Electronic properties of Al/DNA/p-Si MIS diode: Application as temperature sensor

The current-voltage (I-V) measurements were performed in the temperature range (200-300 K) on Al/DNA/p-Si Schottky barrier type diodes. The Schottky diode shows non-ideal I-V behaviour with ideality factors n equal to 1.34 ± 0.02 and 1.70 ± 0.02 at 300 K and 200 K, respectively, and is thought to have a metal-interface layer-semiconductor (MIS) configuration. The zero-bias barrier height Φ_b determined from the I-V measurements was 0.75 ± 0.01 eV at 300 K and decreases to 0.61 ± 0.01 eV at 200 K. The forward voltage-temperature (V_F-T) characteristics were obtained from the I-V measurements in the temperature range 200-300 K at different activation currents (I_F) in the range 20 nA-6 μA. The V_F-T characteristics were linear for three activation currents in the diode. From the V_F-T characteristics at 20 nA, 100 nA and 6 μA, the values of the temperature coefficients of the forward bias voltage (dV_F/dT) for the diode were determined as −2.30 mV K⁻¹, −2.60 mV K⁻¹ and −3.26 mV K⁻¹ with a standard error of 0.05 mV K⁻¹, respectively.     

Evaluation of metastable pitting on titanium by charge integration of current transients

The metastable pitting of titanium has been studied under potentiostatic control in solutions containing chloride ions. An approach based on the charge integration of current transients was proposed for a quantitative determination of metastable pitting. A pit density (d_mpit) was defined as the number of metastable pits per unit area per unit time (cm⁻² h⁻¹) with a typical size, instead of a size distribution. The calculated d_mpit of titanium at 0.5 V_SCE in 0.6 M NaCl was about 1.0 × 10³ cm⁻² h⁻¹ with a typical radius of 0.12 μm. An exponential potential dependence of d_mpit was obtained through the integration approach.     

Unidirectional solidification of Zn-rich Zn–Cu peritectic alloys—II. Microstructural length scales

Experimental results are presented of solidification microstructure length scales including η-phase cell spacing, primary ε secondary dendrite arm spacing, size of nonaligned dendrite of primary ε, and volume fraction of primary ε, as functions of alloy concentration (containing up to 7.37 wt% Cu) and growth velocity (ranging from 0.02 to 4.82 mm/s) in the unidirectional solidification of Zn-rich Zn–Cu peritectic alloys. Intercellular spacing (λ) of two-phase cellular structure decreases with increasing growth velocity (V) such that λV^1/2 is constant at a fixed alloy concentration in parametric agreement with the KGT and Hunt–Lu models. The value of λV^1/2 varies from 216±10 to 316±55 μm^3/2/s^1/2 with decrease in alloy concentration from 4.94 to 2.17 wt% Cu. These values are much greater than for normal eutectic systems but comparable with monotectic alloys. Dendritic secondary arm spacing (λ₂) of primary ε decreases with increasing V such that λ₂V^1/3 is constant ranging 14.9±0.9 to 75.6±8.1 μm^4/3/s^1/3 with increase in alloy concentration (C₀) from 2.17 to 7.37 wt% Cu, which is in parametric agreement with predictions of arm-coarsening theory. The volume fraction (f_ε) of primary ε increases with increasing V for Zn-rich Zn–3.37, 4.94 and 7.37 wt% Cu hyperperitectic alloys. Predictions of the Scheil and Sarreal–Abbaschian models show good agreement with the observed f_ε for Zn–4.94 wt% Cu at moderate V from 0.19 to 2.64 mm/s, but fail at low V of less than 0.16 mm/s and at high V of greater than 3.54 mm/s. The measured average size, Λ, of nonaligned dendrites of primary ε decreases with increasing V such that ΛV^1/2 is constant for a given alloy, increasing from (0.98±0.04)×10³ to (7.2±0.7)×10³ μm^3/2/s^1/2 with increase in alloy concentration from 2.17 to 4.94 wt% Cu.     

Influence of growth rate on microstructure, microhardness, and electrical resistivity of directionally solidified Al-7 wt% Ni hypo-eutectic alloy

Al-7 wt% Ni alloy was directionally solidified upwards with different growth rates, V (8.3–489.5 μm/s) at constant temperature gradient, G (4.2 K/mm) using a Bridgman-type growth apparatus. The dependence of the dendritic microstructures such as primary dendrite arm spacing (λ ₁) and secondary dendrite arm spacing (λ ₂) on the growth rate were determined using a linear regression analysis. The present experimental results were also compared with similar previous experimental results. Measurements of microhardness (HV) and electrical resistivity (ρ) of the directionally solidified samples were carried out. The dependence of the microhardness and electrical resistivity on the growth rate (V) was also analyzed. According to these results, it has been found that, for increasing values of V, the values of HV and ρ increase. However, the values of HV and ρ decrease with increasing values of λ ₁ and λ ₂.     

Electrical characterization of Au/n-GaN metal-semiconductor and Au/SiO2/n-GaN metal-insulator-semiconductor structures

In the present work, we have investigated the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Au/SiO₂/n-GaN metal-insulator-semiconductor (MIS) Schottky diode and compared with Au/n-GaN metal-semiconductor (MS) Schottky diode. Calculations showed that the Schottky barrier height and ideality factor of the MS Schottky diode is 0.79 eV (I-V), 0.87 eV (C-V) and 1.45, respectively. It is observed that the Schottky barrier height increases to 0.86 eV (I-V), 0.99 eV (C-V) and ideality factor deceases to 1.3 for MIS diode. For the MS diode, the calculated doping concentration is 4.17 × 10¹⁷ cm⁻³. However, in the case of the MIS Schottky diode, the decrease in doping concentration is observed and the respective value is 2.08 × 10¹⁷ cm⁻³. The obtained carrier concentration of the MIS diode is reduced about 50% when compared to the MS diode. The interface state density as determined by Terman's method is found to be 3.79 × 10¹² and 3.41 × 10¹⁰ cm⁻² eV⁻¹ for the MS and MIS Schottky diodes, respectively. The calculated interface densities are 2.47 × 10¹¹ cm⁻² eV⁻¹, 3.35 × 10¹¹ cm⁻² eV⁻¹ and 3.5 × 10¹¹ cm⁻² eV⁻¹ for the sweep rates of 300, 450 and 600 mV/s from MOS C-V measurements for the MIS Schottky diode. The interface state density calculated from Terman's method is found to be increased with sweep rate. From the C-V measurement, it is noted that the decrease in the carrier concentration in MIS diodes as compared to MS diode may be due to the presence of oxide interfacial layer. DLTS measurements have also been performed on MIS Schottky diode and discussed.     

CrAlYN/CrN superlattice coatings deposited by the combined high power impulse magnetron sputtering/unbalanced magnetron sputtering technique

CrAlYN/CrN coatings represent a new generation Ti-free PVD coatings tailored to serve high temperature applications such as dry high speed machining and protection of special grades aerospace and automotive alloys against environmental attack. The novel High Power Impulse Magnetron Sputtering (HIPIMS) technique was used for substrate pre-treatment (etching) followed by coating deposition utilising Unbalanced Magnetron Sputtering (UBM). The employment of HIPIMS resulted in smooth (R_a = 0.036 μm) and well adherent films with typical scratch adhesion critical load values on M2 high speed steel of L_C = 65 N. Low-angle XRD analysis showed that the coating has a nanoscale multilayer (superlattice) structure with a typical bi-layer thickness of 4 nm. XTEM observations confirmed this result and further revealed the dense, growth defect free structure of the coating due to the HIPIMS etching. CrAlYN/CrN combines high hardness of HK_0.025 = 3320 with a low coefficient of friction of 0.5 and an exceptionally low sliding wear coefficient of 3.7 × 10^− 17 m³ N^− 1 m^− 2, which is comparable to that of TiAlN/VN and Me-Carbon films. In dry high speed milling (V_cutting = 385 m min^− 1) of hardened A2 tool steel (HRC = 58), 8 mm cemented carbide ball nosed end mills coated with CrAlYN/CrN outperformed TiAlCrYN, which is one of the market leading coatings dedicated to this application. When the test is carried out at the higher end of the cutting speed range of 500 m min^− 1 this difference in performance becomes even more pronounced (factor of 8 longer life time), which demonstrates the excellent quality of CrAlYN/CrN.     

Selective single pulse femtosecond laser removal of alumina (Al2O3) from a bilayered Al2O3/TiAlN/steel coating

We studied surface modification of a double layer protective coating on steel induced by single fs laser pulse irradiation in ambient air. The outer alumina (Al₂O₃) layer, which protects against aggressive environments, was 1.7 μm thick and the titanium aluminum nitride (TiAlN) layer in contact with the steel surface had a thickness of 1.9 μm. The pulses (λ = 775 nm, τ = 200 fs) were generated by a Ti:sapphire laser source. The pulse energy was varied from 0.32 μJ to 50 μJ, corresponding to an incident laser fluence of 0.11 J cm^− 2 to 16.47 J cm^− 2. The surface damage threshold was found to be 0.20 J cm^− 2 and the alumina layer removal was initiated at 0.56 J cm^− 2. This selective ablation of alumina was possible in a wide range of fluences, up to the maximum applied, without ablating the TiAlN layer beneath.     

Synthesis of vanadium oxide, V6O13 hollow-flowers materials and their application in electrochemical supercapacitors

Hollow flowers-like V₆O₁₃ with an average size of 3 μm was successfully synthesized via a facile sol-hydrothermal approach in a short time. The surface composition, crystalline components and morphology of V₆O₁₃ were characterized by X-ray photoelectron spectra (XPS), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. An intercalating-exfoliating-self-assembly model was proposed to explain the formation process of hollow-flower structure based on experimental results. The obtained hollow flowers-like V₆O₁₃ exhibits high specific capacitance, good cyclability and low resistance as revealed by analysis of cyclic voltammetry (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). Experimental results also indicate that hollow flowers-like V₆O₁₃ can deliver a capacitance of 417 F g⁻¹ at a scan rate of 5 mV s⁻¹. This value would decrease to 400 F g⁻¹ after 1000 cycles in potential range from 0 to 0.8 V versus saturated calomel electrode (SCE) in 1 mol L⁻¹ NaNO₃ aqueous electrolyte at pH of 2.     

Magnetomechanical properties of epoxy-bonded Sm1−xNdxFe1.55 (0 ≤ x ≤ 0.56) pseudo-1-3 magnetostrictive particulate composites

Pseudo-1-3 magnetostrictive particulate composites consisting of light rare earth (Sm and Nd)-based magnetostrictive Sm_1−xNd_xFe_1.55 particles with the Nd content x of 0-0.56 and randomly distributed sizes of 10-180 μm embedded and aligned in a passive epoxy matrix are fabricated using the particulate volume fraction of 0.5. The quasistatic magnetomechanical properties of the composites are investigated and the results are compared with their monolithic alloys for various x. The composites exhibit similar qualitative trends in properties with the alloys for all x. The Sm_0.92Nd_0.08Fe_1.55 composite shows a large unsaturated magnetostriction λ of −530 ppm at 500 kA/m and a high piezomagnetic coefficient d₃₃ of −2.0 nm/A at 100 kA/m as a result of the magnetocrystalline anisotropy compensation between Sm³⁺ and Nd³⁺ ions in the Sm_0.92Nd_0.08Fe_1.55 alloy.     

Temperature dependent admittance spectroscopy of GaAs/AlGaAs single-quantum-well laser diodes (SQWLDs)

In this study, the main electrical parameters, such as doping concentration (N_D), barrier height (Φ_CV), depletion layer width (W_D), series resistance (R_s) and Fermi energy level (E_F), of GaAs/Al_xGa_1−xAs single quantum well (SQW) laser diodes were investigated using the admittance spectroscopy (C-V and G/ω-V) method in the temperature range of 80-360 K. The reverse bias C⁻² vs. V plots gives a straight line in a wide voltage region, especially in weak inversion region. The values of Φ_CV at the absolute temperature (T = 0 K) and the temperature coefficient (α) of barrier height were found as 1.22 eV and −8.65 × 10⁻⁴ eV/K, respectively. This value of α is in a close agreement with α of GaAs band gap (−5.45 × 10⁻⁴ eV/K). Experimental results show that the capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the diode are affected by not only temperature but also R_s. The capacitance-voltage-temperature (C-V-T) and conductance-voltage-temperature (G/ω-V-T) characteristics confirmed that temperature and R_s of the diode have effects on the electronic parameters in SQW laser diodes.     

Effects of Sn-substitution on the microstructure and magnetic properties of Bi-CVG ferrite with low temperature sintering

[Bi_0.75Y_1.05−xCa_1.2+x](Fe_4.4−xSn_xV_0.6)O₁₂ (Sn_x:Bi-CVG) ferrite materials were prepared by conventional ceramic technique. The bulk density, microstructure and the magnetic properties of the obtained samples were analyzed. The results showed that moderate addition of Sn⁴⁺ in Bi-CVG could lower the sintering temperature and enhance the soft magnetic properties obviously. With the increase of Sn⁴⁺ content, the saturation magnetization first increased and then decreased, while the coercivity and the ferromagnetic resonance linewidth (ΔH) first sharply decreased and then slightly increased. Additionally, the specimen of [Bi_0.75Y_0.65Ca_1.6](Fe_4.0Sn_0.4V_0.6)O₁₂ sintered at 1075 °C possessed the highest density and the optimum magnetic properties: RD (the relative density) = 98.49%, H_c = 152.3 A/m, 4πM_s = 711.3 × 10⁻⁴ T, ΔH = 2.1 kA/m.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Determining the Effects of Growth Velocity on Microstructure and Mechanical Properties of Ti-47Al Alloy using Electromagnetic Confinement and Directional Solidification

Directionally solidified Ti-47Al samples without contamination were obtained by the electromagnetic confinement and directional solidification technique. With increasing growth velocity, the solid/liquid interface was changed from cellular to dendritic. The grain boundary turned vague, and the lamellae within the grains became distorted. When the growth velocity increased to 200 μm/s, some γ phases and α phases appeared in local region owing to the enrichment of Al solute. The columnar grain size (λ), interdendritic spacing (λ ₁), and interlamellar spacing (λ _L) were measured, and the effects of growth velocity on these parameters were discussed. As the growth velocity increased, both the microhardness and the 0.2% offset compression yield stress increased continuously. However, the value of yield stress decreased slightly when the growth velocity increased to 200 μm/s, which resulted from the appearance of γ phases.     

Hydrogen embrittlement of duplex stainless steel under cathodic protection in acidic artificial sea water in the presence of sulphide ions

By slow strain rate technique, hydrogen embrittlement (HE) of a 2205 duplex stainless steel was studied in deaerated acidic (pH 6.5) artificial sea water, in the absence and in presence of sulphide ions (1-30 ppm). Strain rate tests (1 × 10⁻⁶ s⁻¹) were performed on specimens polarized at −0.9; −1.0 and −1.2 V_SCE at 25 ± 0.1 °C. HE was evaluated by R, the ratio between the % elongation to fracture in the aggressive solution and in air.Duplex stainless steel were subjected to HE in acidic artificial sea water at −0.9 V_SCE. HE increased at −1.0 V_SCE but it was reduced at −1.2 V_SCE. This decrease was attributed to the influence of a calcareous deposit.Sulphide ions at 1 ppm were sufficient to stimulate HE of duplex stainless steel. The higher the sulphide amount and the more negative the cathodic potential, the higher HE was. In the presence of S²⁻, the shielding effect of the calcareous deposit was not evident.     

Optimization of anodic layer properties on aluminium in mixed oxalic/sulphuric acid bath using statistical experimental methods

The properties of oxide layer obtained on aluminium in mixed electrolytes of oxalic acid-sulphuric acid are optimized using experimental design. For this purpose, a four variables Doehlert design (bath temperature, anodic current density, sulphuric acid and oxalic acid concentrations), was achieved. In order to maximize the growth rate and the microhardness of the anodic oxide layer and to minimize in the same time their chemical and abrasion resistances, a multicriteria optimization using desirability function was conducted. Dissolution rate of the oxide in phospho-chromic acid solution (ASTM B 680-80) was used to express its chemical resistance.Under the determined optimal anodizing conditions (C_ox = 12.6 g L^− 1, 10 °C, 2.6 A dm^− 2, C_sul = 183.6 g L^− 1), the estimated response values were 0.73 μm min^− 1, 4.38 g m^− 2 min^− 1, 481 Hv and 53.3 g m^− 2 for growth rate, dissolution rate, microhardness and weight loss after abrasion respectively. The higher abrasion and chemical resistances of the optimum anodic layer can be correlated with its morphology revealed by AFM and SEM observations.     

Pb-free glass frits prepared by spray pyrolysis as inorganic binders of Al electrodes in Si solar cells

Pb-free glass frits prepared by spray pyrolysis for Al electrodes were of fine size, spherical morphology and dense structure. Their mean size and geometric standard deviation when prepared at 1,200 °C were 1.0 μm and 1.4, respectively. Their glass transition temperature (T_g) was 374 °C. An Al electrode formed from Al paste with glass frits had a dense structure and good adhesion to the Si substrate. It had a well-developed back-surface field layer of 17.5 μm thickness. Al electrodes formed from Al paste without glass frits had sheet resistances between 21 and 32 mΩ sq⁻¹ as the firing temperature changed from 600 to 900 °C. This compared with values from electrodes formed with frits that decreased from 20 to 7 mΩ sq⁻¹ over the same range of firing temperatures.     

Temperature dependent current-voltage and capacitance-voltage characteristics of chromium Schottky contacts formed by electrodeposition technique on n-type Si

The variations in the electrical properties of Cr Schottky contacts formed by electrodeposition technique on n-type Si substrate have been investigated as a function of temperature using current-voltage (I-V) and capacitance-voltage (C-V) measurements in the temperature range of 80-320 K by steps of 20 K. The basic diode parameters such as ideality factor (n) and barrier height (Φ_b) were consequently extracted from the electrical measurements. It has been seen that the ideality factor increased and the barrier height decreased with decreasing temperature, when the I-V characteristics were analyzed on the basis of the thermionic emission (TE) theory. The abnormal temperature dependence of the Φ_b and n and is explained by invoking two sets of Gaussian distribution of barrier heights at 320-200 K, and 180-80 K. The double Gaussian distribution analysis of the temperature-dependent I-V characteristics of the Cr/n-type Si Schottky contacts gave the mean barrier heights of 0.910 and 0.693 eV and standard deviations (σ_s) of 109 mV and 72 mV, respectively. Then, these values of the mean barrier height have been confirmed with the modified ln(I₀/T²) − q²/2k²T² versus 1/T plot which belongs the two temperature regions.     

Optical properties of highly Er-doped sodium-aluminium-phosphate glasses for broadband 1.5 μm emission

Erbium-doped Na₃Al₂P₃O₁₂ (NAP) glasses with compositions 92NAP-(8−x)Al₂O₃-(x)Er₂O₃ (where x = 2-8) were prepared and characterized for absorption, visible and NIR emission and decay time properties. Judd-Ofelt analysis has been carried out to predict radiative properties of luminescent levels of Er³⁺ ions. Comparatively larger photoluminescence lifetimes (7.86 ms) and larger quantum efficiencies (74%) for the laser transition, ⁴I_13/2 → ⁴I_15/2 (at 1.54 μm) are observed. The moisture insensitivity, large Er³⁺ ion doping capability and relatively high-gain and broad emission at 1.5 μm are the most notable features of these glasses to realize efficient short-length optical amplifiers.     

Effect of sintering temperature and time on densification, microstructure and properties of the PZT/ZnO nanowhisker piezoelectric composites

Lead zirconate titanate (PZT) based piezoelectric composites embedded with ZnO nanowhiskers (ZnO_w) were investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. The samples are characterized by X-ray diffraction analysis and scanning electron microscopy. The results show that the increase of the sintering temperature and time is quite effective in improving the densification and piezoelectric properties of the PZT/ZnO_w composites. However, the relative density and piezoelectric properties deteriorate as the composites are sintered over the optimal sintering condition. Particularly, the PZT/ZnO_w composites sintered at 1150 °C for 2 h show excellent electrical properties of piezoelectric constant d₃₃ ∼ 471 pC/N, relative dielectric constant ? ∼ 3838, planar electromechanical coupling factor k_p ∼ 0.543, remnant polarization P_r ∼ 23.2 μC/cm² and coercive field E_c ∼ 9.2 kV/cm.     

High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputtering

As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr₂N and CrN coatings (up to 55 μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr₂N and CrN coating depositions, respectively, using a 3 kW average target power (16.7 W/cm² average target power density), a 50 mm substrate to target distance and an Ar/N₂ gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr₂N coatings, whereas the Cr₂N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr₂N coatings increased as the coating thickness increased to 30 μm and 20 μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr₂N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55 μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10 μm or higher. The 10-55 μm CrN coating exhibited low wear rates in the range of 3.5-5 × 10⁻⁷ mm³ N⁻¹ m⁻¹. To the contrary, the Cr₂N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹ were observed for different thicknesses.