of 1.5 ± 0.2%, as originating from the abrasion between the miller and balls. The progressive replacement of Co²⁺ with Zn²⁺ host ions in ZnO lattice from 1% to 20% decreased the band edge from 3.03 ± 0.01 eV to 2.95 ± 0.01 eV, respectively. Co doping has also changed the magnetic nature of the ZnO. Although having both interactions (ferromagnetic and antiferromagnetic), dominance of ferromagnetic behavior was only observed for Zn_0.99Co_0.01O with the coercivity of ~154 ± 50 Oe and positive Curie–Weiss temperature as 79 ± 1 K. However, the calculated \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values have proved that the higher Co²⁺ concentrations in ZnO lattice have increased the efficiency of antiferromagnetic interactions. Surprisingly, there was no rapid change at \frac2J_\textex k_\textB {\frac{{2J_{\text{ex}} }}{{k_{\text{B}} }}} values as mentioned in previous works.     

Microstructure and microwave dielectric properties of (Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>SiO<Subscript>4</Subscript> ceramics

(ZnMg)₂SiO₄ powders was prepared by the sol-gel process, and the microstructure and dielectric properties of (Zn_1−xMg_x)₂SiO₄ microwave materials were investigated systematically. TG-DSC and XRD analyzes for gels indicate that the (ZnMg)₂SiO₄ with pure willemite phase could be obtained at low temperature of 850°C. Further, XRD illustrates that just small amounts of Mg can be incorporated into Zn₂SiO₄ lattice, and the solid solution limit of Mg in Zn₂SiO₄ is about x = 0·1. By appropriate Mg substitution for Zn, the sintering range is widened and the sintering temperature of Zn₂SiO₄ ceramics can be lowered effectively. SEM shows that Mg-substitution for Zn can promote the grain growth of Zn₂SiO₄. Moreover, the microwave dielectric properties strongly depended on the substitution content of Mg and sintering temperatures. (Zn_0·8Mg_0·2)₂SiO₄ dielectrics sintered at 1170°C show the condense microstructure with small uniform grains and best microwave properties: ɛ _r = 6·3, Q × f = 189800 GHz and τ _f = −63 ppm/°C.     

Cd(S<Subscript>(1 − <Emphasis Type="Italic">x</Emphasis>)</Subscript> + CO<Subscript>3(<Emphasis Type="Italic">x</Emphasis>)</Subscript>) thin films by chemical synthesis

A microcrystalline mixture of cadmium carbonate (CdCO₃) and cadmium sulfide (CdS) were grown in the thin film format onto glass substrates by means of chemical bath. The temperature of the bath (T_d) was selected in the interval 23–80^∘C. At low temperatures, CdCO₃ is the compound predominant in the layers. At high temperatures CdS is the compound deposited on the substrate. At intermediate T_d-values a mixture of both materials are present, i.e., the gradual transition from an insulator (CdCO₃) to a semiconductor (CdS) growth occurs when T_d increases. Physical properties of films were studied by means of X-ray diffraction and optical absorption. The forbidden energy band gap of direct electronic transitions (E_g) was calculated by applying the α² ∝ (hν − E_g) relation to the optical absorption spectra.     

Raman spectroscopy determination of carrier concentration in <Emphasis Type="Italic">n</Emphasis>-In<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>As epitaxial films

We have studied in detail the coupled phonon-plasmon mode Raman spectra of n-In _x Ga_{1 − x} As with n in the range 10¹⁷ to 10¹⁹ cm⁻³. The results indicate that the behavior of the high-frequency mode L ₊ can be described in terms of coupled modes in the Drude approximation. The proposed theory and experimental data are used to estimate the carrier concentration in the solid solution and its composition.     

Structural and magnetic properties of Cr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> = 0−0.4) solid solutions

Cr_1?x V _x Te solid solutions with a hexagonal structure (NiAs type) have been obtained in the composition range x = 0?0.4 by direct melting of elemental mixtures, followed by annealing and quenching. The 80-K magnetic moment is found to decrease from 2.4μ_B in CrTe to 1.52μ_B in Cr_0.6V_0.4Te. The Curie temperature varies from 342 K to 321 K, respectively.     

Thermoelectric properties of perovskite oxides La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CoO<Subscript>3</Subscript> prepared by polymerlized complex method

P-type perovskite oxides La_1−x Sr _x CoO₃ (0 ≤ x ≤ 0.2) have been prepared using a polymerlized complex method and sintering. The Seebeck coefficient, electrical conductivity, and thermal conductivity of the oxides were studied from room temperature to 773 K. The ln(σT)−1/T relationships revealed small-polaron hopping mechanism for the higher Sr contents. Large Seebeck coefficients were observed in lightly Sr-doped samples. Sr doping greatly reduced the Seebeck coefficient and enhanced the electrical and thermal conductivity of the samples. The temperature-induced spin-state transition of Co³⁺ ions strongly influenced the transport properties. The highest ZT value found in this series of oxides was 0.046 at 300 K for x = 0.1.