Monolayer films formed by the chemisorption of alkanethiols (CH,(CH2)^SH, n = 1-17) at epitaxially grown Au(l 11) films were examined using atomic force microscopy (AFM). Atomically resolved images were found for films with n > 4, directly revealing for the first time the arrangement of the alkyl chain structure. All of the images exhibit a periodic hexagonal pattern of equivalent spacings (e.g., respective nearest-and next-nearest-neighbor distances of 0.52 ± 0.03 and 0.90 ± 0.04 nm for n = 17 and 0.51 ± 0.02 and 0.92 ± 0.06 nm for n = 5). These spacings agree well with the analogous 0.50and 0.87-nm distances of a (V3 X v/3)R30°adlayer on a Au(l 11) lattice, the two-dimensional arrangement reported in recent diffraction1 2"3 and scanning tunneling microscopy4,5 studies. In some instances, images with the above spacings were observed to extend continuously over areas as large as 100 nm2 *, suggesting the potential of AFM to reveal both the shortand long-range order of the alkyl chains of these and other model interfacial structures. The implications of these findings, including the inability to obtain well-resolved images for films with n < 3, are examined in the context both of the current structural descriptions of alkanethiolate monolayers and of general issues related to imaging organic films with AFM.

This paper describes the preparation and characterization of interfacial structures formed by the deposition of thin (~0.2 and 5 nm) overlayer Alms of Cu at carboxylic acid-terminated thiolate monolayers adsorbed at Au. Infrared reAection spectroscopy (IRS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) have been used to probe both compositional and structural details of the interfaces. The monolayers are formed by the chemisorption of carboxylic acid-terminated alkanethiols (H02C-(CH2)"SH, n = 10 and 15) from dilute ethanolic solutions at the surface of evaporated Au Alms. Prior to Cu deposition, the IRS data indicate that the polymethylene chains form a densely packed surface phase for n = 15 and a more disordered surface phase for n = 10. For n = 10 and n = 15, the terminal carboxylic acids exist in both free and hydrogen-bonded forms. Deposition of a Cu overlayer by resistive evaporation and subsequent exposure to the laboratory ambient leads to the formation of a carboxylate salt as revealed by the detection of both the va(COO-) and ps(COO~) modes by IRS. The IRS data also show that Cu deposition induces disorder in the underlying polymethylene chain structure relative to that of the uncoated monolayer. Both the XPS and IRS data reveal that Cu is bound in its +2 oxidation state to the carboxylate.Images from AFM indicate that the crystallite size (~20 nm) of the Cu overlayer is markedly less than that (~200-300 nm) of anchoring metal substrate. The potential application of this adsorbate-substrate system to fundamental studies of the adhesion of metal overlayers at surface functionalized polymeric materials is brieAy discussed.

This paper presents the results of an infrared spectroscopic and wettability examination of monolayers formed by the spontaneous adsorption of short chain n-alkanoic acids ( C H~( C H Z )~C O O H , n = 0-9) from the gas phase onto Ag. The infrared spectral data, collected in an external reflection mode, indicate that the monolayers chemisorb as the corresponding salt and that the chains contain all-trans conformational sequences for n = 1-9. The chemisorption process is further exemplified by the formation of a carboxylate group that is symmetrically bound at Ag as either a bidentate or bridging ligand. The conformational insights are developed on the basis of an unusually prominent series of the methylene wagging progression. An in-depth analysis resulted in the complete assignment of the fundamental modes in the progression as well as a reassignment of the C C stretch in the region of this progression. Structural insights developed from the infrared spectral data and contact angle measurements are compared to analogous monolayers formed from dilute solution. This comparison points to the subtle, but important, role of solvent in influencing the structure of the monolayer.

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