Study on the effects of hydrogen pretreatment on nickel catalyst used for multi walled carbon nanotube growth

We investigated the effects of hydrogen pretreatment on nickel catalyst of different thicknesses and deposition methods on a silicon substrate and how it will affect the growth of carbon nanotubes using microwave plasma enhanced chemical vapor deposition (MPECVD). Nickel catalyst of 10, 50, 100, 200, 350 and 500 Å thickness was treated with hydrogen flowing at 135 standard cubic centimeter per minute (sccm), substrate temperature of 400 °C, microwave power of 400 W, and pressure of 20 torr. The treated catalyst granule size and density was determined optically through scanning electron microscope (SEM) images and atomic force microscope (AFM) measurements. We found that sputtered catalyst needs a longer pretreatment than evaporated catalyst. As expected, the pretreatment time must be increased as the catalyst thickness increases to get granule sizes and densities favorable for carbon nanotube (CNT) growth. CNT growth took place with a hydrogen flow of 120 sccm, methane flow of 15 sccm, substrate temperature of 650 °C, microwave power of 1000 W and a pressure of 20 torr. We determined the catalyst can be over treated causing catalyst conglomeration that result in poor CNT growth.