Time dependent growth of vertically aligned carbon nanotube forest using a laser activated catalytical CVD method

Abstract

We report the growth of vertically aligned single‐wall and multi‐wall carbon nanotube forest using a Laser Activated – Catalytic Chemical Vapor Deposition process. The experiments were performed in a cold‐wall reactor filled with an ethylene‐hydrogen‐argon gas mixture in a 5:2:8 ratio at ambient pressure. A near infrared continuous wave laser diode was focused on a flat specimen to promote a local carbon nanotubes growth. Si substrates coated with a 20 nm Al2O3 layer on which a 2 nm thick Fe film was deposited were used. Growth products are characterized using Raman spectroscopy and Scanning Electron Microscopy. In this paper, we specifically discuss the influence of the laser exposure time on the growth process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Laser-assisted growth of carbon nanotubes—A review

“…In fact, the laser type and wavelength could influence the resulting growth. Apart from the most commonly used CO 2 lasers, a wide variety of different laser sources have been reported to grow CNT structures, such as Ar-ion lasers, 80,81,91,96 Nd:YAG lasers, 78,92,97 diode lasers, 76,[98][99][100] and Nd:YVO 4 lasers. 77,78,93,94 These reported laser sources all are CW lasers where the beam irradiates the substrate continuously for a certain duration.…”

“…Generally, not the complete substrate is heated so using a thermocouple or conducting another physical measurement of temperature within the laser affected zone is not possible. However, if the locally heated area is large and sufficiently uniform 73,74,87 or if the thermocouple is close enough, 98 a first approximation of the growth temperature can be obtained.…”

“…The early reports used Fe(CO) 5 as catalyst precursor, 73,74,79,86,87 but iron has been reported most. 78,93,94,[98][99][100][101]107 The control of catalyst morphology allows for a better control of the process, although there has not been a significant advantage of laser-assisted CVD over other CVD methods with respect to catalyst morphology control. In fact, the nonuniform temperature distribution most likely results in nonuniform size distribution of the formed nanoparticles and consequently a larger variety of CNT diameter and chirality.…”

“…74 They showed films of vertically aligned multiwalled carbon nanotubes of extremely high packing density. Later, Halu ska et al grew vertically aligned single-walled and multiwalled carbon nanotube forests 98 and Bock et al reported on radially aligned multiwalled CNT structures. 78 Also large mats of aligned carbon nanofibers were reported.…”

Co-catalytic Absorption Layers for Controlled Laser-Induced Chemical Vapor Deposition of Carbon Nanotubes

“…Chemical vapor deposition (CVD), in which CNTs nucleate and grow from catalyst nanoparticles exposed to hydrocarbon precursors at elevated temperatures, has become the dominant growth technique due to its versatility and scalability. To enable CMOS back-end compatibility and direct CNT integration on temperature-sensitive flexible substrates, a range of local heating strategies have been explored, in particular laser-induced CVD (LiCVD). − An opaque absorption layer is widely used for effective local heating in combination with high laser powers. − ,,− More controlled CNT LiCVD requires a detailed understanding of the catalytic growth process and the related laser interactions. Crucial to this, albeit widely neglected in the current literature, are process-specific increases in optical absorption arising from initial reduction of the transition-metal nanoparticle catalysts typically used, such as Fe, and the ever increasing amount of carbon deposited.…”