Surface Morphology in the Early Stages of Plasma Polymer Film Growth from Amine-Containing Monomers

The manner by which plasma polymers grow in the very first stages of deposition is a topic which has been almost overlooked. We show using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) that in the early stages of plasma deposition there are significant differences in the way plasma polymers grow from two amine-containing compounds onto silicon wafers. By AFM it is shown that films grown from n-heptylamine (HA) initially show 'island-like' growth before a continuous smooth film is formed. In contrast, films from allylamine grow smoothly from the very earliest stages. XPS data show substantial differences of plasma polymer chemistry in close proximity to the silicon surface manifested in the formation of NH⁺₃ and NO_x species which are more abundant in films of HA. We present a possible explanation for these results based upon post-plasma surface phenomena in the case of HA. In this communication we show that in the early stages of plasma deposition there are significant morphological and chemical differences in the way plasma polymers grow from two amine-containing compounds onto silicon wafers. Films grown from n-heptylamine initially show 'island-like' growth before a continuous smooth film is formed. In contrast, films from allylamine grow smoothly from the very earliest stages. We provide a possible explanation of these findings.