Molecularly Resolved Surface Superstructures of Self-Assembled Butanethiol Monolayers on Gold

Abstract

Self-assembled monolayers of butanethiol adsorbed onto highly uniform Au/mica films have been studied using in-air scanning tunneling microscopy (STM) and infrared spectroscopy. STM images taken of fully equilibrated films show molecularly resolved features that are believed to correspond to the methyl terminations of the organic surface. Large domains of organized adsorbates and a variant of the previously reported p× 3 superlattice structure are observed on these surfaces; using this nomenclature, the basic repeat unit of the structure reported herein corresponds to 7× 3. Lateral variations in the elevations of striped structures are tentatively assigned to thiolates bound into fcc sites of the Au(111) substrate. We have also observed molecular structure in regions of the superlattice that were structureless in UHV-STM studies. These observations suggest that the filling factor of the fully equilibrated surfaces is highly sensitive to the manner of sample preparation and storage. Large-scale desorption of thiolates does not appear to be a necessary step in the formation of highly organized films of these short-chain systems when equilibrated in thiol/methanol solutions, and the sample processing history may have significant effects on the ultimate surface topology.

Adlayer structures of dl-homocysteine and l-homocysteine thiolactone on Au(1 1 1) surface: an in situ STM study

“…5c is 47 • . The brightness difference between the two S atoms can be due to the different adsorption sites, which has been reported previously [18][19][20][21]. The bright spot in STM image corresponds to the S atom in fcc position and the dark one in hcp position.…”

Scanning Tunneling Spectroscopy of Insulating Self-Assembled Monolayers on Au(111)

“…One concern with the experimental conditions reported here is that a strong electric field can polarize molecular orbitals, effectively decreasing η below 0.5 at the threshold voltage bias. 28 Previous STM studies [17][18][19][20][21][22][23][24][25]27 of molecules adsorbed onto Au substrates have employed relatively small tunnel currents (3-30 pA) with subsequently low voltage requirements (|V bias | < 1.2 V). However, the molecules in this study have relatively low polarizabilities because of their high volume fraction of saturated hydrocarbon so their electronic structures should not be strongly perturbed at high fields, although they may induce some nonlinearities (see above).…”

“…We have applied this method toward measuring the electrical conductances of SAMs prepared from dodecanethiol (DDT), octadecanethiol (ODT), and resorcinarene C10 tetrasulfide (RC10TS) on Au(111) (see Figure 1). The structure and electrochemically insulative properties of these well-ordered monolayers have been characterized by a number of experimental methods including STM, [17][18][19][20][21][22][23][24][25]27,35 and their differences in thickness or chemical bonding to Au make them ideal substrates for evaluating this approach.…”

n-alkyl thiol head-group interactions with the Au(111) surface

“…[9][10][11][12][24][25][26] Furthermore, other structural models have been reported, including n × √ 3 unit cells (8 ≤ n ≤ 10). [36][37][38][39] There is even controversy among proponents of the sulfur pairing model, with some researchers suggesting top and hollow-bridge positions for the sulfurs, while others propose a hollow and hollow-bridge dimer.…”