Scanning Probe Microscopy Depth Measurements of Self-Assembled Monolayer Structures on Gold

Abstract

Scanmng tunneling microscopy (STM) images of a self-assembled alkanethiol monolayer film on gold show a structure that contains flat areas with pits. An important characteristic of these pits, and one which has been a subject of interest in the recent literature, is their depth. For instances in which the measured depth is comparable to a single atomic step height of the gold substrate, the pits have been assigned as monolayer-deep defects in the gold substrate, covered by alkanethiol molecules. For instances in which the measured depth is greater than a single atomic step height ofgold, the pita have been assigned as defects in the alkanethiol monolayer itself. Since the diameters of those pits are small and the tips used for " h g probe microscopy (SPM) imaging have a finite radius, it is possible that the structural interaction between the tip and surface prevents SPM from measuring the true depth of the pits in most cases. In this study, we construct a model to understand this phenomenon quantitatively, and analyze the measured depth of the pita. STM images of self-assembled octadecanethioVAu(ll1) from the same surface but obtained with tips of Merent sizes are presented. We show that in some STM images the apparent depth of the pits is coincidently comparable with the single atomic step height of the gold substrate surface. In other images we show that the true depth of the pit is measured, and that it is interpreted as the thickness of an odadecanethiol monolayer (-25.3 f 0.5 A).

Surface Structure of Binary Self-Assembled Monolayers Formed by Electrochemical Selective Replacement of Adsorbed Thiols

“…10 The measured height difference depends on the condition of the tip and usually the height from STM images of thiol SAMs tends to be smaller than the actual value. 13,22 The area of the brighter domains increased as the ratio of MPA increased in the starting system (Figure 4, a and b), suggesting that the brighter domains mainly consist of HDT molecules. The STM image of Figure 4c shows ( 3 × 3)R30°structure of thiol molecules on the brighter domains (shown by arrows).…”

The Chemistry of Self-Assembled Long-Chain Alkanethiol Monolayers on Gold

“…The Surface Analysis Techniques pits can be removed by heating the surface without damage Low-energy electron diffraction can be used to determine to the CH 3 (CH 2 ) n SH/Au(111) monolayer. The depth of the the monolayer structure and registry on the substrate, howpits were measured by Beebe et al using STM (73). The ever, single crystalline substrates are usually required (82).…”

Characterization of Organosulfur Molecular Monolayers on Au(111) using Scanning Tunneling Microscopy

“…AuC n X has been studied using a plethora of analytical techniques and has been at least twice reviewed. , Of the techniques employed, scanning tunneling microscopy (STM) is unique in its ability to characterize structure, nondestructively, in direct space, and with routine single-molecule or single-atom resolution. , This review will not address all experimental and theoretical analyses, only those that employed STM to study AuC n X. − ...…”