ATOMIC-FORCE MICROSCOPIC CHARACTERIZATION OF A FLUORINATED ALKANETHIOLATE MONOLAYER AT GOLD AND CORRELATIONS TO ELECTROCHEMICAL AND INFRARED REFLECTION SPECTROSCOPIC STRUCTURAL DESCRIPTIONS

Monolayers formed by the chemisorption of CF3(CF2)7(CH2)2SH (FT) at epitaxially grown Au(lll) films were characterized using atomic force microscopy (AFM), electrochemistry, and infrared reflection spectroscopy (IRS). The AFM was used to probe the atomic scale arrangement of the monolayer. The electrochemical and IRS studies provided insight into the surface coverage and spatial orientation of the monolayer. The AFM images exhibit ordered domains of hexagonal periodicity with average nearest- and next-nearest-neighbor separation distances of 0.58+/-0.02 and 1.01+/-0.02 nm, respectively. These spacings agree well with a (2 x 2) adlayer at Au(lll), a two-dimensional arrangement predicted on the basis of considerations of a space-filling model. The sizes of the ordered domains typically range from a few adsorbates up to 30 nm2 and occasionally larger. The results of the surface coverage ((5.7+/-0.7) X 10(10) mol/cm2) and orientational analysis (20-degrees average tilt of the perfluorocarbon chains from the surface normal) support the presence of a (2 X 2) adlayer. Differences in the ability to image the FT monolayer and those formed from alkanethiols (CH3(CH2)nSH) are discussed, along with the advantages of correlating the findings from microscopic and macroscopic characterization techniques.