Advanced Materials Research Vols. 55-57

Abstract: In this paper, the straight and T-shape single-walled carbon nanotube intramolecular junction (SWCNT-IMJ) were studied theoretically. The geometries of topological defect can be constructed by fusing two nanotubes having different helicities and diameters. For straight IMJ, the armchair (5,5) and (8,8) nanotubes segments were fused with the zigzag (n,0) segment varying from (6,0) to (10,0). T-junctions were constructed by joining a zigzag (n,0) tube, varying from n = 5 to 10, onto a fixed zigzag (9,0) tube sidewall. These junctions are composed of one or more pentagon and heptagon rings, and mixed pentagon-heptagon pairs as defects in the perfect hexagonal lattice. The study shows that the occurrence of defects geometries on SWCNT-IMJ and T-shape structures depends on the variation of tube helicity and diameter of combining nanotubes. The HOMO-LUMO energy levels exhibit the even-odd “quantum size” oscillation. The decreasing energy gap depends on variation of tube helicity and diameter of carbon nanotube. This study can be helpful as a knowledge base in the field of carbon nanotube molecular electronics.

Abstract: Barium hexaferrite particles derived from sol-gel combustion method with a mean particle size of 160 nm and Fe particles with a mean particle size of 150 µm were mechanically alloyed using planetary ball mill. Phase constitution and EDS analysis of the products were investigated by XRD and SEM, respectively. Magnetic properties of samples were measured by VSM. Influence of the milling time and Fe content on the phase constitution of synthesized composites has been investigated. XRD results indicated that in sample with 90 and 50wt% Fe, the magnetic composite with enhanced magnetic properties, formed based on Fe phase while barium hexaferrite particles embedded within Fe particles. In sample with 90% Fe, the crystallite size of Fe reduced from 173 to 87 nm by increasing the milling time from 1 to 20 h; saturation magnetization of the 20 h milled sample was measured as 94.8 emu/g. Besides, in sample with 50wt% Fe, some FeO phase was detected which is probably due to the partial decomposition of hard magnetic phase during milling. Sample with 10wt% Fe showed completely different behavior and magnetite appeared as a major magnetic phase.

Abstract: The AlON films grown on Si(100) substrates by using radio frequency (r.f.) magnetron sputtering from high purity aluminum (99.999% Al) target with a novel reactive gas-timing technique. The 100 nm thick of AlON films were deposited with 200 watts r.f. power and the substrate temperature is maintained at room temperature by the technique of gas-timing which varying flow-in sequence of high purity of Ar (99.999%) and N2 (99.9999%) gases fed into the sputtering chamber at 10:90 (sec) ratio. The composition and crystal orientation of AlON films affected by gas-timing of Ar and N2 were analyzed by Auger Electron Spectroscopy (AES) and X-ray diffraction (XRD). The oxygen atoms revealed by AES formed into a corporation in films was studied. This suggests that the oxygen contamination formed as AlOXNY compound may due to the residual oxygen in base pressure of 10-7 mbar and higher reactivity of oxygen in the reactor compared to nitrogen. The gas-timing technique used in the sputtering growth system shows the advantage of the oxygen quantity control, while the general sputtering process (without gas-timing technique) shows an increase of the oxygen composition depended on film thickness. The characterizations results clearly indicate that the gas-timing r.f. magnetron sputtering technique plays an important role to control the incorporation of oxygen and to form the nanocrystal-aluminum oxynitride films which very attractive for various sensors applications.

Abstract: The photocatalytic decolorization of aqueous solutions of Direct Red 27 in the presence of various amounts of semiconductor powder suspensions has been investigated in a batch reactor with the use of artificial light sources. ZnO and TiO2 have been found the most active photocatalysts; the effect of catalyst loading and type on the reaction rate was optimized for maximum degradation. The results imply that 1:1 ratio is proper for the photocatalytic removal of Direct Red 27. In addition, the effects of particle size and surface area were examined in this photocatalytic process. The results showed that the decolorization efficiency increases with increase in surface area, and decrease in powder size. The efficiency is related to mechanism of reactions on the active sites of the catalyst surface and broad adsorption of compounds with different band gaps

Abstract: Nb addition was found to be beneficial to the electrode properties of mechanically alloyed Mg2Ni-based product in 6M KOH solution. Formation of Mg2Ni-based nanocrystalites occurred after 15 and 5h of milling using the initial binary and ternary powder mixtures with stoichiometric compositions of Mg2Ni and Mg1.75Nb0.25Ni, respectively. Further milling of the ternary mixture resulted in the formation of an amorphous phase which became dominant after 30h. Negative electrode made from ternary product after 20h of milling exhibited the highest initial discharge capacity and the longest discharge life. This electrode showed to have a microstructure consisting of nanocrystalline Mg2Ni and an amorphous phase.

Abstract: Here we report the synthesis of nanoparticles with aspect ratios of up to five by synthesis in small concentrated volumes of reactants using an ink-jet printer. Silver and gold nanoparticles were synthesized rapidly on transparent sheets using a commercial ink jet printer. A commercial inkjet printer was modified by replacing conventional inks with different reactants including silver nitrate, ammonium-complex silver, gold chloride reduced by ascorbic acid. The reaction was allowed to occur directly on the substrate within a short reaction time and confined reaction volume defined by the droplet size on the substrate. The nanoparticles and microrods formed on the substrate depend on pH and ionic concentrations of the solutions. The pH of the solutions is an important factor controlling the aspect ratio of microrods. When the concentration of silver ions in the reactant solution was increased the number of particles deposited on the substrate increased subsequently. Anisotropic particles could be formed uniformly over very large area surfaces (1mm x 20mm). This method can be suitable for rapid synthesis of anisotropic particles for potential application in metal-enhanced fluorescence sensing, antibacterial coating, anti reflection coatings, amongst others.

Abstract: The synthesis of fluorescent nanocrystals is receiving a lot of attention for potential application in biological labeling as well as phosphors for field emission devices. Zinc sulphide doped with manganese (ZnS:Mn2+) is one of the most efficient electroluminescent phosphor displaying a wide emission band centred around 590 nm resulting from the intra-ionic transition in Mn2+ ions. We report a unique synthesis of zinc sulphide nanoparticles doped with manganese using a biocompatible passivating agent ‘chitosan’, with bright luminescence peaking at 590 nm. This high luminescence efficiency of the synthesized nanocrystals are ideal for quantum dot based bio-labeling applications. Synthesis of the nanoparticles was carried out by precipitation reaction in aqueous media of zinc acetate and sodium sulphide where manganese acetate was added as the dopant. The obtained nanoparticles were around 4 to 6 nm in size and were found to be stable for months of shelf life. The photoluminescence intensity did not degrade when the colloid was heated up to 65 oC for prolonged periods.

Abstract: Thin films of Nickel Phthalocyanine (NiPc) are prepared at a base pressure of 10-6 mbar using Organic Evaporator System. The films are deposited onto the glass substrate at various temperatures of 100 0C, 120 0C, 140 0C and 160 0C. Crystalline of NiPc thin films was investigated by X-ray diffraction (XRD) spectroscopy. XRD patterns exhibit to become aggravated crystalline films as monoclinic structure. Surface morphology of NiPc thin films was characterized by field emission scanning electron microscope (FE-SEM). FE-SEM micrographs indicate that fiber-like morphology of NiPc is enhanced with increasing substrate temperature. The optical absorption spectra of these thin films are measured. Present studies reveal that the Q-band of NiPc thin films appears as the change of electron energy level. Absorption spectra obtained from UV-vis of deposited NiPc are declined as the substrate temperature is risen.

Abstract: Diamond-like carbon (DLC) films have been deposited on silicon substrates using microwave plasma enhanced chemical vapor deposition (PE-CVD) process of CH4 in H2 gas mixture. The well-faceted good quality DLC film with distinct diamond Raman spectroscopic characteristics are found at low CH4 concentration. Schottky barrier diode (SBD) structures are fabricated onto the grown DLC films using Ti/Au and Al as ohmic and rectifying contacts, respectively. The responses of DLC-SBD to DC and time varying signals have been studied. The frequency dependent response results are compared to models, which includes as input parameters the depletion and bulk regions resistances and capacitances trap effects, and SBD parameters of which extracted from the DC I-V characteristics. It is found that the frequency dependent properties of DLC-SBD can be associated with deep trap states inside the DLC material rather than with only the SBD geometrical structure.

Abstract: Red colored gold ruby glass used for decorations in ancient times was actually gold nanotechnology at work by the addition of gold particles into molten lead glass. Most of high refractive index glasses are based on lead-bearing silicate glass. High refractive index lead glasses (HRLG) made from local sands and lead oxide were successfully fabricated both in laboratory and larger scales. In this study, gold metal was doped into the lead glass mixtures. Morphology of the prepared lead glass was observed using SEM and compared with that of the red colored Ancient Thai Glass (ATG). It was found that the fabricated red colored HRLG yielded similar color and clarity to the red colored ATG. From electron micrographs, the presence of gold in lead glass was in the form of nanoparticles. The optical properties of the glasses were also examined.