INDUCED ORIENTATIONAL ORDER IN LONG ALKYL CHAIN AMINOSILANE MOLECULESBY PREADSORBED OCTADECYLTRICHLOROSILANE ON HYDROXYLATED SI(100)

We studied the adsorption of (17-aminoheptadecyl)trimethoxysilane (AHT MS; NH2(CH2)(17)Si(OCH3)(3)) onto hydroxylated Si(100) wafers, which w ere preexposed to methyl-terminated n-octadecyltrichlorosilane (OTS; C H3(CH2)(17)SiCl3) for various immersion periods, resulting in partial coverages between 42% and 88% of a complete monolayer. Preadsorption o f a partial monolayer of OTS was found to drastically improve the mole cular alignment of subsequently adsorbed AHTMS. This effect was observ ed for submonolayer OTS films exhibiting both an island or a homogeneo us growth mode, as determined by atomic force microscopy. Without prea dsorbed OTS, the adsorption of AHTMS from an aged solution typically r esulted in films of multilayer thickness, while the use of fresh solut ions of AHTMS resulted in disordered films of submonolayer coverage. W e suggest that submonolayer quantities of preadsorbed OTS prevent, coa gulated aminosilane adsorption and enable oriented adsorption of amino silane molecules along the domain perimeter of aligned and ordered met hyl-terminated silane. In comparison to sequential adsorption, coadsor ption of n-octadecyltrimethoxysilane (OTMS; CH3(CH2)(17)Si(OCH3)(3)) w ith AHTMS from a mixture gave films of low quality. The OTS/AHTMS surf ace that was prepared by sequential adsorption was exposed to pentaflu orobenzaldehyde (PFBA) to probe the reactivity and orientation of the AHTMS amino groups. Eighteen to thirty-four percent of the amine group s reacted with no or minor disturbance to the molecular order, compare d to 21-44% on pure and disordered AHTMS multilayers. This indicates t hat the coupling reaction with PFBA in toluene involves only part of t he amino groups at the interface.