Plasma pretreatments are environmentally benign and energy-efficient processes for modifying the surface chemistry of materials. This study was undertaken to better understand the chemical and physical properties of plasma-polymerized (PP) acetylene films, and the adhesion of PP films to titanium and silicon substrates. The composition, mechanical properties, and adhesion of PP acetylene films have been investigated with X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and nanoindentation and nanoscratch atomic force microscopy (AFM). Thin PP films prepared from acetylene were deposited onto polished Ti-6Al-4V and silicon wafers with a low pressure, radio frequency, inductively coupled plasma reactor. Relationships between composition, mechanical properties, and adhesion of PP films on Ti-6Al-4V and silicon wafers were investigated.
Deposited PP acetylene films were predominantly carbon (E87%). Oxygen, the other main constituent (E13%), was present in the form of C-O and CQO functional groups. For both substrates, PP films deposited at lower power exhibited higher hardness and reduced modulus than films deposited at higher power. At two different power levels, PP films deposited on silicon wafers exhibited higher hardness and reduced modulus values than PP films deposited on polished Ti-6Al-4V. Also, film deposition occurred at a faster rate on Ti-6Al-4V. Overall, thinner films exhibited higher hardness and a greater reduced Young's modulus compared to thicker films. For the samples tested, PP films of higher hardness yielded higher critical loads at debond (thickness normalized) in nanoscratch tests.