Atmospheric pressure microwave torch for synthesis of carbon nanotubes

Abstract

The microwave (mw) plasma torch at atmospheric pressure has been studied for carbon nanotube (CNT) synthesis. The depositions were carried out on silicon substrates with 5-15 nm thin iron catalytic overlayers from the mixture of argon, hydrogen and methane. The optical emission spectroscopy of the torch showed the presence of C 2 and CH radicals as well as carbon and hydrogen excited atoms. The vicinity of the substrate influenced the relative intensities and increased the emission of C 2 . For fixed mw power, the temperature of the substrate strongly depended on its position with respect to the nozzle electrode and on the gas mixture, particularly the amount of H 2 . The speed of the substrate heating during an early deposition phase had a significant effect on the CNT synthesis. An abrupt increase of the temperature at the beginning increased the efficiency of the CNT synthesis. Areas of dense straight standing CNTs, 30 nm in average diameter, with approximately the same sized iron nanoparticles on their tops were found in accordance with the model of growth by plasma enhanced chemical vapour deposition. However, the deposit was not uniform and a place with only several nanometres thick CNTs grown on much larger iron particles was also found. Here, taking into account the gas temperature in the torch, 3100-3900 K, we can see similarities with the 'dissolution-precipitation' model of the CNT growth by high temperature methods, arc or laser ablation.

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

“…Therefore, it also resulted in bulk production of unaligned CNTs [37,38]. However, we have shown that MW torch is capable of the high-speed synthesis of vertically aligned supported CNTs [39][40][41]. This paper provides a critical overview of the previous experiments, supplemented by recent improvements of the torch design and deposition procedure, discharge diagnostics, the study of catalyst phase, and effects of underlaying material.…”

“…Ferrite circulator protected the generator from the reflected power by re-routing it to the water load. Matching of the plasma load to the line impedance was achieved by a combination of a movable short plunger and a line stretcher as described in [39]. The coaxial line and the nozzle electrode accommodated a dual gas flow.…”

“…Recent optimization of the MW torch design led to few improvements as compared to the previously published papers [39][40][41]. A stub tuner was mounted to the waveguide for easiest load matching, and the design of the torch was modified in order to achieve better stability of torch discharge.…”

Synthesis of Carbon Nanostructures by Plasma Enhanced Chemical Vapour Deposition at Atmospheric Pressure

“…The experiments with microwave (mw) torches are focused on the floating catalyst approach (ferrocene, iron pentacarbonyl), ie , also bulk production of unaligned CNTs [10]. On the other hand, the mw torch has been successfully used by our group for high speed synthesis of vertically aligned supported CNTs [11][12]. With regard the dielectric barrier discharges (DBDs), Kyung, Lee et al .…”

Carbon nanotubes synthesized by plasma enhanced CVD: preparation for measurements of their electrical properties

“…The temperature of the substrate is measured by Raytek Thermalert TX pyrometer from its backside. More details of the microwave torch construction are given in [5].…”