STM Investigations of Thiol Self-Assembled Monolayers

Abstract

The most‐studied thin organic monolayers—which have applications in many areas of science and technology—are self‐assembled monolayers (SAMs) of alkanethiols. Scanning tunneling microscopy (STM) of alkanethiol SAMs on Au(111) surfaces reveals small holes or defects, whose origin is a current topic of discussion. The STM investigation reported here of thiosalicylic acid on Au(111) reveals not holes but disordered structures. Comparison of the two sets of measurements provides new aspects for consideration with regard to the origin of the hole defects in thiol selfassembled films.

Effect of Ring Substitution Position on the Structural Conformation of Mercaptobenzoic Acid Self-Assembled Monolayers on Au(111)

“…Even so, the resistance of the monolayers to disruption via dimerization implies that there are strong intermolecular interactions between neighboring adsorbates. Given that there is negligible hydrogenbonding between the carboxyl groups of neighboring 4-MBA molecules bound to Au(111) [28] [12]. It has been demonstrated [44,45] that organothiol monomers with molecular structures comparable to 4-MBA exhibit well-defined monolayer arrangements and intermolecular packing.…”

“…Even so, alternative monolayer structures, such as those based upon π-π van der Waals interactions, cannot be excluded by analysis of the molecular tilt angle alone. It is important to state that comparison of the tilt angle with the STM images [12] reported for 4-MBA on Au(111) does not provide a more definitive assignment of the monolayer packing. Although the images display a periodic row structure, the closest approach between bright features is 8Å.…”

“…In contrast, the alkyl chains in MA exhibit more insulating properties [26]. Secondly, MBAs form extremely thin SAMs (< 8Å), which have been shown via STM [12] to contain a high degree of structural order. This is significant because SAMs of comparable thickness prepared from 'short chain' MAs contain substantial disorder [27].…”

Single Electron Tunneling Through Nano-Sized Cobalt Particles

“…The most commonly utilized explanation invokes substrate vacancy islands generated by chemical erosion during the self-assembly process. [35,36] At higher resolution (Fig. 2B), the molecular ordering is clearly observed: Thiol molecules show a characteristic brush-like arrangement of the alkyl chains with the sulfur head group ordering into (v3´v3) R30 structures (Fig.…”

Perspectives on Thin Molecular Organic Films

“…Recent reports of functional systems incorporating molecular films include light-emitting diodes (LEDs), [43±48] lasers, [49] magnetic shielding materials, [50] nonlinear optical materials, [51] field-effect transistors (FETs), [36,52±56] rectifying junctions, [57,58] photovoltaic devices, [59,60] and biosensors. [61,62] Thin organic films are usually obtained by organic chemicalvapor deposition (OCVD), [6,63,64] physical vacuum deposition (PVD), [65±68] organic vapor-phase deposition (OVPD), [69] organic molecular-beam deposition (OMBD), [70±73] co-evaporation, [74,75] Langmuir±Blodgett (LB) [76] and self-assembled monolayers (SAM) techniques, [77,78] and electrochemical crystallization. [79±81] Recently, the preparation of thin single crystals by confined electrocrystallization has also been reported.…”