Solid State Phenomena Vols. 121-123

Abstract: Large-scale synthesis of In-doped SnO2 (ITO) nanowires was achieved by direct thermal evaporation of a mixture of Sn and In powders at 900°C in an Argon atmosphere. Scanning electron microscopy and transmission electron microscopy observations show that ITO nanowires have diameter ranging from 20 to 100 nm and lengths up to several tens of micrometers. By altered the reaction temperature, we find that the temperature of the reaction is the critical factor for the morphologies and sizes of the ITO nanowires.

Abstract: With an average diameter of 300-500 nm, conducting microspheres of polyaniline (PANI) were synthesized successfully by a self-assembly method in the presence of ferrocene sulfonic acid (FcSO3H) as the dopant, and ammonium persulfate ((NH4)2S2O8) as the oxidant. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) proved that the microspheres of PANI- FcSO3H synthesized by a self-assembly process were hollow ones. And the backbone structure of obtained PANI- FcSO3H was characterized by FTIR spectrum. The effect of synthetic conditions, such as the molar ratio of FcSO3H to aniline (An) and the reaction temperature, on the morphology and size was also investigated.

Abstract: A novel hollow sphere having rigid binaphthyl macrocycle as shell was prepared by means of sacrifice the silica core. The synthesis of hollow sphere from rigid colloidal silica particles occurs in three steps: a) modification of silica particles with vinyltriethoxysilane as coupling agent, b) immersion in the solution of monomer having rigid binaphthyl macrocycle and polymerization, and c) removal of silica particles. These macrocycles contained in the shell of hollow spheres belong to an important class of host-guest macrocyclic material in which the rigid backbone and C2 symmetry of the binaphthyl unit play an important role in complexing guest molecules. This will endow hollow sphere with new opportunities in molecular recognition and separation.The morphology of colloidal silica particles and hollow spheres was characterized by SEM and TEM.

Abstract: Ferroelectric lead zirconate titanate(PZT)thin films have attracted great attention because of their potential applications in memory devices[1] due to their unique properties, for example, hysteresis loop and high dielectric constant. To realize these memory devices, it is necessary to overcome the reliability problems such as fatigue, retention and imprint. It is well known that lead base perovskite family ferroelectric thin films with donor dopant such as La3+ and Nb5+ have improved the electrical properties of PZT thin films effectively [2-3]. And it is proposed that the cation substitution could reduce the number of defects such as oxygen vacancies, which could promote electrical fatigue and leakage current of PZT ferroelectric thin films obviously. In the present study, rare earth Yb-doped lead zirconium titanate (PYZT) nanocrystalline powders with a composition near the morphotropic phase boundary (Zr/Ti=52/48) were prepared by a modified sol-gel method. DTA/TG and XRD were used to determine the thermal and phase changes in the formation of PYZT crystalline powders. The effect of Yb3+ cation substitution for Pb2+ cation on the microstructure of PZT was developed with XRD. The grain size of PYZT nanopowders is about 40 nm determined by TEM.

Abstract: The interaction between gas atmosphere and silicon during reaction bonded silicon nitride(RBSN)process leads to a non-uniform band formation of alpha silicon nitride. The reaction layer, α -Si3N4, was formed near the surface of the sample in the early stage of RBSN. Reactive nitrogen gas was supplied as static state using computer controlled gas delivery system. The formation of α -Si3N4 band near the surface of the sample can be explained thermodynamically, based on the nitrogen partial pressure in the gas mixtures.

Abstract: Two-step acid-base catalyzed silica xerogels were prepared through sol-gel and ambient pressure drying. Various additive components were main fators which influenced the porosity of silica xerogles. An orthogonal array (OA) design OA9(34) was applied to select the optimum conditions of additives. The effects of the molar ratio of H2O, alcohol, HCl, and ammonia were evaluated on the basis of the other same process parameters. Every experiment was conducted several times under different process conditions which included reactive temperature, the acid catalyzed time, aging, exchanging solvent and drying for assuring gels formed. The porosity was an index which was used to appraise the characteristic of silica xerogels. Two kinds of silica xerogels, prepared by the most optimal molar ratio (OMR) and the best OA experiment respectively, were compared by means of SEM. The results showed that the most OMR of TEOS, H2O, alcohol, HCl and ammonia was 1:4:10:7.5× 10-4:0.0375.

Abstract: Nanoparticles of titanium dioxide co-doped with Fe3+ and Nd3+ were prepared using the sol-gel method. The prepared TiO2 photocatalyst was characterized with XRD, FTIR and the photocatalytic activity was evaluated by photodegradation of MB aqueous solution. Nanocrystalline TiO2 co-doped with Nd3+ and Fe3+ at optimal concents shows a synergistic effect, which significantly increases the photodegradation activity of TiO2.

Abstract: We present a prototype of thermal interface material (TIM) by incorporating aligned carbon nanotube arrays (CNA) into polydimethylsiloxane (PDMS). The morphology of CNA was maintained by adopting in-situ injection molding method, and the nanotube-polymer composite film was obtained by curing the PDMS at room temperature. We applied steady-state methods to measure the thermal conductivity of this kind of nanocomposite. Comparing to the pure PDMS, the thermal conductivity of the composite was greatly increased, which can be attributed to the thermal conducting passages formed by vertical aligned carbon nanotubes from one side of the film to the other. We also managed to improve the thermal conducting performance of the composite by evaporating a 1-μm-thick aluminum film on the top of a raw CNA, which serves as a heat current collector to decrease the thermal contact resistance. The experiment results suggest these kinds of composites have broad application prospect for thermal management in the future.