Adherent carbon-based films exhibiting high electrical conductivity

Electrically conductive adherent films are useful for electrodes and microheaters. Carbon-based films of thickness ranging from 1 to 13 μm, with electrical resistivity ranging from 6.0 ×10^-4 to 3 Ω.cm were produced on an alumina substrate, using as the carbon precursor the combination of EPON SU 2.5 epoxy (with a lower viscosity than previously used EPON SU8 epoxy) and an amine curing agent, and a carbonization temperature of 650°C. This precursor, plus solvent and/or filler(s), gave carbon films without cracks and with good edge definition, in contrast to the poor edge definition when either polyamide or amidoamine (with low amine hydrogen equivalent weights) was used instead of the amine as the curing agent. Interconnected filamentary nickel nanoparticles were more effective for conductivity enhancement than silver nanoparticles (not filamentary) at the same volume fraction (5 vol.% or below). Multiwalled carbon nanotubes were between nickel and silver in their effectiveness. They were less effective than nickel nanoparticles in spite of their high aspect ratio. Even the combined use of nanotubes and silver nanoparticles was less effective than nickel nanoparticles alone. The filler volume fractions are much lower than those in prior related work, and are therefore attractive for good bonding to the substrate, high processability and low cost.