Adatoms at the Sulfur–Gold Interface in 1-Adamantanethiolate Monolayers, Studied Using Reaction with Hydrogen Atoms and Scanning Tunneling Microscopy

Abstract

Scanning tunneling microscopy is used to study monolayers of 1-adamantanethiolate as they are exposed to gas-phase atomic hydrogen. H-atom reaction results in complete removal of the organic monolayer. The relaxation of the reconstruction present at the gold–sulfur interface results in the formation of gold-atom islands, as well as the addition of gold atoms to extant surface defects such as steps and pits. Characterization of these changes shows that for 1-adamantanethiolate monolayers, 0.18 ± 0.033 monolayers of gold adatoms participate in bonding with thiolate sulfur atoms. This results in a 1:1 Au:S ratio, in contrast to the 1:2 Au:S ratio reported for n-alkanethiolate monolayers. The difference in adatom density implies a qualitative difference in binding between n-alkanethiols and 1-adamantanethiols.

From the bottom up: dimensional control and characterization in molecular monolayers

“…Cage molecules such as adamantanes and carboranes are classes of SAM substituents in which the cage serves as a short, sterically bulky backbone. 6,82,122,123 Thiolated cage molecules thus have large molecular lattice constants relative to alkanethiols (B0.7 nm vs. 0.5 nm), and weaker intermolecular interactions, 124 meaning they are easily displaced from Au{111} surfaces by alkanethiols. 6,123 Adamantane cages can be engineered to orient normal or tilted relative to the surface, by thiolating at either a primary (2-adamantanethiol) or tertiary (1-adamantanethiol) carbon, making it possible to create or to eliminate tilt defects based on small changes in molecular structure.…”

Chain-Length-Dependent Reactivity of Alkanethiolate Self-Assembled Monolayers with Atomic Hydrogen

“…Several groups have studied thiolate SAM reactivity with energetic gas species such as H, ,− O, − and O 3 , − as adsorption energetics and reaction dynamics are of great interest to the surface science community. For example, techniques such as X-ray photoelectron spectroscopy , and reflection absorption infrared spectroscopy have been used to explore the effect of chain length on the reactivity of alkanethiolate SAMs with atomic gases.…”

Communication: Scanning tunneling microscopy study of the reaction of octanethiolate self-assembled monolayers with atomic chlorine

“…[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Our lab has previously completed a series of experiments utilizing scanning tunneling microscopy (STM) to understand and quantify the mechanism of reactions of various alkanethiolate SAMs with atomic hydrogen. [22][23][24][25] The molecular-scale information provided by STM shows that for these reactions, the number and position of defects with the monolayer plays an important role in controlling reactivity. For octanethiol SAMs, molecules in sites near either substrate steps or orientation defects were over 500 times more reactive than molecule in close-packed regions of the surface.…”