Vol 55, No 4 (2019)

We report on the application of specially-designed masks for the purpose of electrochemical etching of InP single crystals which enables one to change in a controlled fashion the direction of propagation of pores, including those propagating in directions parallel to the top surface of substrates. The fabricated templates have been used to electrochemically deposit metallic nanostructures along predefined directions and to develop two-dimensional arrays of metallic nanotubes or nanowires embedded in semiconductor matrices.

Some issues, such as leakage and tunneling currents, and light atom penetration through a thin gate dielectric, are threatening for silicon dioxide to be used as a suitable gate dielectric material for the next-generation metal-insulator-semiconductor-field-effect-transistor (MISFET) devices. A novel gate dielectric material for MISFET has been synthesized via the Pechini method by combining graphene oxide (GO)/dicalcium silicate (C₂S) components. First, GO nanoparticles were synthesized via the Hummer method and C₂S—via the Pechini method and then 0.1, 0.2, 0.4 and 0.8 the weight percentages (wt %) of GO were added into the C₂S matrix. Their nanostructural properties were studied by the field emission scanning electron microscopy X-ray diffraction, Fourier transform infrared, thermo-gravimetry and differential scanning calorimetry. The electrical properties of GO/C₂S nanocomposites, metal (Al)-GO/C₂S insulator-Si (semiconductor) were fabricated by the physical vapor deposition technique at 10^–7 Torr. The capacity, current-voltage relationship, quality factor, dissipation factor were measured with an LCR meter GPS-132A and 4-probe techniques. The frequency response of dielectric properties, dielectric constant, dielectric loss, and AC electrical conductivity, of the examined samples were studied. The electrical measurements showed that a sample with 0.4 wt % of GO nanoparticles has a higher dielectric constant at a frequency of 120 kHz (K = 62) and 1 kHz (K = 30), a lower leakage current (20 × 10^–6 A/cm²), a good carrier mobility (7.62 cm²/V s), a low threshold voltage (2.9 V), a large current I_ON/I_OFF ratio (1.25 × 10³), and a higher quality factor (32.4). Therefore, C₂S/GO nanocomposite with 0.4 wt % Go nanoparticles can be introduced as an alternative gate dielectric material for the next generation of MISFET devices.

Electrochemical deposition, structure, and properties of Fe–W alloys are studied. The alloys formed at a low current density are crystalline supersaturated solid solutions which are magnetic. At higher current densities, amorphous nonmagnetic alloys of the same composition are formed. As a result of treatment at 500–600°С, both amorphous and crystalline transform into a more equilibrium binary system, containing W solid solution in Fe and an intermetallic compound. The concentration of the remaining W in the solid solution was much higher than the equilibrium solubility. A considerable amount of hydrogen incorporates into the deposits. The deposits may be qualified as ternary Fe–W–H alloys. The incorporated hydrogen plays a crucial role in the transition from a crystalline state typical for specimens produced at low current densities to the amorphous or nanocrystalline deposits formed at higher current densities.

Using a set of glass-insulated Bi–0.02 at %Sn wires with diameters varying in a range of 0.2–1 μm prepared by liquid-phase casting by the Ulitovsky method, a complex of measurements of the temperature dependences of resistivity ρ(T), thermoelectric power α(T), and magnetic field dependences R(H) in range 4.2–300 K and Shubnikov–de Haas (SdH) oscillations in longitudinal and transverse magnetic fields up to 14 T in a temperature range of 2.1–20 K has been conducted. According to the SdH oscillation measurements, the minimum and maximum cyclotron masses, the Dingle temperature, and the position of the Fermi level ε_F in the Bi–0.02 at %Sn wires have been calculated. It has been shown that, at low temperatures, the conduction occurs only through T-holes, i.e., ε_F is located in the region of the band gap ΔE_g; it has been found that the anisotropy of the Fermi surface of the T-holes does not change after doping. The observed anomalies in the temperature dependences ρ(T), α(T), and on longitudinal magnetic field dependences R(H), which depend on wire diameter d, have been interpreted in terms of the occurrence of galvanomagnetic size effects. From the experimental data, power factor P.f. = α²σ for the Bi–0.02 at %Sn wires with different diameters in a range of 4.2–300 K has been calculated; the maximum P.f. value in different temperature ranges has been calculated. It has been found that the maximum P.f. value is achieved in a temperature range of 75–100 K, when the thermoelectric power has a positive value, which is an important factor for thermoelectric applications at low temperatures.

Different plant parts—extracts of Tribulus terrestris were employed against aluminium corrosion in basic media. The corrosion inhibition behavior of alcoholic extract of plant parts was measured by the weight loss method, the thermometric method, the potentiostatic polarization method, and electron impedance spectroscopy. The surface analysis was carried out by Fourier-transform infrared spectroscopy and scanning electron microscopy. The experiments showed an inhibition efficiency >70% with leaves extract in 0.5 M NaOH solution.

The corrosion behavior of mild steel in acid media was studied at different temperatures and over a range of concentrations of a newly synthesized azo dye, namely, 2-((E)-((Z)-(2-hydroxy- 5-((E)phenyldiazenyl) benzylidene) hydrazono) methyl)-4-(phenyldiazenyl)phenol (PBHP). Standard electrochemical methods such as potentiodynamic polarization and electrochemical impedance spectroscopy were employed for the corrosion rate measurements. As per the experimental data, the inhibition efficiency was observed to increase with an increase in the concentrations of PBHP. Potentiodynamic polarization measurements indicate that the studied inhibitor functions as mixed type and followed Langmuir adsorption isotherm. The surface morphology of the mild steel specimen was examined before and after corrosion using scanning electron microscopy and atomic force microscopy.

Tin oxide (SnO₂) nanoparticles were prepared by a low cost precipitation method. As prepared, SnO₂ nanoparticles were incorporated into polyaniline (PANI) matrix to form PANI/SnO₂ nanocomposites via liquid-liquid interfacial polymerization. The composite formation and structural changes in PANI/SnO₂ nanocomposites were investigated by X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. Electrochemical behavior of nanocomposite was evaluated in a three electrode system (in 1 M H₂SO₄) using such electrochemical techniques as cyclic voltammetry and chronopotentiometry. The calculated, via cyclic voltammetry, specific capacitance of the nanocomposite was found to be 636 Fg^–1 at a scan rate of 2 m Vs^–1. The nanocomposite exhibited a specific capacitance of 337 Fg^–1 at a current density of 0.2 Ag^–1. Further, it exhibited 73% of capacitance retention and 100% of columbic efficiency in a life cycle test conducted at 7.5 Ag^–1 for 2000 cycles.

The inhibition efficiency and adsorption of 2-[4-(dimethylamino) benzylidene] hydrazinecarbothioamide (DABHC) on the corrosion behaviour of mild steel in 0.5M H₃PO₄ and H₂SO₄ solutions has been studied in the temperature range (30–50°C) using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. The inhibition effectiveness of DABHC increases with increase in its concentration and decreases with increase in temperature. The results indicate that DABHC functions as a mixed type inhibitor and followed Langmuir’s adsorption isotherm. The corrosion inhibition of DABHC takes place through physisorption. The surface of the specimen was analysed using scanning electron microscope (SEM) and atomic force microscopy (AFM).