Advanced Materials Research Vol. 620

Abstract: Solidvapor deposition was used to synthesize nanocrystalline PbS thin films on a Si (100) substrate. Lead sulfide (PbS) powder was first prepared and then heated to 1050 °C in a tube furnace. The resulting vapor was carried to the substrate zone by an argon flow. The structure of the nanocrystalline PbS thin films was determined by X-ray diffraction (XRD). The grain size of the PbS thin films and powder was also estimated by XRD. The surface morphology and stoichiometric ratio of these ingots were observed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy. The SEM image revealed that the film had a uniform surface morphology over the entire substrate. The optical absorbance of the deposited films and powder were measured by Fourier-transform infrared spectroscopy. The optical band gap E_g of the samples was calculated using the Tauc formula. The absorption of the thin films was found to be higher than that of the powder and lower for the entire wavenumber range (15005000 nm). The E_g values of the films determined were 3647 nm (0.34 eV), and that of the powder was 3100 nm (0.40 eV).

Abstract: Nanoparticles of Cobalt-zinc ferrite (Co_0.5Zn_0.5Fe₂O₄) and Cobalt-manganese ferrite (Co_0.5Mn_0.5Fe₂O₄) have been synthesized at room temperature by co-precipitation method with and without calcination process. Starting materials for preparation of nanooxides were Co (NO₃)₂.6H₂O, ZnCl₂, Fe (NO₃)₃.9H₂O and Mn (NO₃)₂.4H₂O. These salats were mixed in stoichiometric amounts and precipitated with sodium hydroxide. Synthesised materials are confirmed by XRD and SEM analysis. The FTIR spectra of nanooxides have been analyzed in the frequency range of 400-4000cm^-1.

Abstract: The effects of calcium carbonate (CaCO₃) addition on the physical properties of ZnO-based crystal glaze batches were investigated. Samples were fired at different gloss firing temperatures ranging from 1180-1220°C with 3 hours soaking at 1060°C crystallization temperature. X-ray diffraction (XRD) analysis identifiedthe crystal phase occurred as willemite (Zn₂SiO₄) and the scanning electron microscope (SEM) analysis indicated that willemite crystals are in the acicular needle like shape that formed spherulite. The intensities of willemite peaks decreased with CaCO₃ addition and completely vanished at 5.0 wt% CaCO₃. Varied formation of spherulites developed of the surface of crystal glaze as the flows of the glaze stretched further as the amount of CaCO₃ increased.

Abstract: Multilayer structure of porous silicon was fabricated using electrochemical etching method. Average thickness of multilayer structure was verified. Surface morphology from Atomic Force Microscopy (AFM) shows that surface roughness was decreased when higher etching time applied to the samples. Si 2p binding energies were corresponded to the composition of void within the silicon which prompted the formation of porous silicon nanostructure. Depth profiling technique from X-Ray photoelectron spectroscopy (XPS) was used for compositional determination of porous silicon layers since samples porosity varied according to current density applied during the electrochemical etching process. Multilayer porous silicon is a high potential candidate for Bragg grating waveguide device.

Abstract: This paper focuses on the compositional and structural characterization of InGaN-based light-emitting diode (LED) using high resolution x-ray diffraction (HRXRD) system. The LED was epitaxially grown on Si (111) substrate that comprises of In_0.11Ga_0.89N multi-quantum-well (MQW) active layer. Phase analysis 2θ-scan proved the composition of GaN (0002) and (0004) at 34.63^o and 72.98^o, respectively. Rocking curve φ-scan showed six significant peaks of the hexagonal GaN structures with consistent angular gaps of ~60^o. From x-ray rocking curve (XRC) ω-scan, screw and mix dislocation density is found as 2.85 × 10⁹ cm^-2, while pure edge dislocation density is found as 2.23 × 10¹¹ cm^-2.

Abstract: The study reported here focuses on the crystallite size of synthetic hydroxyapatite (HAp) obtained using sol-gel method and natural HAp obtained by processing the natural bone. Human and camel bones were used for obtaining natural HAp. HAp particles were produced, characterized and compared for their crystallite size. The average crystallite size of the samples was derived from the X-ray Diffraction (XRD) data using the Scherrer formula and a new method called modified scherrer equation that was came by developing the Scherrer formula. The results showed the crystallite size of HAp gained from different sources were different. The crystallite size of synthetic, human and camel bone-derived HAp, were approximately 18, 23 and 29 nanometer, respectively. These values were less than those obtained from TEM images. It seems that calculated crystallite size using XRD data and Scherrer equations is less than the real size. This important finding must be taken into consideration in applying Scherrer equations.

Abstract: Fracture toughness and phases of ceramic composites produced from alumina, yttria stabilized zirconia and chromia oxide system was investigated. The Cr₂O₃ weight percent was varied from 0 wt% to 1.0 wt%. Each batch of composition was mixed, uniaxially pressed 13mm diameter and sintered at 1600 C for 4 h in pressureless conditions. Studies on on their mechanical and physical properties such as Vickers hardness and fracture toughness were carried out. Results show that an addition of 0.6 wt% of Cr₂O₃ produces the best mechanical properties. Results of the highest fracture toughness is 4.73 MPa.m^1/2,

Abstract: Porous silicon nanostructures light-emitting diode (PSiNs-LED) will be a device for future flat screen display and can be high in demand. Main purpose of this experiment is to determine the photoluminescence properties of porous silicon nanostructures (PSiNs). PSiNs samples were prepared using photo-electrochemical anodization. P-type silicon substrate was used for this experiment. For the formation of PSiNs, a fixed current density (J=20 mA/cm²) and 30 minutes etching time was applied for the variety of electrolyte volume ratio. Volume ratio of hydrofluoric acid 48% (HF48%) and absolute ethanol (C₂H₅OH), HF48%:C₂H₅OH, were used for samples 3:1, 2:1, 1:1, 1:2 and 3:1. The effective photoluminescence properties was observed for sample C.

Abstract: Owing to its great potential in optoelectronic devices, structural and surface properties of porous GaN prepared by UV electrochemical etching has been investigated. Scanning electron microscopy (SEM), atomic force microscopy (AFM) and high resolution X-ray diffraction (HR-XRD) phi-scan and rocking curves measurements revealed the nature of the pore morphology and nanostructures. SEM micrograph indicated that the shapes of pores for porous sample are nearly hexagonal. The AFM measurements revealed that the surface roughness increased in the porous sample. X-ray diffraction phi-scan showed that porous GaN sample maintained the epitaxial feature.