Thermodynamics and surface properties of liquid Al–Ga and Al–Ge alloys

The surface properties of Al–Ga and Al–Ge liquid alloys have been theoretically investigated at a temperature of 1100 K and 1220 K respectively. For the Al–Ga system, the quasi chemical model for regular alloy and a model for phase segregating alloy systems were applied, while for the Al–Ge system the quasi chemical model for regular and compound forming binary alloys were applied. In the case of Al–Ga, the models for the regular alloys and that for the phase segregating alloys produced the same value of order energy and same values of thermodynamic and surface properties, while for the Al–Ge system, the model for the regular alloy reproduced better the thermodynamic properties of the alloy. The model for the compound forming systems showed a qualitative trend with the measured values of the thermodynamic properties of the Al–Ge alloy and suggests the presence of a weak complex of the form Al₂Ge₃. The surface concentrations for the alloys show that Ga manifests some level of surface segregation in Al–Ga liquid alloy while the surface concentration of Ge in Al–Ge liquid alloy showed a near Roultian behavior below 0.8 atomic fraction of Ge.     

Electrical and optical properties of a-SexTe100–x thin films

The dc electrical conductivity of as deposited thin films of a-Se_xTe_100?x (x=3, 6, 9 and 12) is measured as a function of temperature range from 298 to 383 K. It is observed that the dc conductivity increases exponentially with the increase in temperature in this glassy system. The value of activation energy calculated from the slope of ln σ_dc vs. 1000/T plot, is found to decrease on incorporation of dopant (Se) content in the Te system. On the basis of pre-exponetial factor (σ₀), it is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The optical absorption measurements show an indirect optical band gap in this system and it decreases on increasing Se concentration. The optical constants (extinction coefficient (k) and refractive index (n)) do change significantly with the photon energy and also with the dopant Se concentration. The decrease in optical band gap may be due to the decrease in activation energy in the present system. It is also found that the real and imaginary parts of dielectric constants show a significant change with the photon energy as well as with the dopant concentration. With large absorption coefficients and compositional dependence of optical band gap and optical constants (n and k), these materials may be suitable for optical disk applications.     

Microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment

In this paper, heat treatment was carried out on Al/Al–Mg–Si alloy clad wire, and microstructure evolution and properties of Al/Al–Mg–Si alloy clad wire during heat treatment were investigated. During solution, contents of Mg and Si in inner matrix increased due to dissolution of primary Mg₂Si, and they also increased in outer matrix because Mg and Si diffused across the interface. Tensile strength of the clad wire increased firstly and then decreased, and elongation continuously increased, while conductivity continuously decreased with the increase in solution time. In aging process, Mg₂Si precipitated in both inner core and outer layer, and the content and average diameter of the precipitate increased with the increase in aging time. The content of precipitate was higher, and the average diameter was bigger in inner core. Tensile strength of the clad wire increased firstly and then decreased with the increase in aging time, and the elongation continuously decreased, while the conductivity continuously increased. The peak tensile strength of 202 MPa occurred at 8 h, when the corresponding elongation was 20 % and the conductivity reached 56.07 %IACS. Even tensile strength of the prepared clad wire approximately equaled to that of Al–0.5Mg–0.35Si alloy 203 MPa, the conductivity was obviously improved from 54.2 to 56.07 %IACS.     

Electrical switching properties of nanostructured multilayer superlattice Ge–Si…Cu…Si–Ge prepared by electron beam evaporation on glass

In this study, the fabrication of nanostructured multilayer superlattice Ge–Si…Cu…Si–Ge using electron beam evaporation on glass substrates at a temperature of 200 °C has been reported. The structural, optical and electrical characteristics of such films were then studied by means of DC polarization, powder X-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy (AFM), Rutherford backscattering (RBS) and UV–visible spectroscopic techniques. The XRD pattern obtained showed an amorphous state along with some reflected XRD signals from the Ge planes while there were no reflected signals from the Si and Cu layers. The average estimated grain size diameter (_Dav.)$\left(D_{av.}\right)$ is 30.13 nm as found from the XRD experiment using the Debye–Scherrer equation. The grain size as estimated from the AFM images was found to be within 28–31 nm, which is in good agreement with the XRD average value. RBS analysis confirmed the multilayer structure of the superlattice. The optical allowed indirect band gap of the superlattice obtained from the Tauc plot was found to be 1.19 eV, which is greater than that of bulk Ge semiconductor (0.66 eV). This fact indicates that the incorporation of a Cu layer instead of the Ge layer enables us to change the indirect to direct transitions in Ge/Si devices. Current density–voltage (J$J$–V$V$) characteristics of the nanodevice showed an electrical switching effect (VCNR) with the largest ON/OFF current ratio of the order of 10 ⁶ at 15 V.     

Electrical and thermal properties of chalcogenide glass system Se75Ge25−x Sb x

The dc and thermal conductivities of five different compositions of the chalcogenide glass system Se₇₅Ge_25–x Sb _x have been studied in a temperature range below T _g. The dc conductivity results indicate that each composition has a single activation energy in the considered temperature range. The coefficient of thermal conductivity increased linearly with temperature below T _g for the compositions investigated. The increase of Sb content in the chalcogenide glass system leads to an increased coefficient of electrical conductivity , an increased coefficient of thermal conductivity , and to a decreased activation energy E and pre-exponential factor ₀. The observed compositional dependencies of and E have been correlated with the increase of weak bond density and the decrease of covalent bond density in the structure of the compositions investigated with increasing Sb content at the expense of Ge content. The decrease in ₀ and the increase in has been, respectively, correlated with the decrease in mobility and the increase in phonon velocity.     

Electrical properties and microstructural characterization of Ni/Ta contacts to n-type 6H–SiC

A Ni/Ta bilayer is deposited on n-type 6H–Si C and then annealed at different temperatures to form an ohmic contact. The electrical properties are characterized by I–V curve measurement and the specific contact resistance is extracted by the transmission line method. The phase formation and microstructure of the Ni/Ta bilayer are studied after thermal annealing. The crystalline and microstructure properties are analyzed by using glance incident x-ray diffraction(GIXRD),Raman spectroscopy, and transmission electron microscopy. It is found that the transformation from the Schottky to the Ohmic occurs at 1050?C and the GIXRD results show a distinct phase change from Ta2 C to Ta C at this temperature. A specific contact resistance of 6.5×10-5?·cm2is obtained for sample Ni(80 nm)/Ta(20 nm)/6H–Si C after being annealed at 1050?C. The formation of the Ta C phase is regarded as the main reason for the excellent Ohmic properties of the Ni/Ta contacts to 6H–Si C. Raman and TEM data reveal that the graphite carbon is drastically consumed by the Ta element, which can improve the contact thermal stability. A schematic diagram is proposed to illustrate the microstructural changes of Ni/Ta/6H–Si C when annealed at different temperatures.     

On the properties and stability of thermally evaporated Ge–As–Se thin films

Thin films of Ge–As–Se chalcogenide glasses have been deposited by thermal evaporation from bulk material and submitted to thermal treatments. The linear refractive index and optical band-gap for as-deposited and annealed films have been analyzed as function of the deposition parameters, chemical composition and mean coordination number (MCN). The chemical composition of the films was found to be directly affected by deposition rate, with low rates producing films with elevated Ge and reduced As content, whilst at high rates the Ge content was generally reduced and As levels increased compared with the bulk starting material. As a result films with close to the same stoichiometry as the bulk glass could be obtained by choosing appropriate deposition conditions. As-deposited films with MCN in between 2.44 and 2.55 showed refractive indices and optical band-gaps very close to those of the bulk glass whereas outside this range the film indices were higher and the optical gaps lower than those of the bulk glass. Upon annealing at close to their glass transition temperature, high MCN films evolved such that their indices and band-gaps approached the bulk glass values whereas at low MCN films resulted in no changes to the film properties.     

Structural and magnetic properties of nanostructured Mn–Al–C magnetic materials

Pre-alloyed Mn_50+x−yAl_50−xC_y   (x=0$x=0$, 2, 4, 6, 8; y=0$y=0$, 1.7, 3) powders were mechanically milled (MM), and the as-milled powders subsequently annealed at temperatures from 350 to 600 °C to produce the ferromagnetic metastable L1₀-structured τ-phase. Bulk Mn₅₄Al₄₆ specimens were also annealed under the same conditions for comparison. The effects of the Mn concentration and C additions on phase formation, microstructure, magnetic properties, as well as on the magnetization mechanism of the Mn–Al–C alloys were systematically investigated. It was found that the magnetic properties are strongly dependent both on the fraction of the τ-phase and its microstructure. There exists a strong influence of the microstructural refinement, due to the ball milling, on the rate of ε-phase to τ-phase transformation and on the stability of the τ-phase. The kinetics of formation and subsequent decomposition of the magnetic τ-phase were markedly different in the MM and bulk alloys. Both remanence curves and δM plots showed no exchange coupling among the τ-phase nanograins. The mechanism for the magnetization process was determined to be domain wall pinning.     

Optoelectronic properties of Ni–GaP diodes with a modified surface

We report the promising results for Ni–GaP Schottky diode structures manufactured on the substrates with chemically-etched nano-scale surface formations that are responsible for a clearly marked luminescence band located at the energy exceeding the band gap of the bulk GaP. The other peculiarity produced by surface patterning concerns a remarkable redshift of material's optical absorption edge. At the room temperature, the height of potential barrier for Ni–GaP structure is 1.8 eV, with the monochromatic sensitivity peaking at 0.35 A/W. The comparative study of diode performance under different light sources exhibited the pronounced linear photocurrent-illumination dependence for about five orders of illumination magnitude, evidencing good optical and electrical quality of Ni–GaP diodes with surface-modified semiconductor substrate.     

Effect of SnI2 on the thermal and optical properties of Ge–Se–Te glasses

A systematic series of (Ge₂₀Se₁₅Te₆₅)_1?x–(SnI₂)_x (x = 0, 0.05, 0.1, 0.15) chalcogenide glasses have been prepared. The amorphous nature can be confirmed by XRD and SEM. With the SnI₂ content increasing, the indirect optical band gaps are decreased from 0.662 to 0.622 eV according to Tauc laws. The introduction of SnI₂ makes the glasses much easier to prepare and more stable against crystallization, making them drawable as optical fibers. The highest ΔT (130 °C) value for (Ge₂₀Se₁₅Te₆₅)_0.9–(SnI₂)_0.1 glass composition can be obtained. A slight red-shifting of the long-wavelength cutting-off edge from 18.4 to 19.4 μm was shown and it seems that SnI₂ in these glasses offers the improvement in the far-infrared properties.     

Electrical properties of a solid polymeric electrolyte of PVC–ZnO–LiClO4

The ZnO filler has been introduced into a solid polymeric electrolyte of polyvinyl chloride (PVC)–ZnO–LiClO₄, replacing costly organic filler for conductivity improvement. Ionic conductivity of PVC–ZnO–LiClO₄ as a function of ZnO concentration and temperature has been studied. The electrolyte samples were prepared by solution casting technique. The ionic conductivity was measured using impedance spectroscopy technique. It was observed that the conductivity of the electrolyte varies with ZnO concentration and temperature. The temperature dependence on the conductivity of electrolyte was modelled by Arrhenius and Vogel–Tammann–Fulcher equations, respectively. The temperature dependence on the conductivity does not fit in both models. The highest room temperature conductivity of the electrolyte of 3.7 × 10⁻⁷ Scm⁻¹ was obtained at 20% by weight of ZnO and that without ZnO filler was found to be 8.8 × 10⁻¹⁰ Scm⁻¹. The conductivity has been improved by 420 times when the ZnO filler was introduced into the PVC–LiClO₄ electrolyte system. It was also found that the glass transition temperature of the electrolyte PVC–ZnO–LiClO₄ is about the same as PVC–LiClO₄. The increase in conductivity of the electrolyte with the ZnO filler was explained in terms of its surface morphology.     

Absorption and emission properties of Bi-doped Mg–Al–Si oxide glass system

A new Bi-doped Mg–Al–silicate glass is suggested and investigated. It can be fabricated by moderate-temperature routine technology. The characteristic relaxation time of 300–800 μs in combination with the high quantum yield (up to 85%) and wide excitation spectrum makes this glass a promising laser material. The obtained quadratic dependence of the visible absorption intensity is an argument in favor of the hypothesis that the absorption and infrared luminescence in Bi-doped glasses are caused by Bi₂ dimers.     

Influence of the selenium content on thermo-mechanical and optical properties of Ge–Ga–Sb–S chalcogenide glasses

A number of Ge₁₇Ga₄Sb₁₀S_69−xSe_x (x = 0, 15, 30, 45, 60, and 69) chalcogenide glasses have been synthesized by a melt-quenching method to investigate the effect of the Se content on thermo-mechanical and optical properties of these glasses. While it was found that the glass transition temperature (T_g) decreases from 261 to 174 °C with increasing Se contents, crystallization temperature (T_c) peak only be observed in glasses with Se content of x = 45. It was evident from the measurements of structural and physical properties that changes of the glass network bring an apparent impact on the glass properties. Also, the substitution of Se for S in Ge–Ga–Sb glasses can significantly improve the thermal stability against crystallization and broaden the infrared transmission region.     

Some optical properties of Ge–S amorphous thin films

Amorphous Ge_xS_1−x films (x=0.27, 0.32, 0.36 and 0.4) were prepared by thermal evaporation. The values of the refractive index, the optical gap and the parameters of the Wemple–DiDomenico single oscillator model were determined. Using Miller's generalized rule the values of the third-order non-linear susceptibility were also estimated. Thermally induced bleaching was observed for films studied. Photobleaching was observed for sulfur rich and nearly stoichiometric films (x=0.27, 0.32) while for a germanium rich film (x=0.4) no response to the illumination was observed. The differences in photobleaching are attributed to the role of p-lone pair states and to an overall network rigidity of the films.     

Electrical properties of p-type and n-type ZnSeZnTe strained-layer

ZnSe and ZnTe semiconducting materials are highly promising candidates for the fabrication of short-wavelength light-emitting devices. We have grown ZnSeZnTe strained-layer superlattices (SLSs) on InP substrates by molecular beam epitaxy. In addition to undoped SLSs, two kinds of modulation doped SLS samples were prepared in this study, the first with Ga-doped ZnSe layers and undoped ZnTe layers, and the second with undoped ZnSe layers and Sb-doped ZnTe layers. Van der Pauw measurements of the SLS samples at room temperature showed that their electrical properties can be controlled by using the modulation doping technique. The undoped sample and the Ga-doped sample exhibited n-type conduction, whereas p-type conduction was observed for the Sb-doped sample. Interdiffusion profiles of dopants were measured by secondary ion mass spectroscopy, and significant Ga redistribution was observed. Finally, we have fabricated pn junctions from ZnSeZnTe SLSs, and measured their current-voltage characteristics.