Growth and analysis of octadecylsiloxane monolayers on Al2O3 (0001).
On solvent-cleaned and piranha-etched single-crystal Al2O3(0001) surfaces, uniform, robust, self-assembled monolayers of octadecylsiloxane (ODS) are formed by 48 h exposure to a solution containing octadecyltrichlorosilane (OTS) in an anhydrous atmosphere. X-ray photoelectron spectroscopy, atomic force microscopy, ellipsometry, and water contact angle measurements confirm the presence of a uniform, complete monolayer. Reducing the exposure time or omitting the piranha-etch leads to much less uniform coverage. The ODS monolayers are stable when stored in ambient atmospheres for month-long periods. Thermal desorption in a vacuum environment (10(-9) Torr) shows the ODS monolayer is thermally stable up to at least 420 K. When heated in 200 mTorr of flowing forming gas (N2-10% H2) for 1 h at 520 K, slow loss of ODS was indicated. A schematic model is proposed which involves island nucleation by covalent bonding of OTS to surface hydroxyl groups followed by growth through the addition of mobile ODS species.
Mitchon
Lauren N
LN
Department of Chemistry and Biochemistry, Center for Materials Chemistry, University of Texas at Austin, Austin, TX 78712, USA.
White
J M
JM
D000537:Aluminum Oxide / Q000737:chemistry*; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force / Q000379:methods; D012680:Sensitivity and Specificity; D012833:Siloxanes / Q000737:chemistry*; D013053:Spectrophotometry / Q000379:methods; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry; D014965:X-Rays
D008567:Membranes, Artificial; D012833:Siloxanes; D014867:Water; D000537:Aluminum Oxide