Microscale chemical and electrostatic surface patterning of Dow Cyclotene by N 2 plasma

Abstract

Using TEM grids as masks, we have chemically modified selected areas of the surface of Dow Cyclotene, a low permittivity polymer, by a N 2 plasma (chemical surface patterning), grafting a maximum of ∼3% N; this was verified by XPS (X-ray photoelectron spectroscopy) and TOF-S-SIMS (time-of-flight static secondary ion mass spectrometry) chemical imaging. Contact mode AFM (atomic force microscopy) studies of the modified surface morphology show unexpected, initially large, values of both etch depth and friction in the treated areas, which decrease on exposure to atmosphere; similar results were absent in tapping mode images. When Cu, which forms nanoclusters on Cyclotene, was deposited by evaporation onto freshly etched Cyclotene, the large etch depth and friction in the etched areas decreased to much lower values. The depth and friction differences occurring on surface modification, which were revealed through our use of patterning, are apparent, and are, in fact, caused by enhanced electrostatic interaction of the chemically modified surface with the AFM tip, as confirmed by the tapping mode data. Some of the electrostatic surface charge, introduced by the positively charged species chemically modifying the Cyclotene surface, is reduced by subsequent charge neutralization. XPS has shown this to be due to the oxidation of these surface charges on atmospheric exposure, initially ∼70%, to form alcohol, carbonyl and carboxylic acid groups. Contact mode AFM imaging of plasma-patterned surfaces is revealed as an excellent tool for the high-resolution characterization of such surfaces.