Mh. Hu et al., Structure and morphology of self-assembled 3-mercaptopropyltrimethoxysilane layers on silicon oxide, APPL SURF S, 181(3-4), 2001, pp. 307-316
Self-assembled 3-mereaptopropyltrimethoxysilane (MPTMS, (CH3O)(3)SiCH2CH2CH
2SH) layers on hydroxyl-terminated silicon oxide (SiO2) were prepared at MP
TMS concentrations ranging from 5 x 10(-3) to 4 x 10(-2) M. The surface str
ucture and morphology of MPTMS layers were characterized by X-ray photoelec
tron spectroscopy (XPS), contact angle measurements, scanning electron micr
oscopy (SEM), and atomic force microscopy (AFM). We found that the MPTMS la
yers on SiO2 consisted of dispersed domains 20-200 run in diameter, instead
of continuous, flat monolayers. With increasing MPTMS concentration, the d
omain shape changed from flat to steep. Flat domains were composed of well-
ordered monolayers with thiol headgroups uniformly distributed on the upper
most surface, whereas steep domains were composed of disordered polymers wi
th randomly distributed thiol headgroups on the uppermost surface. These re
sults indicate that MPTMS molecules show good self-assembly at an MPTMS con
centration of 5 x 10(-3) M, but not above this concentration. The effect of
MPTMS concentration on the structure and morphology of MPTMS layers might
be due to the competition between self-polymerization and surface dehydrati
on reactions, which depends on the trace quantity of water in the solvent a
nd on the SiO2 surface. Our research further indicates that MPTMS and water
concentrations are the controlling parameters for preparing well-ordered,
self-assembled MPTMS monolayers on SiO2. (C) 2001 Elsevier Science B.V All
rights reserved.