Controlling Gold Atom Penetration through Alkanethiolate Self-Assembled Monolayers on Au{111} by Adjusting Terminal Group Intermolecular Interactions

Abstract

The penetration behavior of thermally evaporated Au on S(CH(2))(15)CH(3), S(CH(2))(15)CO(2)CH(3), S(CH(2))(15)CO(2)H, K-modified S(CH(2))(15)CO(2)CH(3), and K-modified S(CH(2))(15)CO(2)H self-assembled monolayers (SAM) on Au substrates is investigated. Gold is a particularly interesting metal since vapor-deposited Au atoms are known to pass through alkanethiolate SAMs on Au{111} substrates at room temperature. Here we show that it is possible to control Au penetration by adjusting the interactions between terminal groups. It is found that Au atoms evenly penetrate into the CH(3) and CO(2)CH(3) films, forming smooth buried layers below the organic thin films. For the CO(2)H film, although Au atoms can still penetrate through it, filaments and mushroomlike clusters form due to H-bonding between film molecules. In the case of the K-modified CO(2)CH(3) or CO(2)H films, however, most Au atoms form islands at the vacuum interface. These results suggest that van der Waals forces and H-bonds are not strong enough to block Au from going through but that ionic interactions are able to block Au penetration. The measurements were performed primarily using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and atomic force microscopy (AFM). The combination of these highly complementary probes provides a very useful strategy for the study of metal atom behavior on SAMs.

Progress with Molecular Electronic Junctions: Meeting Experimental Challenges in Design and Fabrication

“…[10,75] Interactions between end groups of the molecular layer and deposited metals have also been reported for Cu on porphyrin monolayers [84,147] and on SAMs. [130,[148][149][150][151] Notably, particular end-group/top contact metal combinations can yield a chemical association that reduces metal penetration into the monolayer. [150,151] An FTIR study of aromatic monolayers bonded to Si via SiÀC bonds derived from diazonium reduction reported that soft deposition of 100 nm of Au produced minor perturbations of the IR spectrum, while direct e-beam deposition of the same thickness caused serious degradation of the aromatic structure of the monolayer.…”

Mechanical and Charge Transport Properties of Alkanethiol Self-Assembled Monolayers on a Au(111) Surface: The Role of Molecular Tilt

“…Potential changes to consider include distortions of the S-Au binding configuration, and displacement of gold atoms, including formation of metal filaments as proposed by some authors [37].…”

The study of charge transport through organic thin films: mechanism, tools and applications

“…Nanofabrication results in junctions able to trap a much smaller number of molecules: the evaporation of gold through a nanopore mask on top of a SAM reduces the area of the junction to less than 300 mm 2 , and therefore reduces the probability of incorporating defects in the junctions (but also the current). Although these systems have demonstrated interesting functionalities, there has been little characterization (Zhu et al 2006;Walker et al 2007) of the nature of the interface formed by the evaporation of metal atoms onto organic films, and electrical shorts due to the percolation of Au atoms through the film (and probably other types of defects) have limited the reproducibility of the results.…”