Nianzu Wu

Preparation of colloidal solutions of thin platinum nanowires

Colloidal solutions of thin platinum nanowires having lengths of 10 to 70 nm and diameters of 1.5–3 nm were prepared by reducing K2PtCl4 with hydrogen in a glycol solution containing K2C2O4 and preformed Pt seeds. TEM, HRTEM, XRD and UV-Vis absorption spectroscopy were used to study the structure of the obtained nanowires and the effect of preparation conditions, such as pH value, temperature, preformed Pt nanoseeds and stabilizing agents, on the morphology of the products. The mechanism for forming the thin Pt nanowires in the absence of a 1D structure template was discussed based on the experimental results. Stable colloidal solutions of mercaptan-modified Pt nanowires were prepared for the first time by transferring the prepared thin Pt nanowires into toluene containing octadecylmercaptan.

A study on the monolayer dispersion of tungsten oxide on anatase

The monolayer dispersion of tungsten oxide on the surface of anatase has been studied by BET surface area measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transformation infrared spectroscopy (FTIR) and Raman spectroscopy. The results reveal that for the anatase supported tungsten oxide samples, tungsten oxide species can be highly dispersed on the surface of the support and the dispersion state of tungsten oxide species is strongly related to the loading amount of tungsten oxide. In addition, it is found that tungsten oxide can retard the anatase–rutile transformation. When the loading of WO3 is below its monolayer dispersion capacity, the onset temperature of the anatase–rutile transformation is strongly affected by the dispersed tungsten oxide. Crystalline WO3 appears when the WO3 loading is higher than the monolayer dispersion capacity but has little effect on the phase transformation of the samples.

The study of the attachment of a single-walled carbon nanotube to a self-assembled monolayer using X-ray photoelectron spectroscopy

A chemical approach was put forward to organize the randomly tangled single-walled carbon nanotubes (SWCNTs) on a gold surface. The SWCNTs were highly organized on gold, forming a monolayer structure. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was employed to study the spatial structure of the monolayer of SWCNTs. The adsorption kinetics of the nanotubes was studied by measuring the thickness of the samples prepared at different immersion times. It was found that a SWCNTs monolayer could not form for a short period of immersion time. When prepared for a long enough period of time, the well-ordered monolayer of SWCNTs could form and remain stable.

Micropatterns constructed from Au nanoparticles

Covalently linked Au-NPs micropatterns have been successfully fabricated from the self-assembly film composed of 4-mercaptophenol-capped Au nanoparticles (Au-NPs) and -N2+ containing polymers of nitro-diazoresin (NDR) by selective exposure to UV light and development in sodium dodecyl sulfate (SDS) aqueous solution. The resultant well-defined micropatterns were characterized with AFM and XPS.

Diffusing behavior of MoO3 on Al2O3 and SiO2 thin films

By means of XPS, SIMS, synchrotron radiation excited total-reflection X-ray fluorescence, AES etc., the diffusion process of MoO3 on stable Al2O3 and SiO2 oxide thin films was investigated. After thermal treatment, MoO3 formed a monolayer or a submonolayer on the flat surface of the thin films. The diffusion capacity and the diffusion rate on these two kinds of films differ significantly. Besides the support used, several factors, such as the heating temperature, the heating time and the ambience influence the diffusion process. A possible explanation to all the phenomena is the combination of surface diffusion and transportation via gas phase.

Study of monolayer dispersion of MoO3 on muscovite powder and diffusing behavior of MoO3 on muscovite wafer by SR-TXRF

The dispersion capacity of MoO3 on the surface of muscovite powder was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. The results indicated that MoO3 can disperse onto the surface of a support as a sub-monolayer. The dispersion capacity was 5.88 mg MoO3 (g muscovite)−1, or 3.24 Mo atoms nm−2. The diffusing process of MoO3 on muscovite wafer was investigated by means of Synchrotron Radiation excited Total-reflection X-Ray Fluorescence spectroscopy (SR-TXRF). A stripe of MoO3 on the muscovite wafer was used as the diffusion source. After thermal treatment in air or dry N2, MoO3 diffuses onto the surface of muscovite and forms a sub-monolayer. Sublimation of MoO3 was also detected during the diffusion process. The diffusion rate in two heating atmospheres differed significantly. The diffusion rate of MoO3 on muscovite in dry N2 was greater than that in air. A possible explanation of the phenomena is that surface diffusion onto the muscovite surface plays a more important role in the process than transportation via gas phase during the diffusion of MoO3.

PREPARATIVE AND STRUCTURAL STUDIES ON THE SUPERCONDUCTING PHASE YBa2Cu3O7−d

Reasonably homogeneous samples were obtained by following the formula Y_(0.334)Ba_(0.666)CuO_(3-y) andusing citric acid as a complex-forming agent to improve the dispersion of the metal oxides. We havealso found that the variant condition in preparative procedure leads to variant deviation from tetrago-nality and that more pronounced deviation gives better superconducting properties. The crystal structure determined from X-ray powder diffraction diagrams confirms the stoichiom-etry of the metal ions and gives the positions of the oxygen atoms. The orthorhombic or pseudo-tetragonal unit cell with a=3.893, b= 3.813 and c= 11.687 A contains YBa_2Cu_3O_7. It is composed ofthree perovskite cubes with three copper atoms at their corners, the two barium atoms at the centers ofthe top and bottom cubes, and the yttrium at the center of the unit cell. The oxygen atoms sit on centersof cube edges. The positions (0 0 1/2) are vacant. The vacancies represented by (0(1/2)0) cause the ar-rangement of atoms to lose tetragonal symmetry, and have far-reaching effect for this phase. The yttriumand barium atoms are coordinated in a cuboctahedron respectively with four equatoria oxygen atoms at(0 0 1/2) and two at (0 1/2 0) removed. In the light of bond valence theory we can infer from the in-teratomic distances Y-O, Ba-O and Cu-O that the occupancy of the oxygen atoms at (1/2 0 0) is wellbelow unity while the positions (0 0 1/2) are vacant, the formula of the phase is YBa_2Cu_3O_(7-d), thefraction of Cu(Ⅱ) and (Ⅲ) for the set of copper at (0 0 0) is respectively d/0.5 and (1-d/0.5), and0.2d0.4. The other set of copper is a normal bivalent one.

Self-assembly and photoelectric properties of cerium complexes with 3, 4, 9, 10-perylenetetracarboxylic acid on nanocrystalline TiO2 films

Self-assembled (SA) films (PMP, M = Ce3+ or Ce4+) of 3,4,9,10-perylenetetracarboxylic acid (PTA) on nanocrystalline TiO2 films with Ce3+ or Ce4+ as a bridge were fabricated and characterized with UV-Vis, IR, and XPS synchrotron radiation photoelectron spectroscopy (SRPES) which gave the HOMO energy levels for the SA films. It was shown that thin-layer sandwich-type solar cells based on these SA films possess good properties for photoelectric conversion. While PTA-loaded TiO2 electrode (P) generated 26.9% of incident monochromatic photon-to-electron conversion efficiency (IPCE), PMP-sensitized TiO2 electrodes yielded 55.8% and 39.1% for Ce4+ and Ce3+ respectively. PMP films can be considered as a kind of complexes whose HOMO energy levels were proved to be higher than that of film P, which is one of the major reasons for the increase in IPCE from film P to film PMP.