Deposition of vertically oriented carbon nanofibers in atmospheric pressure radio frequency discharge

Abstract

Deposition of vertically oriented carbon nanofibers (CNFs) has been studied in an atmospheric pressure radio frequency discharge without dielectric barrier covering the metallic electrodes. When the frequency is sufficiently high so that ions reside in the gap for more than one rf cycle (“trapped ions”), the operating voltage decreases remarkably and the transition from a uniform glow discharge to an arc discharge is suppressed even without dielectric barriers. More importantly, the trapped ions are able to build up a cathodic ion sheath. A large potential drop is created in the sheath between the bulk plasma and the electrode, which is essential for aligning growing CNFs. At the same time, the damage to CNFs due to ion bombardment can be minimized at atmospheric pressure. The primary interest of the present work is in identifying the cathodic ion sheath and investigating how it influences the alignment of growing CNFs in atmospheric pressure plasma-enhanced chemical-vapor deposition. Spectral emission profiles of He (706nm), Hα (656nm), and CH (432nm) clearly showed that a dark space is formed between the cathode layer and the heated bottom electrode. However, increasing the rf power induced the transition to a nonuniform γ-mode discharge which creates intense plasma spots in the dark space. Aligned CNFs can be grown at moderate input power during the initial stage of the deposition process. Catalyst particles were heavily contaminated by precipitated carbon in less than 5min. Alignment deteriorates as CNFs grow and deposition was virtually terminated by the deactivation of catalyst particles.

Carbon Nanotube Synthesis in Atmospheric Pressure Glow Discharge: A Review

“…To date, APG has made remarkable progress in formation techniques; various types of APGs and related applications have been constructed for many purposes. Actually, APG is useful not only for improving the productivity of industrial applications, but also for the synthesis of functional materials such as carbon nanotubes,12–14 diamond‐like carbon,15 ultrahigh‐speed etching,16 silicon oxide nanoparticle deposition,17 and amorphous/crystalline silicon film deposition 18, 19. All have been investigated extensively in the scope of APG.…”

“…We have specifically addressed single‐walled carbon nanotube (SWCNT) synthesis in APG 12–14. Although plasma‐enhanced chemical vapor deposition (PECVD) is recognized as a viable synthesis method, carbon nanotubes (CNTs) synthesized in low‐pressure PECVD are overwhelmingly carbon nanofibers (CNFs) and multi‐walled carbon nanotubes (MWCNTs):20, 21 SWCNTs had not been realized in the scope of low‐pressure PECVD until recently.…”

Plasmachemical synthesis in low-temperature atmospheric pressure plasma

“…Comparison of the results of synthesis of carbon nanotubes in atmospheric pressure DBD and RF (13.56 MHz) plasmas [91,111] showed that in the first case no carbon nanotube arrays formed, while in the second case at the same temperature (700°С) quality arrays of vertically aligned carbon nanotubes could be obtained. Moreover, according to [111], atmospheric pressure RF plasma has symmetric regions of a cathodic ion sheath and a dark space.…”

“…Syntheses can be performed in reactors with a plane parallel electrode configuration. Substrates may be placed both directly in the plasma region [93,111] and beyond this region (socalled remote plasma processes) [112][113][114][115][116][117][118]. Certain tasks seem to be better solved in reactors with coaxial electrodes [119].…”

Synthesis of carbon nanotubes by plasma-enhanced chemical vapor deposition in an atmospheric-pressure microwave torch

“…The most successful application of DBD, in this case its glow mode (atmospheric-pressure glow), was performed by Nozaki et al It has been shown that vertically aligned SWNTs grow in RF atmospheric-pressure glow (APG) discharge using He/H 2 /CH 4 feed [32]. This result revealed the importance of a catalyst NP preparation for the achievement of SWNTs because Nozaki et al reported formerly the growth of unaligned CNTs of low quality in APG driven at 125 kHz [33] and the growth of CNFs in RF APG [34].…”