Junfeng Geng

Gold catalyzed growth of silicon nanowires by plasma enhanced chemical vapor deposition

Silicon nanowires were selectively grown at temperatures below 400 °C by plasma enhanced chemical vapor deposition using silane as the Si source and gold as the catalyst. A detailed growth study is presented using electron microscopy, focused ion beam preparation, and Raman spectroscopy. A radio-frequency plasma significantly increased the growth rate. The Si nanowires show an uncontaminated, crystalline silicon core surrounded by a 2-nm-thick oxide sheath. The as-grown diameters are small enough for the observation of quantum confinement effects. Plasma activation could allow a further decrease in deposition temperature. A growth model for plasma enhanced nanowire growth is discussed.

Crystal Structure and Growth Mechanism of Unusually Long Fullerene (C60) Nanowires

Exceptionally long C60 nanowires, with a length to width aspect ratio as large as 3000, are grown from a 1,2,4-trimethylbenzene solution of C60. They have been formed to possess a highly unusual morphology, with each nanowire being composed of two nanobelts joined along the growth direction to give a V-shaped cross section. The crystal structure of these nanowires is found to be orthorhombic, with the unit cell dimensions of a = 10.2 A, b = 20.5 A, and c = 25.6 A. Structural and compositional analyses enable us to explain the observed geometry with an anisotropic molecular packing mechanism that has not been observed previously in C60 crystal studies. The nanowires have been observed to be able to transform into carbon nanofibers following high-temperature treatment, but the original V-shaped morphology can be kept unchanged in the transition. A model for the nanowire morphology based upon the solvent-C60 interactions and preferential growth directions is proposed, and potentially it could be extended for use to grow different types of fullerene nanowires.

CVD synthesis of carbon nanotubes

Abstracts are not published in this journal

Characterization of carbon nanotube–thermotropic nematic liquid crystal composites

Dispersions of carbon nanotubes (CNTs) in liquid crystals (LCs) have attracted attention due to their unique properties and possible applications in photonics and electronics. However, these are hard to stabilize, and the loading level in the equilibrium state in LC hosts is small. A practical way to monitor the quality and CNT incorporation in such equilibrium dispersions is required. Here, we compare different methods for characterising equilibrium CNT–LC composite materials.

The unusual nanostructure of nickel-boron catalyst

A highly unusual nanostructure of the nickel-boron particulate material, initially synthesised in the 1950s and well known to be an exceedingly active hydrogenation catalyst, has been identified for the first time.

Submicron patterning of Co colloid catalyst for growth of vertically aligned carbon nanotubes

Applications of carbon nanotubes such as field emission or microelectrode sensor arrays require a patterning of vertically aligned carbon nanotubes over large areas. A highly purified and concentrated monodisperse cobalt colloid was produced for use as a catalyst for growth of carbon nanotubes. Nanocontact printing was employed to deposit the cobalt nanoparticles in regular patterns with feature sizes at the 100?nm scale onto silicon wafers at low cost over large areas. Vertically aligned carbon nanotubes were grown by direct current plasma enhanced chemical vapour deposition at temperatures ranging from 300 to 640??C.

Direct conversion of iron stearate into magnetic Fe and Fe3C nanocrystals encapsulated in polyhedral graphite cages

We report a direct salt-conversion approach for large-scale synthesis of carbon-encapsulated magnetic Fe and Fe3C nanoparticles.

Synthesis of high purity single-walled carbon nanotubes in high yield

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.

Exploring the structural complexities of metal-metalloid nanoparticles: the case of Ni.B as catalyst.

Understanding of the structural complexities of metal-metalloid nanoparticles is at the heart of several proposals for investigating the physical properties and practical applications of these bi-elemental nanomaterials. To date, the most widely studied metal-metalloid is the nickel-boron (Ni.B) system; however, the exact nature of the structure of the material itself has remained unclear. Herein we show our systematic investigations of the material in an attempt to reveal its fascinating nanostructure. The relation between its high catalytic activity and the ultrafine structure is explored, and the work has been further extended to the formation of colloidal Ni.B nanoparticles. The results presented in this work may represent a substantial progress toward a full understanding of the nickel-boron chemistry.

Fullerene-based one-dimensional crystalline nanopolymer formed through topochemical transformation of the parent nanowire

Large-scale practical applications of fullerene (C60) in nanodevices could be significantly facilitated if the commercially-available micrometer-scale raw C60 powder were further processed into a one-dimensional (1D) nanowire-related polymer displaying covalent bonding as molecular interlinks and resembling traditional important conjugated polymers. However, there has been little study thus far in this area despite the abundant literature on fullerene. Here we report the synthesis and characterization of such a C60-based nanowire polymer, (-C60TMB-)n, where TMB=1,2,4-trimethylbenzene, which displays a well-defined crystalline structure, exceptionally large length-to-width ratio and excellent thermal stability. The material is prepared by first growing the corresponding nanowire through a solution phase of C60 followed by a topochemical polymerization reaction in the solid state. Gas chromatography, mass spectrometry and 13C nuclear magnetic resonance evidence is provided for the nature of the covalent bonding mode adopted by the polymeric chains. Theoretical analysis based on detailed calculations of the reaction energetics and structural analysis provides an in-depth understanding of the polymerization pathway. The nanopolymer promises important applications in biological fields and in the development of optical, electrical, and magnetic nanodevices.