Factors determining properties of multi-walled carbon nanotubes/fibres deposited by PECVD

Abstract

This paper presents a number of factors which have been found to be important to the growth of carbon nanotubes and nanofibres by plasma enhanced chemical vapour deposition. The effect of the electric field in a plasma discharge on nanotube growth is investigated and shown to be important in achieving nanotube alignment. The use of a plasma discharge also enables deposition to take place at lower temperatures, facilitating the use of substrates which would otherwise be damaged. The effect of varying the ratio of carbon feedstock gas to etchant gas is investigated and the ratio is shown to be important for controlling the shape of deposited nanostructures. The effects of varying plasma power are investigated, showing that greater plasma power results in a lower growth rate. Higher levels of plasma power are also shown to cause the sidewalls of deposited carbon nanotubes to be etched. Finally, the growth rate of carbon nanotubes and nanofibres is shown to depend upon the strength of the local electric field. It is proposed that a higher field causes greater ionization within the plasma, which results in a higher growth rate. This is borne out by comparing simulation results with experimental observations.

Investigating the plasma chemistry for the synthesis of carbon nanotubes/nanofibres in an inductively coupled plasma-enhanced CVD system: the effect of processing parameters

“…Our results show that the N 2 flux is predominant beside the NH 3 flux, especially for a low C 2 H 2 fraction(less than 20%). Hence, this might explain why in many papers [7][8][9]12] the C 2 H 2 /NH 3 mixture is used for CNT/CNF growth rather than the C 2 H 2 /H 2 plasma. The DRs of the background gas molecules in the C 2 H 2 -containing plasmas are displayed in figure 8 (a) for the C 2 H 2 /H 2 plasma and in figure 8(b) for the C 2 H 2 /NH 3 plasma.…”

“…A series of systematic studies was performed by Milne and coworkers [7][8][9] on the CNT growth process conditions by dc-PECVD, using a C 2 H 2 /NH 3 gas mixture. The growth properties (such as growth rate, diameter, length and density of the CNTs) were studied as a function of the Ni catalyst layer thickness (0.5~9 nm), bias voltage (0~-600V), deposition temperature (550~900°C), C 2 H 2 :NH 3 ratio (where the molar fraction of C 2 H 2 varied from 20% to 75%) and pressure (0.2~10Torr) [7].…”

Vertically aligned carbon based varactors

“…The conditions of the warm-up step determine how the catalyst seeds are converted to catalyst nanoparticles. 97,98 After the warm-up step and while the NH 3 ambiance was maintained, the plasma was ignited and the plasma current was set to 20 mA. The ammonia-plasma treatment continued for two minutes during which the temperature of the sample was set to increase from 500 C to 700 C (the same temperature slope as before).…”

Formation of Nanostructured Relief of TiN—Fe Heterostructures in Hybrid Helicon-Arc Plasma Reactor

“…It should be noted that for the date an activated plasma-enhanced chemical vapour deposition (PECVD) is the only deterministic CNT growth technology, which allows us to control a position, size, shape, and structure of CNTs at a certain extent and synthesize CNTs at lower temperatures [3][4][5]. Main technological operations in PECVD process to provide high-quality CNT synthesis are: 1) deposition of diffusion barrier sublayer; 2) formation of nanostructured films of metal catalyst; 3) synthesis of CNTs.…”