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Controllable Sequential Low Temperature Plasma Assisted Growth of Vertical Multi-wall & Single-wall CNTs

Z. Kolahdouz, S. Darbari, S. Mohajerzadeh
University of Tehran, IR

Keywords: CNTs, PECVD, sequential hydrogenation, S/M/WNT

Abstract:

By investigating the effects of growth parameters of CNTs, we have arrived at small diameter, single/multi-wall nanotubes at low temperatures. Synthesis of CNTs was performed using the gas mixture of the C2H2/CH4 gas and H2 in a DC-PECVD reactor. The physical properties of samples were investigated by HR-SEM, TEM and Raman spectroscopy. The studied parameters were temperature, hydrogenation time, plasma power and catalyst layer thickness. Moreover, a novel sequential hydrogenation/growth process has been developed. CH4 was found more suitable than C2H2 to achieve SWCNTs with widths of 10nm and less. Prior to CNT growth, Ni (1-13nm thickness), as the catalyst seed was conditioned using a sequential process. A dual-step pre-growth treatment of the surface was performed. First, the surface of the sample was treated with a hydrogen-blow for 15 min with the substrate temperature at ~550-700℃, followed by a treatment of hydrogen plasma at the same temperature of the growth in order to create Ni nano-islands. To avoid Ni-grain agglomeration we developed a new method of hydrogenation consists of several sequences of methane flow to temporally passivate the grains to keep the sizes unchanged. Immediately after the two-step pretreatment, CH4 was introduced into the chamber for 12 min to initiate the growth of CNTs.
 
 
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