Advanced Materials Research Vol. 545

Abstract: Drug discovery from natural products resources have been extensively studied. The most important step in the discovery process is the identification of compounds with interesting biological activity. Single crystal X-ray structure determination is a powerful technique for natural products research and drug discovery in which the detailed three-dimensional structures that emerge can be co-related to the activities of these structures. This article shall present (i) co-crystal structures, (ii) determination of absolute configuration and (iii) the ability to distinguish between whether a natural product compound is a natural product or a natural product artifact. All these three properties are unique to the technique of single crystal X-ray structure determination.

Abstract: Close observation with a transmission electron microscope (TEM) and a scanning electron microscope (SEM) was performed for the growth process of tin (Sn) whiskers on lead (Pb)-free Sn-plating. Whiskers were formed on a Sn layer plated on Cu/polyimide flexible substrate. The whisker was found to be of a single crystal and have a characteristic "Y"-shaped grain boundary structure at its root. The growth process of a curling whisker was successfully observed in a continuous way in SEM. TEM observation revealed that the curling whisker had a single crystallographic orientation irrespective with its external shape. these microstructures indicate that the rearrangement of dislocations plays an important role in the growth process of whiskers.

Abstract: An approach for making functional films of polymer – nanocomposites under the framework of nanotechnology is presented. In this methodology, nanowires of an inorganic functional material are dispersed in a functional polymeric medium and the resultant solution is developed into solid films by electrospinning technique. The final structure is a nanofibrous film – each nanofiber contains a percolating network of inorganic nanowires. The nanowires reduce the percolation threshold compared to those nanoparticles and maintain the flexibility and/or light weight of the polymers and nanomaterials. This methodology has been tested for a number of material architectures for electronic and energy devices.

Abstract: A group of perovskites with general formula A₂(RE,B)O₆ (A=Ba, Sr; RE=Rare-Earth; B=Sb, Zr) were synthesized as nanocrystals owing to the enhanced specific surface area that nanomaterials posses. These perovskites are characterized by varied crystal structure depends on the relative sizes of the cations occupying the A and B sites of the perovskite lattice. The new materials were either insulators or semiconductors. They possess moderate dielectric constant (~30) and relatively low dielectric loss (10^-4); and therefore, they could be used as substrates in microwave circuits. Some of them falls to the semiconducting range with band gap ~3.3 eV; and therefore, could be used as transparent wide band gap semiconductors. Furthermore, the new perovskites were found to be chemically stable with two mostly considered high temperature ceramic superconductors for practical applications, viz. YBa₂Cu₃O_7-δ (YBCO) and (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (BSCCO).

Abstract: Further study of the quantum dot potential under hydrostatic pressure for Si is presented. This potential has been calculated by means of our recent empirical model. The indirect energy gap (Γ-X) is calculated using the full potential-linearized augmented plane wave (FP-LAPW) method. The Engel-Vosko generalized gradient approximation (EV-GGA) formalism is used to optimize the corresponding potential for energetic transition and optical properties calculations of Si. The refractive index and transverse effective charge are predicted under pressure effect. The pressure effect is used to test the validity of our model. The results are compared with others and showed reasonable agreement.

Abstract: MgO thin films were deposited by Pulsed Laser deposition using different process parameter. The characteristics were investigated via X-Ray diffraction (XRD), Scanning Electron Microscope (SEM) and Digital Holographic Microscope (DHM). It is found that the thin film surface morphology and thickness are different. It was found that the different process parameters such as chamber gas pressure, substrate temperature, LASER energy and number of pulses greatly influence the characteristics of the thin films obtained. The thin films have very low thicknesses of 97, 187 and 193 nm.

Abstract: A brief review is presented of quasicrystal surfaces and their use as templates for exotic epitaxial structures. The review is illustrated with several examples from the work of the Liverpool quasicrystal group.

Abstract: This paper presents a new ignition technique to synthesize NiAl based composites using high frequency induction heating to ignite the combustion reaction. A high resolution thermal imaging camera and two infrared thermometers were used to monitor the complete temperature profiles during synthesis. Thermodynamic calculations were performed to predict the combustion temperature and the effect of preheating temperatures. The results show that the combustion reaction for Ni/Al based composites can be ignited using a high frequency induction heater. High density, multi layer TiC-NiAl composites can be produced using this method, but to ignite the combustion reaction by induction heating for the Ni/Al+Ti/C system, there is a limit for the content of Ti/C, above which the ignition will not start. Ultra fine TiC was synthesized using this technique.

Abstract: In this study, natural colours were produced from Melastoma Malabathricum L.’s (Senduduk) plant. The dyes were extracted from the petal part of the plant using solvent extraction method of acidified methanol and methanol. The natural colours were then converted into powder form of nano size scale using a ball mill grinder. Silk fabrics were used as the substrate and dyed using several natural and synthetic mordant. The use of different solvents for extraction and mordant for dyeing resulted in different colour shades on the silk fabrics. The color fastness to washing tests revealed colour fastness to washing ranging from 3 – 4/5 and the change in color ranging from 3/4 – 4/5. The findings will benefit and promote the dyeing and printing industry such as batik manufacturers and local fashion industry in using natural dyes. On the other hand, dyes from plants can also be used as an alternative to synthetic dyes for dyeing natural silk fibers.