Growth of ALIGNED carbon nanotubes on Silicon by RF-plasma assisted Pulsed-Laser deposition

Y. K. Yap*, M. Yamaoka, M. Yoshimura, Y. Mori, T. Sasaki

Department of Electrical Engineering

Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.

Tel: +816-6879-7707 Fax: +816-6879-7708

Email: yap@ssk.pwr.eng.osaka-u.ac.jp

T. Hanada

Electron Microscope Laboratory, Institute of Science and Industrial Research

Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 565-0847, Japan

H. Furuta, T. Hirao

Department of Electrical Engineering

Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.

S. Honda and K. Oura

Department of Electronics Engineering

Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.

Abstract

Single walled CNTs are commonly grown by physical vapor techniques like laser ablation and arc discharge in inert gas ambient. These CNTs are free standing and mixed of carbon impurities. Likewise, large scale, vertically aligned multi-walled CNTs can be grown on various substrates by chemical vapor deposition (CVD) techniques. To date, the growth mechanism and parameters that differentiate the formation of single-walled and multi-walled CNTs in physical- and chemical vapor techniques are still not being established. Fundamental knowledge about the present and absent of hydrogen in CVD, laser ablation and arc discharge techniques are still unclear.

In pulsed-laser deposition (PLD), the growth ambient can be either vacuum or with inert gases, oxygen, hydrogen etc. So, it is possible to establish some understanding about the influence of gas ambient on the formation of CNTs if one can grows CNTs by the PLD technique. In this work, we present the first report on growing vertically aligned CNTs by means of a physical vapor deposition. We have grown vertically aligned multi-walled CNTs on Si(100) substrates by RF-plasma assisted PLD. Our CNTs are grown by using Fe catalysts at 800℃. These CNTs are 200-400 nm in length and about 50 nm in diameter. The density of such CNTs is estimated by a field emission scanning electron microscope (FESEM) as about 5 x 10⁷ cm^-2. Such density is at similar order of magnitude like those typically grown by CVD techniques. Some CNTs on our sample are as long as 1 mm. These tubes appeared to be highly uniform in diameter along the whole tube. High-quality graphite microstructures are indicated as also confirmed by the high-resolution transmission electron microscope (HRTEM).

Our deposition system consists of a solid-state UV laser (fifth harmonic generation of Nd:YAG lasers at a wavelength of 213 nm) with pulse duration of 3 ns. This laser beam is focused on a rotating graphite target with an intensity of 0.27 GWcm^-2. The carbon plume generated from such ablation is the only carbon source for the deposition of CNTs on the treated Si substrates attached on a heater 4 cm away from the target. The formation of CNTs depends strongly on the laser intensity (deposition rate), configuration of RF-plasma, substrate bias voltage and the synthesis gas ambient. The type of catalyst and way of processing the catalytic nanoparticles appeared to be crucial for the formation of such CNTs in our technique. Details of these results are to be presented in the conference.

Keywords: carbon nanotubes; catalyst; Fe, RF-plasma; pulsed-laser deposition;