Abstract
Since the carbon nanotube (CNT) arrays are widely used in field emission displays as electron sources, it is more and more important to grow high density and regularly arranged CNT arrays. In this study, we hope to control the structure of the porous silicon (PS) template so that we may control the CNT arrays structures. The current density, HF solution concentration and time are the parameters that affect the PS structure, which was prepared by electrochemical method. We changed different experimental parameters to find the optimal process conditions, and used SEM, four-point probe to analyze PS structures, and also, we grew the CNT arrays on the PS template.The SEM pictures showed that the depth of PS increased with time, HF solution concentration, and current density. Increasing the current density caused the pore density increased, but when time was longer, the pore density would decrease and pore diameters became lager due to lateral growth of pores. Increasing HF solution concentration tended to decrease the pore density, but with deeper columnar branching structures of smaller diameters. It was also found that the columnar structures could only grow on the silicon wafers with lower resistivity. Once the resistivity was higher, the PS channels grew with more branches and the structures became broken and irregular.The PS resistivities were measured by four-point probe. The results did not show good correlation with the PS structure and morphology. The EDX results had oxygen indication in the PS structure but not in the silicon crystal suggesting that high PS resistivities were attributed to silicon oxide (SiO2) formation.The PS templates were deposited with 10nm nickel catalyst with e-gun evaporation, followed by a thermal chemical vapor deposition (CVD) of carbon nanotube in a furnace of 750~8500C fed with 800 sccm 10%CH4. The porous structure was apparently beneficial to the synthesis of carbon nanotube compared to the amorphous spherical carbon on non-porous silicon. In some cases, vertically aligned carbon nanotubes were observed along the edge of nickel film on porous templates.