Scanning tunneling microscopy and atomic-force microscopy of n-alkanethiolate monolayers spontaneously adsorbed at gold surfaces

摘要

Monolayer films of alkanethiolates CH$-3$/(CH$-2$/)$-n$/SH at Au(111) films on mica were examined by scanning tunneling microscopy (STM) (n $EQ 1,9,17) and AFM (n $EQ 1 - 17). The resulting atomically resolved images reveal the packing arrangement of the overlayer. Observed images correspond to a hexagonally packed array of adsorbates with respective nearest- and next-nearest-neighbor spacings of 0.50 $POM 0.02 nm and 0.87 $POM 0.04 nm with STM and 0.52 $POM 0.03 nm and 0.90 $POM 0.04 nm with the AFM. This packing agrees with the expected ($ROOT@3 $MUL $ROOT@3)R30$DGR adlayer structure of the adsorbate. We believe the STM images reflect the arrangement near the gold-bound sulfur interface, whereas the AFM images reveal the arrangement of the alkyl chains.