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

This paper outlines a general synthetic route to alkanethiols useful i n 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 measur ed by ellipsometry and X-ray photoelectron spectroscopy, XPS) of SAMs having an amide moiety beta to Au/thiolate were similar to those of SA Ms of alkanethiols with similar backbone length on gold. The internal amide group present in SAMs prepared from CF3CH2-NHCOCH2SH increases t heir stability against desorption or exchange with hexadecanethiol in ethanol relative to SAMs from CF3(CH2)(3)SH. The desorption of SAMs fr om 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 c ontrast, showed no loss after 48 h at similar to 10(-9) Torr. The rate of exchange of a SAM from CF3CH2NKCOCH2SH with hexadecanethiol in eth anol 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 C F3CH2NHCOCH2SH, followed by protection of the UV-damaged SAM by replac ement with hexadecanethiol and etching, gave gold patterns with minimu m feature sizes of 5 mu m; these sizes were limited by the lithographi c procedure used and do not reflect the true edge resolution of this p hotolithographic method.