Lingchao Cao

One-dimensional growth mechanism of amorphous boron nanowires

Abstract High-density of arrays of self-oriented boron nanowires grown on silicon substrates were synthesized by radio-frequency magnetron sputtering with a target of highly pure boron and boron oxide mixture using argon as the sputtering atmosphere. TEM studies show that the conventional growth mechanisms such as Frank screw-dislocation mechanism and the vapor–liquid–solid mechanisms are not suitable for the one-dimensional growth of boron nanowires. The oxide-assisted cluster–solid mechanism for the Si and Ge crystalline nanowires is not completely suitable for our case. The vapor–cluster–solid mechanism is proposed for the well-aligned growth of the amorphous boron nanowires.

Controlled growth of single-walled carbon nanotubes at atmospheric pressure by catalytic decomposition of ethanol and an efficient purification method

By using an originally designed chemical vapor deposition chamber, high-quality single-walled carbon nanotubes (SWNTs) have been synthesized over Fe–Co/MgO catalyst by catalytic decomposition of ethanol at atmospheric pressure. The as-synthesized carbon material primarily consists of the SWNTs bundle with few defects and a certain amount of amorphous carbon. By adjusting the concentration of ethanol solution, we can control diameter distribution of the SWNTs. We suggest that both addition of water and the designed setup play important roles for the controlled growth of SWNTs. After the efficient purification combining hydrochloric acid treatment, reflux of nitric acid and air oxidation, 98% purity of the SWNTs is obtained.

Nucleation and growth of feather-like boron nanowire nanojunctions

Nanojunctions made from one-dimensional nanostructures could provide fascinating opportunities to reveal new mesoscopic physics and could offer huge technological potential as well. Here we report highly controlled fabrication of boron nanowire nanojunctions with unilateral feather-like morphology by radio-frequency magnetron sputtering of a boron and boron oxide mixture in argon atmosphere. The branched boron nanowires nucleated on the same sidewall of the stems, grew airwards, and aligned in parallel to form multiple T- and/or Y-type nanojunctions. The boron nanofeathers self-assembled into large-scale, highly ordered arrays on various substrates without the use of patterned catalysts. This process might enable the creation of nanometre-size heterojunctions of a wide variety of one-dimensional nanostructures.

Boron nitride nanotube branched nanojunctions

One-dimensional boron nitride (BN) nanotube nanojunctions are of great interest for both fundamental and applied research because of their stable and excellent mechanical and physical properties. Large quantities of highly pure BN nanotube multiple Y- and/or T-junctions were synthesized by annealing pure boron nanowire precursors in N-2 atmosphere at 1500 degrees C. Transmission electron microscopy and electron energy-loss spectroscopy studies reveal that the products possess a concentric tubular structure and stoichiometric BN composition. The boron nanostructured precursors react with nitrogen at high temperature to form the corresponding BN components, retaining their original morphologies. A non-equilibrium interdiffusion of nitrogen and boron might be involved in the transformation process of the solid boron nanowires to hollow BN nanostructures. Our results illustrate the technological potential of BN nanoscale multiple junctions being incorporated into future nanoscale mechanical and electronic devices.

Fabrication and characterization of molecular scale field-effect transistors

Molecular electronics are considered one of the most promising ways to meet the challenge of micro-electronics facing its scaling down pathway. Molecular devices, especially molecular scale field-effect transistors (MSFET), are key building blocks for molecular electronics. Three major hurdles to device fabrication are yet to be overcome: electrode pairs must be fabricated with a controllable gap size commensurate with the functional molecule size of interest; the molecules of interest must be arranged between the electrodes with precise location and orientation control; and stable, conducting contacts must be made between the molecules and the electrodes. We have combined “top-down” and “bottom-up” approaches to solve these problems. Using photolithography and molecular lithography with self-assembled mono/multiple molecule layer(s) as a resist, we fabricated electrode structures with a controllable molecular-scale gap between source and drain electrodes and a third terminal of a buried gate. For our device, we synthesized a thiolated phthalocyanine derivative molecule, {di-[1-(S-acetylthio)-4-ethynylphenyl]-di-(tert-butyl)phthalocyanato}copper(II), with acetylthio groups on both ends, conjugated with ethynylphenyl groups. The synthesized end-thiolated molecules were assembled between the tailored molecular gap of the as-fabricated FET electrode structures in solution via Au–S bonding, forming stable contacts between the electrodes and the molecules, and a 3 terminal MSFET device was formed. Electrical measurements show that the device has characteristics of a typical FET device. The field-effect mobility of the as-fabricated MS-FET is 0.16 cm2 V−1 s−1.

Wet Purification of Aligned Carbon Nanotube Arrays and Its Impact on the Morphology of the Carbon Nanotube Arrays

Abstract A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.

Template-free synthesis of single-crystalline cadmium nanotubes

By pyrolysis of CdS powder in inert gas, single-crystalline cadmium nanotubes growing in the form of a heap, were produced for the first time in high yield.