In Situ Scanning Tunneling Microscopy of 1,6-Hexanedithiol, 1,9-Nonanedithiol, 1,2-Benzenedithiol, and 1,3-Benzenedithiol Adsorbed on Pt(111) Electrodes

Abstract

Cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) were used to examine four dithiol molecules, including 1,6-hexanedithiol, 1,9-nonanedithiol, 1,2-benzenedithiol, and 1,3-benzenedithiol, adsorbed on well-ordered Pt(111) electrodes in 0.1 M HClO(4). The open-circuit potential (OCP) of Pt(111) electrodes decreased substantially from 0.95 to 0.3 V (versus reversible hydrogen electrode) upon the adsorption of dithol molecules, which indicates that these adsorbates injected electrons into the Pt electrode. For all dithiol molecules, ordered adlattices of p(2 x 2) and (square root 3 x square root 3)R30 degrees were formed when the dosing concentration was lower than 150 microM and the potential of Pt(111) was more negative than 0.5 V. Raising the potential of Pt(111) from 0.1 to 0.4 V or more positive values could transform p(2 x 2) to (square root 3 x square root 3)R30 degrees before it turned disarray. The insensitivity of the structure of dithiol adlayers with their chemical structures was explained by upright molecular orientation with the formation of one Pt-S bond per dithiol molecule. This molecular orientation was independent of the coverage of dithiol molecules, as nucleation seeds produced at the beginning of adsorption were also constructed with p(2 x 2). The triangular-shaped STM molecular resolution suggested 3-fold binding of sulfur headgroup on Pt(111). All dithiols were adsorbed so strongly on Pt(111) electrodes that switching the potential negatively to the onset of hydrogen evolution in 0.1 M HClO(4) or water reduction in 1 M KOH could not displace dithiol admolecules.

Electrical conduction through single molecules and self-assembled monolayers

“…By using a conducting sample, a SAM of alkane(di)thiols on top of a metal film can be studied, see figure 3. Its usability makes STM one of the most widely used techniques to study molecular monolayers [23,24,[55][56][57][58][59][60][61][62][63], even though alkanedithiols might chemisorb to the STM tip. The STM is capable of recording very small currents.…”

Going beyond the self-assembled monolayer: metal intercalated dithiol multilayers and their conductance

“…It should be noted that interest in molecules with phenyl units is related to the fact that they have better conducting properties and are better adapted as molecular contacts between nanosized metallic electrodes. [7][8][9][10][11][12][13][14][15][16][17][18] Indeed, the rst conduction measurements on molecules involved measuring the resistance of a 1,4-benzenedimethanethiol (BDMT) molecule. 19 This was performed using a scanning tunneling microscopy (STM) tip held on a gold nanoparticle deposited on top of a BDMT SAM.…”

Large-area molecular junctions

“…By using a conducting sample, a SAM of alkane(di)thiols on top of a metal film can be studied, see Figure 1.3. Its usability makes STM one of the most widely used techniques to study molecular monolayers [23,24,55,56,57,58,59,60,61,62,63], even though alkanedithiols might chemisorb to the STM tip. The STM is capable of recording very small currents.…”