n-Alkanethiol (C n H2n+1SH) self-assembled monolayers (SAMs) adsorbed on Au(111) were studied with an atomic force microscope (AFM) to confirm the influence of the lateral interaction between adsorbed thiols on the film morphology. Two experiments were performed:  firstly, a study of the domain formation at the initial stage of SAM growth (single component) and, secondly, investigations of the coadsorption phenomenon in mixed SAMs composed of two alkanethiols having different chain lengths. For the kinetics study, Au(111) was immersed into the 10-2 mM ethanol solutions with the single component alkanethiol (C4H9SH, C12H25SH, or C18H37SH), for varying times (1 s to 10 min). In all cases, the film coverage increased as the immersion time became longer, and finally the surface was totally covered with thiols after an immersion time of 3 min or more. Clear island formations were observed in the partially covered C12H25SH and C18H37SH SAMs, while C4H9SH formed meshlike domains. The mixed SAMs were prepared by immersing Au(111) into 1 mM ethanol solutions with mixed alkanethiols (C4H9SH/C18H37SH) of various compositions, R soln = [C4H9SH]/[C18H37SH] = 1/1 to 100/1, for a time of 1 h. Clear phase separation was observed at R soln = 20/1 and 40/1. Above or below these compositions, the film surface appeared very flat, covered with a nearly single component, C4H9SH or C18H37SH, respectively. This is the first systematic study of the surface phase behavior of alkanethiol SAMs by AFM imaging. It reveals more direct information about the film morphology than previous studies with conventional surface analytical techniques such as X-ray photoelectron spectroscopy, ellipsometry, contact angles, etc.

Self‐assembled monolayers (SAMs) formed from semifluorinated alkanethiols (SFATs) CF3(CF2)9(CH2)nSH (F10HnSH: n = 2, 11, and 17) on poly‐crystalline Au and Ag were characterized by X‐ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and near edge X‐ray absorption fine structure spectroscopy. SFATs were found to form highly ordered and densely packed SAMs on both substrates. The molecules are strongly bonded to the substrates via their sulfur head groups, in the same manner as conventional alkanethiol (AT) SAMs. The hydrocarbon (except for n = 2) and fluorocarbon parts of the adsorbed SFATs retain the expected planar zigzag and helical conformations of the respective bulk materials. The orientation of the fluorocarbon chains does not depend on the substrate. These entities are almost perpendicular to the substrate in F10H2S/Au and F10H2S/Ag and become slightly more tilted in SFAT SAMs with longer hydrocarbon moieties. However, the alkyl parts of the SFAT films exhibit tilt and twist angles that are similar to those of normal alkanethiol films on Ag and Au substrates despite the reduced packing density in the SFAT films as compared to normal AT SAMs. We suggest that the substrate‐related differences in tilt and twist angles for both systems are associated with the different character of the head‐group‐substrate bonding on Au and Ag.

The microstructure, wettability, and thermal stability of self-assembled monolayers (SAMs) on gold generated from semifluorinated alkanethiols F(CF2)10(CH2) n SH, where n = 2, 6, 11, 17, and 33 (F10HnSH), were examined by polarization modulation infrared reflection absoprtion spectroscopy (PM-IRRAS) and dynamic contact angle measurements. Analysis by PM-IRRAS revealed that the length of the methylene spacer (Hn) influenced the tilt angle of the fluorocarbon segments in the semifluorinated SAMs. As the length of the methylene spacer was increased, the tilt angle of the perfluorocarbon moiety increased with respect to the surface normal. The longer methylene spacers (Hn, n = 11, 17, and 33) exhibited well-ordered trans-extended conformations as indicated by the position of the antisymmetric methylene band (νa CH 2 = 2919 cm-1). Shortening the length of the methylene spacer to n = 6, however, led to a decrease in conformational order (νa CH 2 = 2925 cm-1). Dynamic contact angle measurements using the Wilhelmy plate method showed that the semifluorinated SAMs were poorly wet by both water (average θa = 120°) and hexadecane (average θa = 81°). The wettability varied with the length of the methylene spacer; in particular, both the thinnest and the thickest semifluorinated SAMs (derived from F10H2SH and F10H33SH, respectively) exhibited relatively low dynamic contact angle values. In addition, the thermal stability of the semifluorinated SAMs was found to increase as the length of the methylene spacer was increased. Overall, these films exhibited remarkable resistance to thermal degradation (e.g., SAMs derived from F10H33SH sustained a relatively high contact angles after incubation at 150 °C for 1 h in air).

The structures of semifluorinated alkanethiol self-assembled monolayers (SAMs) generated by the adsorption of CF3(CF2)9(CH2)nSH (F10HnSH, n ) 2, 6, 11, 17, 33) onto gold were investigated with atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and surface plasmon resonance spectroscopy. Images obtained by AFM of the F10H2SH SAM showed a remarkably ordered 2D hexagonal lattice with a lattice constant, a ) 5.9 ( 0.1 Å, on Au(111)/mica. As the total number of carbon atoms in the alkyl spacer groups (n) was increased, the fluorocarbon adlayer structure appeared more disordered in the AFM images; however, the thicknesses of the fluorocarbon layers estimated from the C 1s (CF3), C 1s (CF2), and F 1s XPS signal intensities were indistinguishable in all of the SAMs. In contrast, the C 1s (CH2) signals revealed that the tilt angles of the alkyl spacer groups depended strongly on n. We utilized a contrast variation SPR technique with various contacting media for an independent determination of the refractive indices and the film thicknesses of the semifluorinated SAMs. The obtained data were consistent with our AFM and XPS results, which show that the longer alkyl chains pack more densely than the shorter ones in these SAMs.