The effect of ion energy on the chemistry of air-aged polymer films grown from the hyperthermal polyatomic ion Si2OMe5+

Thin polymer films have been grown from hyperthermal [m/z 147, Si2OMe5+] ions, using ion energies of 15, 25, 50, and 100 eV. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) analyses were undertaken of the air-aged polymer films. The SMS and XPS of samples deposited from ion beams of 15 and 25 eV energies (15 and 25 eV polymers) are remarkably similar, but different in a number of respects to those of the 50 and 100 eV polymers. The positive SMS of the lower energy polymers resemble closely that of the linear polymer polydimethyl siloxane (PDMS). However, the XPS of these polymers reveal a range of silicon binding environments [Si-C/H, Si(-O-1) Si(-O-2) (Si-O-3) and Si(-O-4)], whilst the 'monomer ion' (m/z 147) has only one, Si(-O-1). Although the positive ion SIMS of the 50 and 100 eV polymers contain 'PDMS-like' fragments (m/z 147, 207, 221, 281), these ions are much reduced in intensity (cf. 15 and 25 eV), and we postulate that the extent of cross-linking is much higher in these polymers. In fitting the XPS of these polymers it was necessary to include an additional component peak for Si(-Si-3). These polymers are compared with a low power plasma polymer of HMDSO. The polymers grown from the 15 and 25 eV ions are remarkably similar to the plasma polymer in terms of their molecular structure and their surface chemistry. (C) 2001 Elsevier Science BY All rights reserved.