Electrically Conductive Thin Films Prepared from Layer-by-Layer Assembly of Graphite Platelets

Layer-by-layer (LBL) assembly of carbon nanoparticles for low electrical contact resistance thin film applications is demonstrated. The nanoparticles consist of irregularly shaped graphite platelets, with acrylamide/beta-methacryl-oxyethyl-trimethyl-ammonium copolymer as the cationic binder. Nanoparticle zeta (zeta) potential and thereby electrostatic interactions are varied by altering the pH of graphite suspension as well as that of the binder suspension. Film thickness as a function of zeta potential, immersion time, and the number of layers deposited is obtained using Monte Carlo simulation of the energy dispersive spectroscopy measurements. Multilayer film surface morphology is visualized via field-emission scanning electron microscopy and atomic-force microscopy. Thin film electrical properties are characterized using electrical contact resistance measurements. Graphite nanoparticles are found to self-assemble onto gold substrates through two distinct yet overlapping mechanisms. The first mechanism is characterized by logarithmic carbon uptake with respect to the number of deposition cycles and slow clustering of nanoparticles; on the gold surface. The second mechanism results from more rapid LBL nanoparticle assembly and is characterized by linear weight uptake with respect to the number of deposition cycles and a constant bilayer thickness of 15 to 21 rim. Thin-film electrical contact resistance is found to be proportional to the thickness after equilibration of the bilayer structure. Measured values range from 1.6 m Omega cm(-2) at 173 nm to 3.5 m Omega cm(-2) at 276 rim. Coating volume resistivity is reduced when electrostatic interactions are enhanced during LBL assembly.