Xinyuan Dou

Growth mechanism of silver nanowires synthesized by polyvinylpyrrolidone-assisted polyol reduction

Silver (Ag) nanowires with a pentagonal cross section have been synthesized by polyvinylpyrrolidone (PVP)-assisted polyol reduction in the presence of Pt nanoparticle seeds. The UV–visible absorption spectra and scanning electron microscopy have been used to trace the growth process of the Ag nanowires. X-ray photoelectron spectroscopy investigation further shows that the PVP molecules are adsorbed on the surface of the Ag nanowires through Ag : O coordination. Comparing with the growth process of Ag nanoparticles, a possible growth mechanism of the Ag nanowires has been proposed. It is implied that the PVP molecules are used as both a protecting agent and a structure-directing agent for the growth of Ag nanowires. It is concluded that the five-fold twinning Ag nanoparticles are formed through heterogenous nucleation after the introduction of Pt nanoparticle seeds and then grow anisotropically along the 110 direction, while the growth along 100 is relatively depressed.

Growth of ZnO hexagonal nanoprisms

We show the success of large-scale growth of ZnO hexagonal nanoprisms on silicon substrates by a two-staged mechanism. In the first stage, the catalyst nanoparticles assisted the nucleation via the vapour–liquid–solid (VLS) mechanism to form polyhedral nanoparticles. In the second stage, the nanoprism was grown up by anisotropic homoepitaxy, layer by layer, on the c-face of the polyhedral nanoparticle. The surface of the nanoprism consists of the ultraflat {0001} and planes. The nanoprism is 200–500 nm in width and controllably sized in length, of high crystalline quality and excellent optical quality. This nanoprism would be an interesting building block for highly efficient nanolasers.

Template-free synthesis of helical hexagonal microtubes of indium nitride

Single crystalline indium nitride (InN) helical microtubes with a hexagonal hollow cross section have been synthesized in bulk quantities by nitriding indium oxide powder in ammonia flux. As-prepared InN microtubes grow along the [0001] direction with typical outer diameters of 1–3μm, wall thickness of 50–80nm and lengths up to hundreds of microns. The InN microtubes exhibit both right-handed and left-handed helicities with helical angles ranging from zero to about 30°. Variation of helicity can be observed in a single tube. A number of observations demonstrate that the growth of the tubular structure occurs by the spiraling of the warped InN nanobelts. Photoluminescence spectrum of the microtubes presents a strong emission peak centered at 700nm at room temperature.

Electrochemical fabrication and structure of NixZn1−x alloy nanowires

NixZn1?x alloy nanowires were successfully prepared by the templated electrodeposition technique. The morphology and the microstructures of as-deposited nanowires were examined by scanning electron microscope, x-ray diffraction, transmission electron microscope and electron diffraction. It is demonstrated that the content of magnetic element Ni in the nanowires can be easily adjusted by changing the ingredients of the electrolyte, the deposited current density and the deposited voltage, which is critical to tune the magnetic property of the nanowires. X-ray diffraction and electron diffraction analysis indicate that the NixZn1?x nanowires exhibit different structures with the variation in the quantity of nickel in the nanowires. It is expected that these heterogeneous alloy nanowires will have a potential application in nanoscale giant-magnetoresistance devices.

Controllable preparation and properties of single-/double-walled carbon nanotubes

Abstract In this paper, we discussed recent studies done in our laboratories with a floating catalyst chemical vapor deposition (CVD) method. We can grow single- or double-walled carbon nanotubes (SWNTs/DWNTs) with different kinds of catalysts. Single-walled carbon nanotubes without amorphous carbon coating were prepared by thermally decomposing acetylene (C2H2) at the temperature range of 750–1200 8C with ferrocene as catalyst. While with sulfur promoted ferrocene catalyst, double-walled carbon nanotubes were mass-produced by pyrolizing C2H2 at the temperature range of 900–1100 °C. Furthermore, tunable growth of DWNTs with different diameter was achieved in our experiment. It is found that DWNTs produced at lower carbon partial pressure have much smaller inner tubes, even DWNTs with the smallest inner diameter of 0.4 nm was found in here. As convenient and effective tool, radial breathing mode (RBM) of Raman scattering technique can be used to distinguish SWNTs from DWNTs. In further studies of Raman scattering with DWNTs, the possible match of the inner tubes and the outer tubes according to the RBM bands was assigned, and different chirality types were discussed according to the diameter and chirality dependence of resonant Raman vibration. We also investigated the temperature-dependent frequency shift of resonant Raman spectra of DWNTs in the range of 78–650 K. We found that different RBM peaks, which are relative to different tube diameters, have different temperature coefficient of frequency shift, and the larger diameter carbon nanotubes have more RBM frequency downshift with increasing temperature. It is ascribed to the RBM frequency variation to the temperature dependence of the stretching force constant of C–C bond. Besides, Polarized Raman spectra were preformed on well-aligned SWNTs structure fabricated through post-growth method and found that the angular dependence of Raman intensity is consistent well with the predictions of the resonance Raman theory.

Anodizing behavior of aluminum foil patterned with SiO2 mask

SiO 2 -Patterned anodic aluminum oxide (AAO) is fabricated on the surface of aluminum (Al) foil by combining both photolithography and anodizing technique. Tilted pores and ridge-like features on the Al surface are observed under the SiO 2 mask by scanning electron microscopy characterization. A mechanism based on the deflection of electric field due to the existence of SiO 2 barrier on Al surface has been proposed to explain the observed anodizing behavior. Moreover, large-scale ordered metallic Al patterns are also revealed by removing the AAO film and SiO 2 mask.

Patterned anodic aluminium oxide fabricated with a Ta mask

Electrochemical anodization was applied to an aluminium (Al) sheet patterned with a metallic tantalum (Ta) mask, which gave rise to the formation of patterned anodic aluminium oxide (AAO). The morphological evolution of the AAO porous structure with anodizing time was characterized by scanning electron microscopy. Lateral anodizing of the Al sheet gradually developed underneath the metallic Ta mask with the increase of anodizing time. This has given us further understanding of the Al anodizing behaviour compared with our previous work with a SiO2 masked Al sheet. By controlling the anodizing time and the size of the metal mask, deep lithography of the Al substrate can be realized, and a mushroom-like Ta–Al microstructure with a high aspect ratio was created on the Al surface after removal of the AAO film. This Ta–Al microstructure has been studied in detail, and it was found to exhibit pronounced hydrophobic properties.