Langmuir, Vol.10, No.4, 984-987, 1994
Packing of Hydrocarbon and Perfluorocarbon Chains Planted on Oxidized Surface of Silicon as Studied by Ellipsometry and Atomic-Force Microscopy
The oxidized surface of a single crystal of silicon was silylized with octadecyltrichlorosilane (OTS), perfluorooctylmethyldichlorosilane (FOMDS), or perfluorodecyltrichlorosilane (FDTS) to give a hydrophobic surface that shows a contact angle larger than 110-degrees to water. The optimal condition of silylation was established to give a well-qualified hydrophobic surface. Both the thickness and the refractive index of the oxide and the alkylated layers grown on silicon surface were measured by ellipsometry. Each octadecyl chain was found to occupy 0.6 +/- 0.1 nm2 of silicon surface and to have an orientation slightly slanted to the surface normal. The hydrophobic surfaces obtained were also examined in water by atomic force microscopy. The atomic force micrograph shows that the alkyl chains of OTS, FOMDS, or FDTS are oriented at the surface to give an occupied area of 0.43 +/- 0.07, 0.52 +/- 0.07, or 0.50 +/- 0.08 nm2, respectively. The occupied area of fluorocarbon chain was found 15% larger than that of hydrocarbon chain.