Adsorption, Assembly, and Dynamics of Dibutyl Sulfide on Au{111}

Abstract

Alkanethiol (RSH) monolayers are by far the most extensively studied surface self-assembly systems due to their robustness and the opportunity to control their assembly in the dimension perpendicular to the surface. Thioethers (RSR′), a similar class of molecule, remain largely unstudied to date but may offer a similar level of assembly control parallel to the surface. Here we report the self-assembly of dibutyl sulfide, a symmetric thioether species, on a Au{111} surface using scanning tunneling microscopy. As with thiols, dibutyl sulfide forms well-ordered monolayers, but due to the slightly weaker molecule-metal bond, the coverage and temperature-dependent behavior is very different than that of alkanethiols. Adsorption is sensitive to the different regions of the Au{111} herringbone reconstruction. Dibutyl sulfide lies parallel to the surface and forms well-ordered chains in domains that preferentially bind first in fcc regions, then hcp, and finally on soliton walls. The sulfide-Au interaction is strong enough to disrupt the native herringbone reconstruction of Au; however, unlike thiols, dibutyl sulfide adsorption does not result in etch pit formation. A monolayer of dibutyl sulfide has a very low defect density as compared to thiol-SAM based systems. This low defect density hints at the possibility of using a thioether moiety as a basis for a self-assembled system free of typical defects like etch pits, which allow attack and degradation of the monolayer. Upon annealing the surface with a high molecular coverage to 575 K, dibutyl sulfide desorbs molecularly from the less energetically favorable regions of the surface first. At this reduced coverage the system returns to an intermediate-coverage structure, thereby demonstrating the reversibility of the assembly. Elevating the temperature further causes the entire monolayer to desorb, and the original herringbone structure of Au returns. We postulate that this reversibility, coupled with the high rate of concerted rearrangements, allows this system to reach a very high level of order.

Thiocyanate Anchors for Salt-like Iron(II) Complexes on Au(111): Promises and Caveats

“…Tripodal arrangements have been shown before to support stable surface architectures, and SAMs of complex molecules have been successfully prepared using space-demanding tripodal anchors [24 -27]. While thiol groups have been most widely used to attach metal complexes to a gold surface [28,29], some workers have also used thioesters [30 -32], thioethers [27,33,34] or, prior to us, thiocyanates [35]. These 'masked' S-containing functional groups, while retaining a high affinity for gold, are far less reactive towards the central ion in the complex.…”

Asymmetric Thioethers as Building Blocks for Chiral Monolayers

“…In this paper, we extend our previous work on symmetric thioether (RSR) self-assembly [42][43][44] to asymmetric thioethers (RSR 0 ) and show that these monolayers are chiral by virtue of the binding of one of the two pro-chiral lone pairs on the S atom to the Au surface [45]. We find that wellordered domains of butyl methyl sulfide (BMS) and 4,4, 4-trifluorobutyl methyl sulfide (4TF-BMS) form due to van der Waals interactions between molecules, and that the selfassembly is almost 100% enantiospecific, leading to the growth of large homochiral domains.…”

Single Molecular Machines on Semiconductor Surfaces

“…To control the direction of the motion, the use of 1D periodic surfaces or step edges is a good choice to induce a linear movement. Contrary to metallic surfaces, which offer few possibilities to obtain 1D periodic surfaces (Cu-O/Cu [9] or Au(111) [10]), semiconductor or metal-semiconductor interfaces possess a high number of 1D surface reconstructions [11][12][13][14]. Few of them have been tested for molecular motion; nevertheless, the results obtained on InSb or SmSi are very convincing.…”

“…Along the step edges, in the [1][2][3][4][5][6][7][8][9][10] direction, the molecules are very weakly bound to the surface and appear like two protrusions, while in the [110] direction, the molecules are strongly bound to the surface and no change is observed after several scans. On terraces, some noisy horizontal lines indicate mobile molecules while CuPc molecules appear as eight separated protrusions centered over the bright substrate rows, which correspond to the topmost In atoms.…”

“…[17] On the SmSi(111)-5 × 1 reconstruction at room temperature, the DETB appears on STM images like two paired protrusions attributed to the two triptycene wheels. All the DETB molecules are adsorbed onto the large stripes and are self-aligned along the [1][2][3][4][5][6][7][8][9][10] direction with the triptycene wheels above two Sm chains as described in Fig. 6b.…”