Patterning and Characterization of Carbon Nanotubes Grown in a Microwave Plasma Enhanced Chemical Vapor Deposition Chamber

This research studies the growth of carbon nanotubes (CNT) from a nickel catalyst to be used on a field emission device. This thesis can be divided into three sections: the construction of a vacuum chamber for field emission testing, the design and fabrication of a triode structure to enable improved electron emission, and the pretreatment and growth of CNTs. To experimentally test the field emission of CNTs, a vacuum chamber must attain a vacuum of at least 10-5 torr. Our vacuum chamber designed and built achieved a maximum, final pressure of 10-8 torr. A triode structure was designed to pattern the CNTs to improve electron emission. A silicon wafer is used to fabricate the cathode and gate of the device while a quartz wafer is used as the anode. Through photolithography patterning of the gate, CNT growth occurs only in the defined locations. To better understand CNT growth, a study was performed using a hydrogen pretreatment on sputtered and electroplated nickel catalyst on silicon at various thickness in a microwave plasma enhanced chemical vapor deposition to determine the effects of this pretreatment. Nickel catalyst of 50, 100, and 200 ºA were treated with hydrogen and the formation of nano islands was achieved when using sputtered films. As the nickel catalyst thickness increases, the pretreatment time must also be increased to get favorable granule sizes and densities necessary for CNT growth. The 50 and 100 ºA nickel samples granulated to 25 and 58 nm showed high growth densities while the 200 ºA samples granulated to 180 nm showed marginal CNT growth. We also established the diameter of the multi walled CNTs grown correlated well to the size of the catalyst granules. The CNTs to be used in the triode design needed to be between 1.5 and 1.8 µm to avoid shorts between the gate and the CNTs. To achieve this, CNTs with a length of 1.5 µm were successfully grown by flowing methane for exactly two minutes

Effects of Hydrogen Pretreatment on Physical-Vapor-Deposited Nickel Catalyst for Multi-Walled Carbon Nanotube Growth

Physical vapor deposited nickel catalyst layers of 10, 50, 100, 200, 350, and 500 angstroms were granulated using hydrogen plasma for varying times to determine an effective carbon nanotube (CNT) growth process using microwave plasma enhanced CVD (MPECVD). Nickel was deposited via sputtering or evaporation. The catalyst granule size, density, and resulting CNTs were analyzed. Sputtered nickel of 50 angstroms with 5 minutes of hydrogen plasma pretreatment resulted in the most effective CNT growth.Abstract © SPI

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