Growth of carbon nanofiber coatings on nickel thin films on fused silica by catalytic thermal chemical vapor deposition: On the use of titanium, titanium-tungsten and tantalum as adhesion layers

Coatings of carbon nanofiber (CNF) layers were synthesized on fused silica substrates using a catalytic thermal chemical vapor deposition process (C-TCVD). The effects of various adhesion layers-titanium, titanium-tungsten and tantalum-under the nickel thin film on the attachment of carbon nanofibers and their morphological properties are presented. The diameter and the thicknesses of the CNF-coatings were analyzed by scanning electron microscopy, whereas the microstructure and crystallinity of the synthesized carbon nanofibers were investigated by transmission electron microscopy and Raman spectroscopy, respectively. Specific surface areas of CNF-coatings; were determined with nitrogen adsorption-desorption isotherm measurements. Using C-TCVD of ethylene at 700 degrees C (1 h), well-attached, entangled, quasi-crystal line platelet carbon nanofibers were synthesized with tip-type growth mode on 25 nm thick nickel films with an adhesion layer of 10 nm Ta or Ti-W. The thickness of CNF-coating was similar to 3.5 mu m, and the diameter of the fibers depended on the composition of the metallic thin film stack: 20-50 nm for Ni/Ta and 80-125 nm for Ni/Ti-W. The ultimate goal is the integration of these CNF-coatings as catalyst support in microfluiclic devices, for which it is important to control CNF-coating characteristics such as fiber diameter, layer thickness, specific surface area and adhesion to the surface. (C) 2009 Elsevier B.V. All rights reserved.