http://meetings.aps.org/Meeting/4CF13/

1. http://meetings.aps.org/Meeting/4CF13/Session/K4.3  "Atomic Layer Deposition of Tungsten on Carbon Nanotubes" Jason Anderson , Collin Brown , David Allred

Microelectromechanical systems (MEMS) fabrication traditionally uses the same limited methods and materials as those used in the silicon-based microelectronics industry. In order to make MEMS out of a richer suite of materials, such as metals, Brigham Young University researchers are investigating chemical vapor deposition and atomic layer deposition of patterned carbon nanotube (CNT) forests, using the surface of the carbon nanotubes as nucleation sites for metal deposition. Our goal has been to fill in spaces between CNTs by atomistic deposition, thus creating a CNT-composite material possessing the original pattern of the CNT forest. We have attempted to do this using tungsten hexafluoride and hydrogen. As deposited the materials are not pure metals, but contain substantial amounts of carbon and oxygen. Most recently tungsten fluoride via both CVD and ALD is being used to attempt creation of purer tungsten structures. Efforts to remove impurities as well as the electrical and mechanical properties of the resulting composite material will be reported.

2.  http://meetings.aps.org/Meeting/4CF13/Session/K4.4  The low-pressure, chemical vapor deposition of Si02 layers using CO2 as the oxygen source with applications to CNT-MEMS growth,  Kenneth Hinton, Branton Mckeon & Allred

Deposited silica (SiO2) has a number of applications for microfabricated structures, particularly those based on coating carbon nanotube forests. Members of our group have, for example, reported on the fabrication and use of SiO2-coated carbon nanotube forests (CNT-MEMS) to prepare liquid chromatography plates of record efficiency. SiO2 also has extremely low thermal conductivity and stiff, coated, carbon nanotube forests could be used as thermal barrier layers. We have examined two novel methods for the LPCVD of SiO2 and oxygen-rich amorphous silicon. Both methods are based on the hypothesis that carbon dioxide could be used as the source of oxygen in preparing the material. In the case of oxygen-rich amorphous silicon (a-Si:O) we used silane as the silicon source, and the case of SiO2 used dichlorosilane. We deposited the a-Si:O material at about 800K while the Si02 from SiH2Cl2 , was deposited at about 1000 K. Depositions were done at low pressure, about 200 millitorr for the a-SI:O and at about 1 to 4 Torr for the SiO2. The substrates in all cases were three-inch single-crystal silicon wafers. We subsequently examined the deposited material using variable-angle, spectroscopic ellipsometry (VASE-John A. Woollam M 1000) for of thickness and optical constants and SEM structure and composition. The dichlorosilane deposition of SiO2 suffered from vanishingly small deposition rates at very low pressures at 1000 K and the incorporation of ``snow'' into the films in the case of depositions done at higher pressures. We found little evidence of carbon incorporation.