Controlled Synthesis of Carbon Nanowalls for Carbon Channel Engineering

Abstract

This study investigates the growth mechanisms of carbon nanowalls (CNWs), which are two-dimensional carbon structures that consist of stacked graphene sheets and that stand vertically on substrates. Factors that determine their morphological and electrical properties were studied using two plasma-enhanced chemical vapor deposition (PECVD) systems that permit the densities and energies of radicals and ions to be precisely controlled. For CNW growth using a C2F6/H2 plasma, the CNW growth rate decreased when the total pressure was increased from 13.3 to 80 Pa during growth. Raman spectroscopy and scanning electron microscopy revealed that the CNW crystallinity increases and the CNW density decreases with increasing total pressure. This is attributed to an increasing amount of H radicals in the growth ambient with increasing total pressure. During the initial stages of CNW growth using a multibeam PECVD system with CFx, hydrogen radicals, and Ar ions, CNWs were formed only for Ar+-ion fluxes of 3.3 to 3.8 A/cm2 and energies of 200 to 250 eV. Although attachment of CFx radicals and CNW growth require ion bombardment, if the flux or energy of ion bombardment is too high CNW growth will be inhibited due to etching and excessive carbon deposition. Semiconducting CNWs with n-type characteristics can be formed by adding N2 gas to the C2F6/H2 plasma. Furthermore, carrier concentrations of n-type CNWs can be controlled by nitrogen doping.