SELF-ASSEMBLED MONOLAYERS ON GOLD GENERATED FROM ALKANETHIOLS WITH THE STRUCTURE RNHCOCH(2)SH

This paper outlines a general synthetic route to alkanethiols useful in forming self-assembled monolayers (SAMs) starting from amines, RNH(2), and converting them, via alpha-chloroamides RNHCOCH(2)Cl, to thiols having the structure RNHCOCH(2)SH. The wettabilities (estimated from contact angles of water and hexadecane) and the thicknesses (as measured by ellipsometry and X-ray photoelectron spectroscopy, XPS) of SAMs having an amide moiety beta to Au/thiolate were similar to those of SAMs of alkanethiols with similar backbone length on gold. The internal amide group present in SAMs prepared from CF3CH2-NHCOCH2SH increases their stability against desorption or exchange with hexadecanethiol in ethanol relative to SAMs from CF3(CH2)(3)SH. The desorption of SAMs from CF3(CK2)(3)SH was first order in the alkanethiolate and had a half-life of similar to 2 h at 10(-9) Torr; SAMs from CF3CH2NHCOCH2SH, by contrast, showed no loss after 48 h at similar to 10(-9) Torr. The rate of exchange of a SAM from CF3CH2NKCOCH2SH with hexadecanethiol in ethanol was 10(2)-10(3) times slower than the SAMs from CH3(CH2)(3)SH or from CF3(CH2)(3)-SH. The susceptibility of a SAM prepared from a short-chain alkanethiol (e.g., CH3(CH2)(3)SH or CF3CH2NHCOCH2SH) to damage by UV was 10 times greater than that observed for a SAM prepared from hexadecanethiol (as measured by XPS). UV damage of SAMs derived from CF3CH2NHCOCH2SH, followed by protection of the UV-damaged SAM by replacement with hexadecanethiol and etching, gave gold patterns with minimum feature sizes of 5 mu m; these sizes were limited by the lithographic procedure used and do not reflect the true edge resolution of this photolithographic method.