ISSN: 0128-7389, eISSN: 0127-9645 Solid State Science and Technology is a peer reviewed journal published by the Malaysian Solid State Science and Technology Society (MASS). It was first established in 1993 and is published on a biannual basis. The journal releases two issues each year, scheduled for publication in June and December. Solid State Science and Technology provides a forum of communication for solid state scientists, material scientists, technologists and engineers and promotes the advancement and dissemination of knowledge related to the science and technology of solid state. In addition to conventional solid-state materials, Solid State Science and Technology strongly encourages and welcomes high-quality research on the exploration and application of local and indigenous materials for advanced technological applications. Such efforts contribute to the diversification of electronic and functional material sources, foster sustainable and cost-effective material development, and promote innovation rooted in regional resources with global technological relevance. The journal will consider original research papers and review articles from the national and international communities. The scope of this journal is as follows: Advanced Material Synthesis and Crystal Growth Technology Carbon and Related Materials Ceramics and Glasses Devices and Materials for Biology and Medicine Electrochemical and Solid State Lasers and Optoelectronics Materials and Energy Metals and Alloys Nanoscience and Nanotechnology Optical and Dielectric Materials Photonic Devices and Optoelectronic Integration Polymers and Composites Semiconductors and Devices Solid State Theory, Simulation and Computation Superconductors Thin Films and Nanostructures Organic Materials and Application Functional local, and indigenous resource materials
The Malaysian Solid State Science and Technology Society (MASS)
EFFECT OF ULTRASONIC IRRADIATION TIME AND AMPLITUDE VARIATION ON TiO2 PARTICLES
A novel sonochemical method has been applied to directly prepare TiO2 colloid. TiO2 colloids were synthesized by using titanium tetraisopropoxide as a precursor of titanium. Ultrasonic irradiation was applied during the reaction process of the reactants. Several variable parameters of ultrasonic irradiation were applied upon the TiO2 colloid (ultrasonic irradiation time and amplitude).Then, TiO2 colloids were used to fabricate TiO2 thin film via dip coating process. The TiO2 thin films were then calcined at 500 °C for 2 hours. The physical and chemical properties of TiO2 thin film were studied using different techniques of characterization such as X-ray diffraction (XRD), Transmission Electron Microscope (TEM), and UV-Vis spectrophotometer. It seems that increasing ultrasonic irradiation amplitude leads to the formation of bigger TiO2 particles in the colloid as confirmed by the shift of absorption edge towards shorter wavelength and TEM pictures. The efficiency of TiO2 thin film photocatalyst was evaluated on degradation of methylene blue.
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VIBRATIONAL STUDIES OF STRONTIUM ANTIMONY PHOSPHATE GLASS
Glass samples in a series of 60P2O5-xSb2O3-(40-x)SrO (95-x)P2O5-5Sb2O3-xSrO and (95-x)P2O5-xSb2O3-5SrO with 5≤x≤35 mol% were prepared using melt-quenching technique. The effect of SrO and Sb2O3 content on the structure of ternary Sb2O3-SrO P2O5 ultraphosphate glass has been measured by means of X-ray Diffraction (XRD), Infrared and Raman Spectroscopy. The results from XRD patterns indicate that the compositions containing up to 35% of Sb2O3 and/or SrO formed as a glass easily and there were no crystalline phases detected. Spectra from IR and Raman Spectroscopy indicate shows the phosphate network of these glasses was composed of branching (Q3), middle phosphate tetrahedral (Q2), pyrophosphate (Q1), and other strontium/antimony anions. The occurrences of Q1 in the crystalline ultraphosphate are due to the disproportionate of the type 2Q2 ßàQ1+Q3 that occurred in these glasses. All the symmetric and asymmetric stretching vibrations of POP and PO2 observed in the spectra are the characterization of Q3 and Q2 groups. Furthermore, the glass network, especially the Q2 unit can be modified by the SrO and Sb2O3 ions. This modification was primarily associated with the phosphate and the Q2 and Q3 units that were randomly distributed in the network. Spectroscopic results show that the modification of the phosphate network was higher and more flexible for the glass containing Sb2O3 with respect to the SrO. Formations of P-O-H bonds express the hygroscopic nature of the phosphate glass. From this study, it shows that the vibration spectroscopy (Infrared and Raman) are useful complement information about the network structure of the ultraphosphate glasses.
STUDY OF NANO-SiC ADDED MgB2 SYNTHESIZED BY USING HIGHER BORIDE PHASE AS A PRECURSOR
Both pure and nano-SiC added MgB2 were prepared by reaction of higher boride phase (MgB4) and Mg in a two-step sintering method. The first step involved a high temperature (1050 °C) synthesis of MgB4. However, this reaction gave rise to significant amount of MgO. Hence, acid treatment was done in order to remove MgO while retaining MgB4 as dominant phase. The second step was followed by the introduction of an appropriate amount of Mg into the acid washed MgB4 powders to form MgB2 at a lower sintering temperature (750 °C). Nano-SiC was added according to 2 wt%, 5 wt% and 10 wt% respectively. Both pure and added samples show MgB2 as a dominant phase. The added samples show other minor phases of Mg2Si, MgO, MgB4 and some unreacted SiC was also found. The Scanning Electron Micrographs revealed the well defined hexagonal shape of MgB2 grains and the microstructure is denser with reduced porosity as compared to the in-situ reaction of (Mg + B) samples. The density was found to increase upon increasing the SiC addition level. The superconducting properties were studied and reported as well. The MgB2 added with 2 wt% SiC has the highest transition temperature of 37K while MgB2 with 5 wt% SiC exhibits the highest Jc value at 5K at the applied field of 5T among all the added samples.
SYNTHESIS AND CHARACTERIZATION OF ZINC OXIDE NANOPARTICLES
Zinc oxide (ZnO) nanoparticles had been successfully synthesized via solution combustion method. Zinc nitrate hexahydrate (Zn(NO3)2•6H2O) and glycine (NH2CH2COOH) was used as an oxidant and fuel, respectively. These reactants were mixed in different fuel-to-oxidant (F/O) ratios before undergoes different calcination temperatures (400, 500 and 600 ºC) for 2 hours in order to obtain desired product. The synthesized ZnO powders were characterized via XRD, FT-IR, SEM and TEM. The XRD and FT-IR data confirmed the formation of high purity of ZnO nanoparticles. SEM showed the morphology of ZnO was in spherical shape. The particle size of ZnO was found to increase from low F/O to high F/O ratio. Increment in calcination temperatures also tends to form the larger particle size due to the agglomeration of the particles. ZnO nanoparticles with different sizes were prepared by adjusting the molar ratio of zinc precursor to glycine and calcination temperatures.
PHYSICAL PROPERTIES OF BOROTELLURITE GLASS DOPED WITH MANGANESE
Systematic series of borotellurite glasses doped with manganese (100-x) [(B2O3)30(TeO2)70] - xMnO with x = 0.1, 0.2, 0.3 and 0.4 were successfully synthesized by using the melt quenching technique. In this study, the remelting effect of the glass samples on their microstructure were investigated through the density measurement and FT-IR spectra, as well as being evaluated with the XRD techniques. Initial experimental results from XRD measurement show that there were two separate phases probably due to the existing of peak before the sample was remelted. The different physical behaviors of the studied glasses were closely related with the concentration of manganese in each phase. The transition temperatures of these types of glasses were found to decrease with addition of the manganese content and most probably due to the increasing of non bridging oxygen (NBO) in the borotellurite network.
DIELECTRIC PROPERTIES OF BARIUM STRONTIUM TITANATE CERAMICS AT 20 Hz TO 1 MHz
Perovskite-based ferroelectrics of Barium Strontium Titanate (BST; x=0.3-0.7) have been prepared using conventional solid-state method. The XRD showed that BST ceramics were perovskite structure without occurring secondary phase after sintered at 1200°C. However, sample x=0.3 was tetragonal phase while x=0.4-0.7 were cubic phase due to the ease of tetragonal-cubic phase transition as the strontium content increased. BST were frequency and temperature dependent. However, dielectric constant of Ba0.6Sr0.4TiO3 decreased with increasing of measuring temperature. This was due to the occurrence of impurities which diffused the dielectric constant. Beside this, non-homogeneous distribution of Ba2+ and Sr2+ would also produce the diffused phase transition response. Ba0.5Sr0.5TiO3 had the highest dielectric constant.
PHYSICAL AND STRUCTURAL PROPERTIES OF Nd2O3 DOPED BORATE GLASS
The Nd3+ doped borate glass system with composition xNd2O3-5MgO-20ZnO-(75-x) B2O3 with x = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 successfully been prepared by melt-quenched technique. The physical properties by mean of density and molar volume are well determined. From the results, the glass densities are found to increase from 3193 kgm-3 to 3530 kgm-3. The increment in density implies that an addition of Nd2O3 with higher atomic masses than B2O3 tend to increase the packing density of the glass structures since the atomic masses of B2O3 and Nd2O3 are 69.62 and 336.42 respectively. From the density values obtained, the molar volume of glasses was calculated. It is found that the molar volume of these glasses decreases slightly from 22.50 cm3 to 22.24 cm3 with respect to Nd2O3 content. Meanwhile, the structural properties have been determined by using Fourier transform infrared (FTIR) spectroscopic techniques. From the experiment, it is observed that there are several significant peaks which correspond to the structural bonding of the glass in a range of 650 – 4000 cm-1. The peaks found are consistent with the stretching and bending vibration of the glass structure as predicted.
EFFECT OF SURFACE FINISH ON INTERMETALLIC COMPOUND FORMATION DURING SOLDERING WITH Ni-DOPED SOLDERS
Solder joint reliability is dependent on both thickness and morphology of the intermetallics that form and grow at the solder joint interface during soldering and subsequent thermal ageing and examining the morphology of these intermetallics is of great importance. The focus of this paper is to present experimental results of a comprehensive study of the interfacial reactions during soldering of Sn-Ag-Cu-Ni lead free solders on copper (Cu), immersion silver (ImAg), and electroless nickel/ immersion gold (ENIG) surface finishes. Using scanning electron microscopy detailed a study of the 3-D morphology and grain size of the intermetallics was conducted. The results showed that when soldering on ENIG surface finish, several morphologies of intermetallics with different grain sizes form at the solder joint interface compared to a single intermetallic morphology that forms when soldering on copper and immersion silver. An attempt was made to discuss the effect of several factors that may have an influence on the type of morphology the intermetallics may grow into. The results obtained in the present investigation also revealed that the technique of removing the solder by deep etching to examine the morphology of intermetallics is a convenient and efficient method to investigate the intermetallics formed at the solder joints.
UV-VIS CHARACTERIZATION OF DIAMOND-LIKE CARBON THIN FILMS DEPOSITED USING (DC-PECVD)
Optical properties of Diamond-like Carbon Thin Films deposited by DC-PECVD are reported. The films were deposited on the corning glasses with the ratio of Hydrogen, H2 (97%) and Methane, CH4 (3%) and grew diamond like carbon (DLC) thin films with different temperatures up to 873K. The other important variables were fixed such as DC voltage (1.5 kV) and pressure (1 x 10-1 torr). From the light transmission using UV-Vis spectroscopy it was found that the type of optical transition is allowed indirect transition in the range of 3.8eV to 4.3eV. The thickness decreases with the increases of substrate deposition temperature. The photoluminescence analysis was order to obtain the peak of excitation and emission range of the sample films. It has been found that the transition energy in the range of 3.06 to 3.22 eV.
WARM FORMING OF IRON POWDER WITH AND WITHOUT ADMIXED LUBRICANT
This paper reports the outcomes of a comparative study between warm forming of metal powder with and without using admixed lubricant. A lab-scale warm forming rig was designed and fabricated which enabled the generation of green compacts at elevated temperature. The feedstock from iron powder ASC 100.29 was prepared by mechanically mixing the powder with 0.4 wt% and 0.8 wt% of zinc stearate for 10, 30, and 60 minutes in the case of warm forming with lubricant. For the case of forming without lubricant, only iron powder ASC 100.29 was used as feedstock. The prepared feedstock was formed by varying the temperature from 30ºC to 200ºC to generate green compacts for the purpose of mechanical testing and microstructure evaluation. The results revealed that the properties of green compacts are affected by the existence of admixed lubricant as well as forming temperature. Green compacts having high strength and more homogenous grain distributions were obtained by using admixed lubricant.
DIELECTRIC PROPERTIES OF B2O3 – TeO2 – Sm2O3 GLASSES SYSTEM
Glasses in the system containing [B2O3]0.3 [Te02]0.7-x [Sm2O3]x was prepared from melt quenching technique over a wide range of composition (x = 0.3~1.2 mol%) denoted as BTS1, BTS2, BTS3, BTS4 and BTS5 respectively. The structural changes were studied by XRD spectra, FTIR spectroscopy and DTA spectra. Network units existed in Sm3+ doped glass and Sm3+ existed as network modifier. The higher concentration of Sm3+, the more units of TeO3 would transform to TeO4. The optimum Sm3+ concentration was about 1.0 mol% (BTS4) for this glasses system. The density (ρ) and molar volume (Vm) was obtained attributed to non-bridging oxygen (NBO). The addition of samarium oxide (4f5) indicates of strong bonding between the components and enhances the glass formation ability. The dielectric properties (dielectric constant, ε’, and dielectric loss factor, ε’’), which were characterized in the frequency range 10-2 – 106 Hz over temperature range 100 – 220 oC, show a larger value at lower frequencies (below 100 Hz) and higher temperatures (above 140 oC). The graphs were fitted using Cole-Cole and Quasi dc models. Activation energy obtained from the master plot graph was found to decrease as Sm2O3 content increased. The optical band gap was found to decrease with increasing Sm2O3 content attributed to increase in degree of disorder in the system, direct consequence of the increases of NBO in the system.
GROWTH OF BINARY, TERNARY AND QUATENARY III-V COMPOUNDS NANOWORES BY MOCVD
Various III-V compounds semiconductor Nanowires (NWs) have been grown by using vertical camber MOCVD. The morphology of the NWs has been characterized using FESEM and SEM. In addition to binary and ternary NWs such as GaAs, InP, InxGa1-xAs and AlyGa1-yAs NWs, the quaternary compounds InGaAsP NWs have been successfully grown. The growth of NWs has been assisted by gold nanocolloids as seed particles. Besides this technique, seed free-assisted growth of NWs has also been demonstrated. InxGa1-xAs NWs have been successfully grown without gold seed particle assisted.
EFFECT OF SINTERING TEMPERATURE ON THE MICROSTRUCTURE AND MICROWAVE DIELECTRIC PROPERTIES OF STRONTIUM TITANATE (SrTiO3) CERAMICS
In this study, microstructure and microwave dielectric properties of strontium titanate (SrTiO3) ceramics prepared via conventional solid state reaction route were investigated. The starting materials used for the preparation of SrTiO3 were strontium carbonate (SrCO3) and titanium oxide (TiO2). SrTiO3 ceramics were calcined at 1100 °C and sintered at 1200 °C, 1300 °C, and 1400 °C respectively. Identification of crystalline compounds of SrTiO3 ceramics were analyzed using X-ray Diffraction (XRD). Microstructure of SrTiO3 ceramics were then characterized by Field Emission Scanning Electron Microscope (FE-SEM). The microwave dielectric properties of SrTiO3 were measured in the frequencies range from 1 MHz to 1.5 GHz using Agilent RF Impedance/Material Analyzer 4192B. From the XRD patterns of SrTiO3 ceramics, it showed that SrTiO3 ceramics were in crystalline structure after sintering. SrTiO3 ceramic sintered at 1400 °C has larger grain size with lower porosity. Loose and porous structure was observed for SrTiO3 ceramic sintered at 1200 °C. For SrTiO3 ceramic sintered at 1400 °C, it was observed that the dielectric constant was the highest. Lower dielectric constant was observed for SrTiO3 ceramic sintered at 1300 °C.
INFLUENCE OF SINTERING TEMPERATURE ON THE DIELECTRIC PROPERTIES OF YTTRIUM IRON GARNET (YIG)
Yttrium Iron Garnet (YIG) is widely used in microwave applications. In this study, the samples were synthesized at three different sintering temperatures which were 1300 °C, 1350 °C, and 1400 °C by conventional solid-state method. The samples were characterized by XRD and SEM to determine the crystalline structure and microstructure of the samples. The dielectric properties of the sample were measured using Novocontrol High Resolution Dielectric Analyzer in the frequency range 10 mHz to 1 MHz at different temperatures. YIG sample sintered at 1400 °C produced better grain growth of crystalline structure with higher dielectric constant and dielectric loss. The dielectric measurement revealed that the dielectric constant decreases with increasing frequency for all samples.
STRUCTURE AND MICROSTRUCTURE STUDY ON LaMnO3 AND La0.67Ba0.33MnO3: COMPARISON BETWEEN BULK AND THIN FILMS
Bulk LaMnO3 and La0.67Ba0.33MnO3 polycrystalline manganite were prepared via solid state reaction and converted into thin films via pulsed laser deposition technique. Comparison between bulk and thin films on structure and microstructure were studied. Crystal structure transformation was observed when bulk LaMnO3 converted into thin film. Clear grains was observed in bulk LaMnO3 while LaMnO3 thin film shows melted-like grains accompanied by island growth mode. Positive misfit was observed in La0.67Ba0.33MnO3 thin films due to strains induced by the lattice misfit between the deposited film and substrate. Nano-sized cracks were observed due to dissimilarity in coefficient of thermal expansion between thin film and substrate. In both LaMnO3 and La0.67Ba0.33MnO3 systems, larger lattice strain was observed in thin film sample compared to bulk. Thus, enhanced the density of system by invoke MnO6 octahedral to stretch its Mn-O-Mn bond angle and Mn-O bond length. Denser crystal system was observed in thin film sample compared to bulk.
INFLUENCE OF Ca DOPING ON THE SUPERCONDUCTIVITY OF Y1-xCaxBa2Cu3O7-δ
Here, we report the effect of Ca doping on the superconducting transition temperature (Tc), crystal structure and microstructural properties of Y1-xCaxBa2Cu3O7-δ (0 ≤ x ≤ 0.05). It was found that the variation of c-axis lattice parameter remains almost constant. However, a slight decrease in both a and b axes are noticeable leading to the reduction of orthorhombicity of Y-123 phase. The superconducting transition temperature decreases with Ca2+ substitution at the Y3+. The Tc of YBa2Cu3O7-δ (Y-123) was reduced from 91 K for x = 0.00 to 84 K for x = 0.05. The degradation of Tc is attributed to the decrease in oxygen content in the CuO chains. The superconducting transition breadth, ΔT, increases with Ca substitution indicating the degradation of crystallinity or the presence of inhomogeneity. Changes in grain size and grain boundary were also observed by SEM. As the concentration of Ca increases, the grain size becomes larger giving rise to the reduction of porosity in the system.
MECHANICAL PROPERTIES OF NIOBIUM OXIDE DOPED Y-TZP FOR BIOMEDICAL APPLICATIONS
The influence of small additions of Nb2O5 (up to 1 wt%) on the sintering behaviour of yttria-stabilized zirconia sintered over the temperature range from 1200 ºC to 1500 ºC was investigated. It was found that the mechanical properties of Yttria-tetragonal Zirconia Polycrystals ceramic (Y-TZP) were dependent on the dopant amount and sintering temperature. Fracture toughness increased as the Nb2O5 content increased, which indicated that the annihilation of oxygen vacancies in 3Y-TZP was responsible for the instability of the t-ZrO2 lattice. The results also revealed that there was no significant influence of the Nb2O5 doping on the sintered density of the Y-TZP. The relation between the measured mechanical properties is discussed with the emphasis on the role of the niobium oxide.
SYNTHESIS AND CHARACTERIZATION OF Bi3Mg2Nb3O14 PYROCHLORE SYSTEM
Synthesis of Bi3Mg2Nb3O14 pyrochlore was carried out using conventional solid-state method. Phase formation and electrical properties of Bi3Mg2Nb3O14 pyrochlore was investigated by employment of different spectroscopy techniques. The phase purity and formation mechanism were confirmed by X-ray diffraction analysis. The “ideal” Bi3Mg2Nb3O14 was formed at 1025 °C as cubic pyrochlore with minute traces of Mg4Nb2O9 and MgNb2O6 phases. The determined grain size by SEM analysis was found in the range of 1.5 - 6.5 µm. Impedance spectroscopy study revealed that Bi3Mg2Nb3O14 pyrochlore was highly resistive with high activation energy of 1.36 eV. The recorded dielectric constant, ε’, was ~110; dielectric loss, tan δ, 10-3, both at room temperature and at frequency 1 MHz. No sign of ionic conduction was discerned and the mechanism was probably attributed to hopping-type.
SINTERING EFFECT ON THE SUPERCONDUCTING PROPERTIES OF NANO-SiC ADDED MgB2
In this work, MgB2 samples added with different weight percentages (wt%) of nano-SiC additions were synthesized by the conventional solid state method. They were sintered at 650 ºC and 850 ºC respectively, in order to study the effect of sintering temperature on their phase formation and superconducting properties. XRD spectra show relatively higher intensity of Mg2Si at lower sintering temperature while Rietveld Refinement shows severe lattice contraction at a-axis but the c-axis remains unchanged with increasing SiC additions and sintering temperatures. The transition temperature degrades with the additions level but higher sintering temperature led to more gradual decrease in Tc. At 5K, samples sintered at lower temperature shows enhanced flux pinning properties with higher Jc. However, at 20K, samples sintered at higher temperature showed improved Jc at high field (>3T) when the addition level exceeds 5 wt%.
DIELECTRIC BEHAVIOR OF Ni0.1Zn0.9Fe2O4-POLYPROPYLENE COMPOSITES AT LOW MICROWAVE FREQUENCIES
In the last decade, studies and research toward polymer-clay composites draw significant attention for a suitable filler that can improve mechanical, thermal, electrical, optical and pharmaceutical properties as compared with pure polymer. Ni0.1Zn0.9Fe2O4 (NZF) was prepared using conventional solid-state method. A two phase composite was fabricated with blend filled Ni0.1Zn0.9Fe2O4 added to isotactic polypropylene matrix. The samples were characterized by XRD and dielectric measurements were done using Agilent 4291B Impedance/Material Analyzer. It was observed that the composition of 30 wt% NZF gave the highest dielectric constant in the frequency range of 1 MHz to 1.8 GHz at room temperature.
THE DEVICE PERFORMANCE DUE TO VARIATION OF PVK CONCENTRATION ACTED AS THE HOLE TRANSPORT LAYER THROUGH BLUE ORGANIC LIGHT EMITTING DIODE BY USING EMISSIVE LAYER DPVBI.
Bi-layer devices of the structure ITO/PVK/DPVBi/Al with the thickness of 4,4’bis(2, 2’-diphenyl vinyl)-1,1’ biphenyl (DPVBi) 56 nm were fabricated. In this study the performance of the device has been observed through variation in the Poly(9 vinylcarbazole) (PVK) concentration as the hole transport layer (HTL). The relation between PVK concentration and the threshold voltage, maximum voltage, and maximum current as well as luminance has been identified. The device performance was analyzed in the perspective of current voltage curved (I-V) and light intensity characteristic. From the result, the device with PVK concentration 0.7% showed the optimum performance at the threshold voltage 13.0 V and the maximum current achieved was 12.7 mV. The device is found to emit blue light spectrum centred at peak 371.92 nm with the maximum voltage 14 V, whereas the maximum luminous intensity with optimum luminance are 1.04×106 candela and 0.212 cd/m2. DPVBi acted as the emissive EL layer was embedded by thermal evaporation while PVK film was prepared by spin coated technique.
THICKNESS OPTIMIZATION OF EFFICIENT GaInNAs / GaAs SINGLE QUANTUM WELL LASERS
The effect of the single quantum well thickness on the optical and electrical parameters of a GaInNAs/GaAs quantum-well lasers are presented. It was found that the material gain spectrum is red-shifted along with increment of the FWHM as the well-layer thickness is increased. Moreover, it has been observed that the photoluminescence spectrum intensity for various thicknesses of well-layer declines as the well-layer thickness increases. The mode spectrum for different well-layer thickness is presented. The threshold current density and slope efficiency are measured and found to be decreased with the thickness increment of the well-layer.
SILICON NANODOTS GROWN ON SAPPHIRE SUBSTRATE BY A SELF ASSEMBLY GROWTH METHOD
Silicon quantum dots have been grown on sapphire substrate using a self-assembly method of physical vapour deposition. The samples were fabricated at low sputtering rate and varying experimental conditions. Apparently, the onset of nucleation took place during the first 5 minutes of deposition, followed by a further growth of stable islands so-called nanodots, with the measured radii comparable to the predicted values. Other measurement results confirmed the existence of these dots, including the bandgap energy ∼ 1.80 eV from PL and a 5% at. silicon from EDX. The nucleation parameters were predicted as follows: Free energy change per unit volume ΔGv ∼ -2.4x105 Jmol-1; Surface energies per unit area, γLN = 1.48 Jm-2, γNS = 21.6 - 88.3 Jcm-2 and γLS = 0.82 x 10-2 Jm-2; Critical energies ΔG* = 6.83x10-16 - 3.68x10-14 J; Critical radii r* = 20- 72 nm. This experimental evidence strongly support the early stage growth model of silicon quantum dot deposited on corning glass substrate.
A STUDY ON SINTERING BEHAVIOR AND MECHANICAL PROPERTIES OF HIGH SPEED STEEL POWDER THROUGH POWDER METALLURGY ROUTE
High speed steel (HSS) is a common material used in the manufacturing of cutting tool and other cutters. In this study, M3/2 HSS had been used to produce cutting tool insert through powder metallurgy (PM) route. The HSS was mixed with iron phosphorus (Fe3P) powders in a turbula mixer for 30 minutes by dry blending. The powder mixtures were than consolidated into green compact and sintered in the range of 1100 °C – 1225 °C under nitrogen-hydrogen atmosphere. Further work was done through heat treatment process to improve the mechanical properties of the insert. The properties were determined through hardness testing, transverse rupture strength (TRS) and the specimens were metallographic examined using Scanning Electron Microscopy (SEM). Based on the test result, it could be concluded that the optimum temperature for sintering process of M3/2 HSS + 9% Fe3P is 1200 °C.
GAS SENSING BEHAVIOR OF ZINC OXIDE NANORODS SYNTHESIZED VIA HYDROTHERMAL METHOD
Zinc oxide (ZnO) nanorods were grown on silicon substrate by simple hydrothermal method in an aqueous solution of mixed zinc nitrate hexahydrate (Zn(CH3COO)2.2H2O) and hexamethylenetetramine (C6H12N4, HMT). The nature of the substrate was found to have effect on the crystal structure and morphology of the grown ZnO nanorods. Pre deposited ZnO nanoparticles on the substrate were serving as seed layer to grow ZnO nanorods. The vertically aligned ZnO nanorods were obtained by well controlling the concentration of aqueous solution and substrate temperature. The sensing behavior of grown ZnO nanorods was measured at room temperature using oxygen gas. The resistance of device is greatly changed when exposure to the oxygen gas indicates that ZnO nanorods have a potential gas sensing behavior.
STRUCTURAL AND SURFACE CHARACTERIZATION OF COLD DEPOSITED ZINC SULFIDE THIN FILMS
Zinc sulfide thin films with the thickness of about 0.5 μm were deposited using a thermal evaporation system onto oxidized silicon substrates at cold temperature (Tcold = –50 oC) and at ambient temperature (Tambient = 25 oC). A special substrate holder with a thermoelectric cooler was used to cool the substrates. The crystalline structure and the morphology of the films were investigated by X-Ray Diffraction and atomic force microscopy, respectively. XRD results show that the structure of the cold deposited ZnS thin film was completely amorphous. The ambient deposited ZnS thin film has a mixture of amorphous structure and polycrystalline structure with the preference orientation of (111) plane. The crystallite size of ambient deposited ZnS thin film was about 10 nm as calculated using the Scherrer formula. The AFM analysis revealed that the estimated grain size of cold deposited and ambient deposited ZnS were about 360 nm and 1220 nm, respectively. The surface roughness of the cold deposited ZnS thin film was greater than the surface roughness of the ambient deposited ZnS thin film.
SYNTHESIS OF HIGH-LUMINESCENCE CdSe QUANTUM DOTS AT VARIOUS TEMPERATURES
The aim of this paper is to investigate the effect of temperatures on the optical properties of CdSe quantum dots (QDs). High-luminescence CdSe QDs were synthesized using wet chemical method via thermal decomposition reaction of organometallic cadmium and selenium as precursors in a hot solvent mixture. Cadmium precursor was prepared in the three-neck flask with the mixture of CdO, 1-octadecene and oleic acid as a stabilizer. 1 mL of selenium precusor which was prepared earlier was quickly injected into the flask at the temperature between 260oC to 310oC. CdSe quantum dots were grown for 45 seconds and then immediately collected. The resulting QDs were isolated by centrifugation and redispersed in hexanes. The optical properties of quantum dots were characterized using Photoluminescence spectrometer (PL) and UV-Vis Spectrometer. When the QDs exposed under the UV-lamp, it radiated light from green to red colour, indicating an increment in the size as the growth temperature increased. PL test revealed that the emitted wavelength of QDs were in the range of 500 nm to 650 nm with the narrow peak. UV-VIS spectrometer characterization support the PL characterized about the emission and excitation of electron which contributed the information on energy gap of the QDs. The effect of temperatures on the improvement of the optical characteristics of CdSe QDs will be discussed.
SINTERING AND MECHANICAL PROPERTIES OF MgO-DOPED HYDROXYAPATITE BIOCERAMICS
In the present research, nano hydroxyapatite (HA) powder doped with magnesia (MgO) was studied. The dopant was added to pure HA powder and ball milling was done for 1 hour. Green samples, in the form of discs and rectangular bars, were prepared and consolidated in air at temperatures ranging from 1000 °C to 1300 °C. The sintered samples were characterized to determine the phase stability, relative density, hardness, fracture toughness and Young’s modulus. The phase analysis revealed that the HA phase was not disrupted regardless of dopant additions and sintering temperature. It has been revealed that all HA samples achieved > 98% relative density when sintered between 1100 ºC - 1300 ºC. However, the addition of 0.5 wt% MgO when sintered at 1100 °C was found to be most beneficial in aiding sintering with samples exhibiting the highest Young’s modulus of 122.15 GPa and fracture toughness of 1.64 MPam1/2 as compared to 116.57 GPa and 1.18 MPam1/2 for the undoped HA.
SHORT RANGE STRUCTURE OF SODIUM CALCIUM PHOSPHATE GLASS BY INFRARED AND RAMAN SPECTROSCOPY
The aim of this study is to determine the influence of CaO and Na2O in the short range structure of metaphosphate composition. Sodium calcium phosphate glasses were prepared using melt quenching technique. The crystallinity of the samples was measured using XRD, while the short range structures were measured by IR and Raman spectroscopy. There is no crystalline phase detected from XRD analysis. This result shows that the prepared samples are glasses. Both IR and Raman results show that the main structure unit presents are composed of Q2 (middle) and Q3 (branching) tetrahedral units. The Q2 units were modified by the presence of Na and Ca ions while the spectrum showed that the P=O become weaken with the increasing of Na content. The spectral shifted to lower frequency at the asymmetric vibration (O-P-O) as Na2O is replaced by CaO. The asymmetric stretching band of (P-O-P) shifted to higher frequency with the substitution of CaO for Na2O. It is obviously show that the addition of modifier of CaO and Na2O changed the structure features of metaphosphate glass composition
EFFECT OF PRESSURE ON ELASTIC PROPERTIES OF CHITOSAN
The work focused on studying the elastic properties of chitosan composite system. The samples were prepared in form of compressed pellets. The structure and elemental analysis of chitosan was characterized using Fourier Transform Infrared Spectroscopy (FTIR). The FTIR spectra have been recorded in the spectral range from 280-4000cm-1. The velocity of sound of chitosan is obtained by the ultrasonic pulse-echo measurements, at room temperature. Both longitudinal and transverse velocities of chitosan are pressure dependence. From the value of density, longitudinal and shear ultrasonic velocity, the value of longitudinal modulus (L), shear modulus (G), bulk modulus (K), Young modulus (E) and Poisson ratio (σ) were calculated. The sound velocity increases as the density and pressure increase. The elastic modulus and Poisson’ ratio show increasing trend as the pressure of sample increases. The elastic modulus increases due to the compactness of the pressed sample. As the pressure and density increase, the atoms in chitosan became more compact thus the ultrasonic waves are dispersed between the atoms resulting in more propagation of wave.