Synthesis of Carbon Nanotubes by Microwave Plasma Enhanced CVD on Silicon using Iron as Catalyst

Abstract

Carbon nanotubes (CNTs), the fourth allotropic form of carbon were discovered by Iijima in 1991. They have diameters on the order of a few nanometers and length in the micrometer range. This large aspect ratio (l/d) (>1000) renders them unique and is responsible for their extraordinary mechanical, electrical, chemical and electronic properties. Proposed applications of CNTs include high strength composites, flat panel displays, hydrogen storage, scanning probe microscopy tips, transistors, interconnects in IC. To realize their immense potential, CNTs need to be grown economically on a large scale and integrated into devices. In the present investigation microwave plasma enhanced chemical vapor deposition (MPECVD) technique is used to grow carbon nanotubes on silicon using iron as catalyst. Critical process parameters, such as source gas concentration, pretreatment time of catalyst film and growth time are varied and their effect on nanotube growth is studied. A template is used to grow CNTs on patterned blocks. SEM, TEM, AFM and -Raman Spectroscopy are used to characterize the carbon nanotubes. Vertically aligned carbon nanotubes with uniform diameter are successfully synthesized using MPECVD on a silicon wafer using iron as catalyst. Nanotubes are grown on patterned blocks. Improvement in alignment is observed with increase in methane flow rate. The optimum flow rate of methane is between 20 and 30 sccm. Entire catalyst coated area has deposition with increase in pretreatment time. Growth time of 5 min with methane flow rate of 15 sccm and 5 min of pretreatment time is optimum for obtaining vertically aligned CNTs. Using TEM micrographs the diameters of the nanotubes were determined to be 20-125 nm. ?-Raman spectroscopy indicate that carbon nanotubes are multi-walled.