Zhenping Zhou

Double wall carbon nanotubes promoted by sulfur in a floating iron catalyst CVD system

Double wall carbon nanotubes (DWCNTs) were mass-produced by pyrolizing C2H2 at the temperature range of 900–1100 °C on a floating iron catalyst with sulfur promoted. Our experiments indicated that the growth of DWCNTs was strongly dependent on the sulfur addition, and without sulfur only single wall carbon nanotubes (SWCNTs) were produced. The outer tube diameters of DWCNTs observed by high resolution electron microscopy (HRTEM) vary from 1.05 to 2.89 nm, and the inner tube diameters vary from 0.40 to 2.19 nm. The effect mechanism of sulfur to the growth of DWCNTs was discussed.

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.

Temperature dependence of resonant Raman scattering in double-wall carbon nanotubes

The temperature-dependent frequency shift of resonant Raman spectra of double-wall carbon nanotubes is investigated in the range of 78–650 K. We show here that different radial breathing mode (RBM) peaks, which are relative to different tube diameters, have a different temperature coefficient of frequency shift, and the larger diameter carbon nanotubes have more RBM frequency downshift with increasing temperature. We attribute the RBM frequency variation to the temperature dependence of the stretching force constant of C–C bond.

Characterization of zinc oxide crystal nanowires grown by thermal evaporation of ZnS powders

Abstract Semiconductor single-crystal ZnO nanowires have been successfully synthesized in bulk quantities by a simple and low cost process based on thermal evaporation of ZnS powders onto silicon substrates with the presence of Au catalyst. XRD of the product proves that the nanowires are the wurtzite structure of ZnO. Scanning electron microscopy and transmission electron microscopy show that the ZnO nanowires have diameters about 20–60 nm and lengths up to several tens of micrometers. The growth of ZnO nanowires is controlled by the conventional vapor–liquid–solid mechanism. The dependence of photoluminescence on temperatures was examined by He–Cd laser.

A simple large-scale synthesis of coaxial nanocables: silicon carbide sheathed with silicon oxide

Abstract We reported a simple method to synthesize coaxial nanocables with silicon carbide core and amorphous silicon oxide sheath just by exposure of Au-coated silicon substrates to carbon monoxide at 1100 °C. The as-grown product was characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and micro-Raman spectroscopy. The obtained nanocables were in large scale, several tens of micrometers long, with the core a few nanometers to ten or more nanometers in diameter. The vapor–liquid–solid mechanism was proposed to elucidate the growth process.

Producing cleaner double-walled carbon nanotubes in a floating catalyst system

We demonstrate that Fe impurities in double-walled carbon nantoubes (DWNTs) may be greatly depressed by improving the experimental setup in a floating catalyst CVD method. In the paper, the effect of different experimental parameters on sample purity has been systematically studied. The possible reasons for the decrease of impurity in the DWNT samples prepared with the improved apparatus are discussed. The process should be helpful for preparing high quality single- or double-walled carbon nanotubes in scale-up applications.

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.

Resonant Raman scattering of double wall carbon nanotubes prepared by chemical vapor deposition method

Resonant Raman spectra of double wall carbon nanotubes (DWCNTs), with diameters from 0.4 to 3.0 nm, were investigated with several laser excitations. The peak position and line shape of Raman bands were shown to be strongly dependent on the laser energies. With different excitations, the diameter and chirality of the DWCNTs can be discussed in detail. We show that tubes (the inner or outer layers of DWCNTs) with all kinds of chiralities could be synthesized, and a DWCNT can have any combination of chiralities of the inner and outer tubes.