| Abstract
| - Alkanethiols HS(CH2)nCH3 (n = 7, 11, 15, 17) and the hydroxy functional thiol HS(CH2)12OH are shownto adsorb from solution onto zinc selenide crystals and form well-organized monolayers. The chemisorptionof these organosulfur compounds has been studied using transmission Fourier transform infraredspectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and surfacewetting properties. FTIR indicates that the longer chain alkanethiols (n = 15, 17) form well-defined SAMswith crystalline-like conformations of the chains within the monolayers. As the chain length decreases,there is less conformational order present in the monolayers. The orientation of the largely trans-zigzagalkyl chains on the surface is at a slight tilt off the surface normal direction, as indicated by the dichroismof the infrared spectra and the chain-length-dependent scaling of the mass coverage of the SAM. Thestructural data obtained by XPS and FTIR are compatible with the inferences derived from measurementsof surface wetting properties. The thickness of the SAM layers calculated using XPS is found to be comparableto the thickness of alkanethiol SAMs formed on gold and other metal surfaces. Changes in the surface ofthe ZnSe crystal because of chemisorption of the thiols are illustrated by data from AFM imaging. Thefeasibility of forming cohesive patterned monolayers by microcontact printing is also demonstrated.
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