TY - JOUR
T1 - In situ studies of thiol self-assembly on gold from solution using atomic force microscopy
AU - Xu, Song
AU - Cruchon-Dupeyrat, Sylvain J N
AU - Garno, Jayne C.
AU - Liu, Gang-yu
AU - Jennings, G. Kane
AU - Yong, Tseh Hwan
AU - Laibinis, Paul E.
PY - 1998/3/22
Y1 - 1998/3/22
N2 - The kinetics and mechanism for the solution-phase adsorption of n-alkanethiols onto gold to form self-assembled monolayers (SAMs) have been monitored in situ using atomic force microscopy (AFM). Time-dependent AFM images reveal detailed structural information about the adsorbed layer during its growth. In 2-butanol, CH3(CH2)17SH molecules initially adsorb on gold with the molecular axis of their hydrocarbon chains oriented parallel to the surface. As the surface coverage increases to near saturation, a two-dimensional phase transition occurs and produces islands composed of molecules with their hydrocarbon axis oriented ∼30° from the surface normal. Continued exposure to the thiol solution results in a greater number of these islands and the growth of these nuclei until a SAM is formed with a commensurate (√3 × √3)R30° structure. The growth of the lying-down phase follows a first-order Langmuir adsorption isotherm, while the phase transition is best described by a second-order reaction. The kinetics of the self-assembly process also depends on the chain length of the alkanethiol and the cleanness of the gold surface. Longer-chained thiols, such as CH3(CH2)17O(CH2)19SH, formed complete SAMs more rapidly than did shorter-chained thiols, such as CH3(CH2)17SH. The physisorbed, lying-down phase for CH3(CH2)17O(CH2)19SH was less homogeneous and its two-dimensional phase transition was more complicated than for CH3(CH2)17SH and CH3(CH2)21SH, as the CH3(CH2)17O(CH2)19SH molecules adopt multiple conformations. Of these, the two dominant ones are an all-trans, and another where the hydrocarbon chain adopts an all-trans conformation except for a gauche bond on both sides of the ether unit. These conformers coexist on the surface during the initial adsorption and its transition to the standing-up phase, but change to the all-trans structure in the complete SAM.
AB - The kinetics and mechanism for the solution-phase adsorption of n-alkanethiols onto gold to form self-assembled monolayers (SAMs) have been monitored in situ using atomic force microscopy (AFM). Time-dependent AFM images reveal detailed structural information about the adsorbed layer during its growth. In 2-butanol, CH3(CH2)17SH molecules initially adsorb on gold with the molecular axis of their hydrocarbon chains oriented parallel to the surface. As the surface coverage increases to near saturation, a two-dimensional phase transition occurs and produces islands composed of molecules with their hydrocarbon axis oriented ∼30° from the surface normal. Continued exposure to the thiol solution results in a greater number of these islands and the growth of these nuclei until a SAM is formed with a commensurate (√3 × √3)R30° structure. The growth of the lying-down phase follows a first-order Langmuir adsorption isotherm, while the phase transition is best described by a second-order reaction. The kinetics of the self-assembly process also depends on the chain length of the alkanethiol and the cleanness of the gold surface. Longer-chained thiols, such as CH3(CH2)17O(CH2)19SH, formed complete SAMs more rapidly than did shorter-chained thiols, such as CH3(CH2)17SH. The physisorbed, lying-down phase for CH3(CH2)17O(CH2)19SH was less homogeneous and its two-dimensional phase transition was more complicated than for CH3(CH2)17SH and CH3(CH2)21SH, as the CH3(CH2)17O(CH2)19SH molecules adopt multiple conformations. Of these, the two dominant ones are an all-trans, and another where the hydrocarbon chain adopts an all-trans conformation except for a gauche bond on both sides of the ether unit. These conformers coexist on the surface during the initial adsorption and its transition to the standing-up phase, but change to the all-trans structure in the complete SAM.
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M3 - Article
AN - SCOPUS:0032023781
VL - 108
SP - 5002
EP - 5012
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 12
ER -