Search results

The purpose of this paper is to synthesize Si (porous silicon (PS)) by laser‐induced etching (LIE) technique. The LIE process has the added advantage of a controlling size and optical properties without using of electrodes. The LIE process is a promising technique for fabricating many optoelectronic devices including: light‐emitting devices, detectors, sensors and large‐scale integrated circuits.

PS has been fabricated by LIE technique. Surface morphology and structural properties of nanostructures are characterized by using scanning electron microscopy and X‐ray diffraction (XRD). Photoluminescence (PL) measurement is also performed at room temperature by using He‐Cd laser (λ=325 nm) and Raman scattering has been investigated using Ar⁺ laser (λ=514 nm).

Surface morphology indicated that chemical reaction has been initiated with laser power density of 12 W/cm², resulting in irregular structure. Micro‐columns are structured on surface with laser power density of 25 W/cm². The pores structures are confined to smaller size, and the walls between the pore become extremely thin and shorter at 64 W/cm² power density and 120 min irradiation time. PL spectra at room temperature for PS prepared at power density of 64 W/cm² and irradiation time of 120 min shows the blue shift of PL at 400 nm and the full‐width and half maximum is about 60 nm. The broadening of the band gap energy occurs with a decrease of the crystallite size. The average diameter of nanosize Si crystallites is about 6‐10 nm. XRD indicated that the broadening in spectrum is due to the small size crystallites.

LIE processes have been used to produce high‐luminescent nanocrystallites with small size and size distribution, which is due to the quantum confinement effect.

The purpose of this paper is to analyse the influence of various firing profiles on microstructural and dielectric properties of low-temperature, co-fired ceramic (LTCC) substrates in a GHz frequency range. According these analyses, sintering process can be controlled and modified to achieve better performance of devices fabricated from LTCC substrates.

Samples from LTCC substrates GreenTape 951 and GreenTape 9K7 were sintered by four firing profiles. Basic firing profile recommended by the manufacturer was modified by increasing the peak temperature or the dwell time at the peak temperature. The influence of firing profile on microstructural properties was analysed according to measurements by X-ray diffractometer (application of the Cu K-alpha radiation and the Bragg-Brentano method), and the influence on dielectric properties (dielectric constant and dielectric losses) was analysed according to measurements by split cylinder resonator method at 9.7 and 12.5 GHz.

Rising of the peak temperature or extension of dwell time at this temperature has influence on all analysed properties of LTCC substrates. Size of crystallites can be changed by modification of firing profile as well as microdeformation. In addition, dielectric properties can be changed too by modification of the firing profile. Correlation between microdeformation and dielectric losses was observed.

The novelty of this work lies in finding the mutual relationship between changes in microstructural (size of grains and microdeformation) and dielectric properties (dielectric constant and dielectric losses) caused by different firing profiles.

The purpose of this study was to investigate the influence of doping ions Mg²⁺, Zn²⁺, Al³⁺ to the structure of hydroxyapatite (HAP; Ca₁₀(PO₄)₆(OH)₂) and subsequently to evaluate their adaptation in structure and their anticorrosive properties.

The substituted hydroxyapatite was synthesized by precipitation method that included the addition of Mg²+, Zn²⁺ and Al³⁺ containing precursors to partially replace Ca²⁺ ions in the hydroxyapatite structure. For precipitation synthesis, three ratios of Ca/P = 1; 1.67; 3 and two values of pH = 7 and 12 were selected. Samples 1 (Ca/P = 1; pH = 7), 2 (Ca/P = 1.67; pH = 7), 3 (Ca/P = 3; pH = 7) and 5 (Ca/P = 1.67; pH = 12) were chosen to monitor the influence of doping ions Mg²⁺, Zn²⁺ and Al³⁺ to the structure of hydroxyapatite and its anticorrosive properties.

The chosen synthesis conditions are appropriate for the formation of crystalline HAP substituted by elements Mg, Zn and Al. Only for one sample (1-Mg), two different phases (hydroxyapatite and whitlockite) were identified in the phase composition. On the basis of preliminary corrosion tests, pigments were divided into three groups pursuant to their anticorrosion effectivity: pigments with high corrosion-inhibition efficiency; pigments without anticorrosive properties; and pigments that promote corrosion processes.

In addition, no doping effect can be observed except for the sample 1-Mg, which consists of two phases (hydroxyapatite and whitlockite). Preliminary corrosion tests prove that some samples of HAP have extremely high anticorrosive effectivity as effectivity of the commercial pigments. The accelerated corrosion test showed that HAP samples have insufficient corrosion-inhibition properties for coating applications compared with the commercial pigment.

The purpose of this paper is to investigate the effects of the sintering temperature on the microstructural, morphological and electrical characteristics of Zinc oxide (ZnO)-based varistors.

This study used a conventional method to design and produce ZnO varistors by sintering ZnO powder with small amounts of various metal oxides. Furthermore, the effect of sintering temperature on varistor properties of (Bi, Co, Cr, Sb, Mn)-doped ZnO ceramics was investigated in the range of 1280–1350 °C.

The obtained results showed an E_B value of 2109.79 V/cm, a V_gb value of 0.831 V and a nonlinear coefficient (α) value of 19.91 for sample sintered at temperature of 1300 °C. In addition, the low value of tan δ at low frequency range confirmed that the grain boundaries created in 1300 °C sintering temperature were obviously good.

Based on the previous research on the ZnO-based varistors, a thorough study was carried out on these components to improve their electrical characteristics. Thus, it is necessary that those varistors have low leakage current and low value of dissipation factor to ensure their good quality. High breakdown fields and nonlinearity coefficients are also required in such kind of components. The effect of sintering temperature on the varistor properties of the new compositions (zinc, bismuth, manganese, chrome, cobalt, antimony and silicon oxides)-doped ZnO ceramics was studied in the range of 1280–1350 °C. Also, the microstructure and the phase evolution of the samples sintered at various temperatures (1280 °C, 1300 °C, 1320 °C and 1350 °C) were investigated according to X-ray diffraction and scanning electron microscope measurements.

The purpose of this study is to determine the effect of current density on the surface roughness and corrosion performance of electrodeposited Co–Ni–Fe-coated mild steel. Process variables are the key factor in controlling the electrodeposition process. It is important to study the processing parameter to optimize the mechanical and corrosion resistance performance of the coating substrate.

A low-cost electrodeposition method was used to the synthesize Co–Ni–Fe coating on the mild steel substrate. In the electrodeposition, electrochemistry concept was applied. The temperature of the process was controlled at 50 ± 5°C in an acidic environment. The influence of current density (11, 22 and 33 mA/cm²) and deposition time (15, 20 and 30 min) toward the surface roughness, hardness and corrosion rate was investigated.

The increases of time deposition and current density have improved the microhardness and corrosion resistance of Co–Ni–Fe-coated mild steel. The Co–Ni–Fe nanoparticles deposited at 30 min and current density of 33 mA/cm² experienced the smallest surface roughness value (Ra). The same sample also obtained the highest Vickers microhardness of 122.6 HV and the lowest corrosion rate. This may be due to the homogenous and complete protection coating performed on the mild steel.

The findings from the study are important for future application of Co–Ni–Fe on the mild steel parts such as fasteners, car body panels, metal chains, wire ropes, engine parts, bicycle rims, nails and screws and various outdoor uses. The improvement of corrosion resistance using optimum electrodeposition parameters is essential for these applications to prolong the life span of the parts.

A new process which pertains to fabrication of Co–Ni–Fe as a protective coating on mild steel was proposed. The Co–Ni–Fe coating can enhance the corrosion protection and thus prolong the lifespan of the mild steel parts.

Over the past decades, intense efforts have been devoted to design and synthesize efficient photocatalysts which are active under sunlight for environmental and energy applications. Titanium dioxide (TiO₂) has attracted much attention over many years for organic contaminant degradation in air or water due to its strong optical absorptivity, chemical stability and low cost. However, TiO₂ has a very low photo quantum yield which prompts the easy recombination of photogeneration electron/hole pairs. In addition, bandgap of 3.2 eV restrains application of this photocatalyst mainly to the UV range.

Vertically oriented one-dimensional TiO₂ nanostructures remarkably improve electron transport by creating a direct conduction pathway, decreasing intercrystalline contacts and stretching grown structure with the specified directionality. In this research, to enhance the visible light absorbance of TiO₂, prearranged hydrogenated titanium dioxide nanorods (H-TNRs) in the presence of H₂/N₂ gas flow are hydrothermally synthesized.

The X-ray diffraction patterns illustrated the characteristic peaks of tetragonal rutile TiO₂ and confirmed that there is no phase change after hydrogenation. Trivalent titanium ions surface defects and oxygen vacancies were considered as major reasons for redshift of absorption edge toward visible region and subsequently narrowing the bandgap to 2.27 eV. The optimized photocatalysts exhibited high visible-light-driven photocatalytic activity for degradation of methylene blue in water within 210. The synthesized H-TNRs established themselves as promising photocatalysts for organic compounds degradation in the aqueous solution.

To the best of the authors’ knowledge, this work is original and has not been published elsewhere nor is it currently under consideration for publication elsewhere.

The purpose of this paper is to investigate the effect of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on improvement of physical and electrical properties of vanadyl phthalocyanine derivative. The correlation between the physical characteristics of the active layers, comprising vanadyl 2,9,16, 23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO) and PCBM, and the electrical properties of metal/organic/metal devices have been studied. The use of soluble vanadyl phthalocyanine derivative makes it very attractive for a variety of applications due to its tunable properties and high solubility.

The sandwich type structures Al/VOPcPhO/Al and Al/VOPcPhO:PCBM/Al were fabricated by spin casting the active organic layers between the top and bottom (aluminum) electrodes. The stand-alone (VOPcPhO) and composite (VOPcPhO:PCBM) thin films were characterized by X-ray diffraction, atomic force microscopy, UV/Vis and Raman spectroscopy. The electronic properties of the metal/organic/metal devices were studied using current-voltage (I-V) characteristics in dark at room temperature.

The values of barrier height for Al/VOPcPhO/Al and Al/VOPcPhO:PCBM/Al devices were obtained from the forward bias I-V curves and were found to be 0.7 eV and 0.62 eV, respectively. The present study indicates that the device employing VOPcPhO:PCBM composite film as the active layer, with better structural and morphological characteristics, results in reduced barrier height at the metal-organic film interface as compared to the one fabricated with the stand-alone film.

It is shown that doping VOPcPhO with PCBM improves the crystallinity, morphology and junction properties.

The spin coating technique provides a simple, less expensive and effective approach for preparing thin films. The soluble VOPcPhO is conveniently dissolved in a number of organic solvents.

The physical properties of the VOPcPhO:PCBM composite thin film and the electrical properties of the composite thin-film-based metal/organic/metal devices have not been reported in the literature, as far as our knowledge is concerned.

This paper aims to determine the crystallite size and microstrain values of AgSiN thin films using potential approach called approximation method. This method can be used as a replacement for other determination methods such as Williamson-Hall (W-H) plot and Warren-Averbach analysis.

The monolayer AgSiN thin films on Ti6Al4V alloy were fabricated using magnetron sputtering technique. To evaluate the crystallite size and microstrain values, the thin films were deposited under different bias voltage (−75, −150 and −200 V). X-ray diffraction (XRD) broadening profile along with approximation method were used to determine the crystallite size and microstrain values. The reliability of the method was proved by comparing it with scanning electron microscopy graph and W-H plot method. The second parameters’ microstrain obtained was used to project the residual stress present in the thin films. Further discussion on the thin films was done by relating the residual stress with the adhesion strength and the thickness of the films.

XRD-approximation method results revealed that the crystallite size values obtained from the method were in a good agreement when it is compared with Scherer formula and W-H method. Meanwhile, the calculations for thin films corresponding residual stresses were correlated well with scratch adhesion critical loads with the lowest residual stress was noted for sample with lowest microstrain and has thickest thickness among the three samples.

The fabricated thin films were intended to be used in antibacterial applications.

Up to the knowledge from literature review, there are no reports on depositing AgSiN on Ti6Al4V alloy via magnetron sputtering to elucidate the crystallite size and microstrain properties using the approximation method.

FOR something like a century graphite was considered in much the same way as other bulk minerals, and it is only within the last twenty or thirty years that it has received close scientific scrutiny. Its suitability as a moderator in nuclear fission processes has undoubtedly helped to focus scientific, as opposed to commercial, attention on this material which has enjoyed a somewhat surprising range of industrial uses.

Porous silicon (PS) was successfully fabricated using an alternating current photo-assisted electrochemical etching (ACPEC) technique. This study aims to compare the effect of different crystal orientation of Si n(100) and n(111) on the structural and optical characteristics of the PS.

PS was fabricated using ACPEC etching with a current density of J = 10 mA/cm² and etching time of 30 min. The PS samples denoted by PS₁₀₀ and PS₁₁₁ were etched using HF-based solution under the illumination of an incandescent white light.

FESEM images showed that the porous structure of PS₁₀₀ was a uniform circular shape with higher density and porosity than PS₁₁₁. In addition, the AFM indicated that the surface roughness of porous n(100) was less than porous n(111). Raman spectra of the PS samples showed a stronger peak with FWHM of 4.211 cm⁻¹ and redshift of 1.093 cm⁻¹. High resolution X-ray diffraction revealed cubic Si phases in the PS samples with tensile strain for porous n(100) and compressive strain for porous n(111). Photoluminescence observation of porous n(100) and porous n(111) displayed significant visible emissions at 651.97 nm (Eg = 190eV) and 640.89 nm (Eg = 1.93 eV) which was because of the nano-structure size of silicon through the quantum confinement effect. The size of Si nanostructures was approximately 8 nm from a quantized state effective mass theory.

The work presented crystal orientation dependence of Si n(100) and n(111) for the formation of uniform and denser PS using new ACPEC technique for potential visible optoelectronic application. The ACPEC technique has effectively formed good structural and optical characteristics of PS.