Thin Solid Films 435 (2003) 318–323 0040-6090/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0040-6090Ž03.00341-9 Density control of carbon nanotubes using NH plasma treatment of Ni 3 catalyst layer Jong Hyung Choi , Tae Young Lee , Sun Hong Choi , Jae-Hee Han , Ji-Beom Yoo *, a a a a a, Chong-Yun Park , Taewon Jung , SeGi Yu , Whikun Yi , In Taek Han , J.M. Kim a b b b b b Center for Nanotubes and Nanostructured Composites, Sungkyunkwan University, 300, Chunchun-Dong, Jangan-Gu, Suwon 440-746, a South Korea FED projects, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, South Korea b Abstract The effect of NH plasma pre-treatment on the growth characteristics of CNTs was investigated. We observed that NH plasma 3 3 pre-treatment etched and conglomerated Ni catalyst film, resulting in the formation of Ni nanoparticles. The aligned CNTs from the Ni nanoparticles were grown by plasma enhanced chemical vapor deposition (PECVD). As Ni film thickness decreased from 300 to 30 A, the size of Ni nanoparticles decreased about from 140 to 90 nm and the average diameter of CNTs became smaller. ˚ As the NH plasma power was increased, the density of Ni nanoparticles was decreased, leading to the decrease in the density of 3 CNTs.  2003 Elsevier Science B.V. All rights reserved. Keywords: Carbon nanotubes; NH plasma pre-treatment; Ni nanoparticles; Density control 3 1. Introduction CNTs have attracted great attention because of their unique physical properties such as high mechanical strength and thermal stability and electronic properties w1,2x. Because CNTs have high electron emission effi- ciency at low voltage due to high aspect ratio, CNTs have been regarded as the most efficient electron emitter among various materials. For application as an electron emitter, the density control of CNTs including the control of length and diameter of CNTs is required because of the screening effect. Although, the diameter and length can be easily changed by the catalyst layer thickness, the control of CNTs density is reported to be very difficult w3,4x. A method such as an electron-beam lithography and photolithography technique can be used to control the CNT. However, high cost hinders the application of these techniques to large area field emis- sion display. There are many methods for synthesis of CNTs. Especially, plasma enhanced chemical vapour deposition (PECVD) method has been reported as one of the most *Corresponding author. Tel.: q82-31-290-7413; fax: q82-31-290- 7410. E-mail address: jbyoo@yurim.skku.ac.kr (J.-B. Yoo). promising candidates for the synthesis of CNTs due to the low temperature growth, vertical alignment and large area growth w5,6x. Plasma etching of catalytic layer in PECVD system can be applied to the density control of CNTs through the density control of catalytic particle. In this study, we used NH plasma pre-treatment to 3 form Ni nanoparticles. NH plasma pre-treatment of Ni 3 layer was adoped to control the size and density of Ni nanoparticles. CNTs were grown on the Ni nanoparticles. The density and growth characteristics of CNTs were investigated. 2. Experiments NH plasma pre-treatment was used to make a Ni 3 nanoparticles. Ni catalytic layer was deposited on the Cr coated substrate using magnetron sputtering. The thickness of Ni layer was changed from 30 to 300 A. ˚ The Cr buffer layer of 1500 A was deposited on the ˚ substrate by magnetron sputtering to prevent a reaction of the metal catalyst with the Si substrate. The metal coated substrate was transferred to the reaction chamber and pumped down below 2=10 Torr by a rotary y3 pump. After the pressure was stabilised and substrate