Mechanism and optimization of metal deposition onto vertically aligned single-walled carbon nanotube arrays

Arrays of vertically aligned single-walled carbon nanotubes (VASWNTs) were coated with thin films of Ti, Pd, Au, and Al by evaporative deposition. Scanning electron microcopy showed the Ti and Pd coatings were continuous or quasi-continuous, whereas Au and Al agglomerated into discrete deposits on SWNT bundles. The mechanism of metal film formation on VASWNT arrays was studied by observing the film at various stages of the deposition process. Uniformity of the deposition was found to be strongly dependent on the metal species and the deposition conditions, such as substrate temperature, deposition rate, and deposition thickness. The optimization of the deposition conditions was demonstrated for Pd. The results suggest that the deposition efficiency for a smooth coating layer is determined by the balance of two processes with significantly different speeds: the coating along an SWNT bundle and coating of an interbundle, which depend on the metal type and the deposition conditions. These findings may be useful regarding both fundamental and practical aspects of VASWNT applications in thermal and electronic devices.