Elucidation of the deposition processes and spatial structures of alkanethiol and arylthiol molecules adsorbed on Pt(111) electrodes with in situ scanning tunneling microscopy

Yaw Chia Yang, Ya Pei Yen, Liang Yueh Ou Yang, Shueh Lin Yau, Kingo Itaya

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33 Scopus citations

Abstract

In situ scanning tunneling microscopy (STM) was used to examine the spatial structures of n-alkane thiols (1-hexanethiol, 1-nonanethiol, and 1-octahexanethiol) and arylthiols (benzenethiol and 4-hydroxy-benzenethiol) adsorbed on well-ordered Pt(111) electrodes in 0.1 M HClO4. The electrochemical potential and molecular flux were found to be the dominant factors in determining the growth mechanisms, final coverages, and spatial structures of these organic adlayers. Depending on the concentrations of the thiols, deposition of self-assembled monolayers (SAMs) followed either the nucleation-and-growth mechanism or the random fill-in mechanism. Low and high thiol concentrations respectively produced two ordered structures, (2 × 2) and (√3 × √3)A30°, between 0.05 and 0.3 V. On average, an ordered domain spanned 500 Å when the SAMs were made at 0.15 V, but this dimension shrank substantially once the potential was raised above 0.3 V. This potential-induced order-to-disorder phase transition resulted from a continuous deposition of thiols, preferentially at domain boundaries of (√3 × √3)R30° arrays. All molecular adlayers were completely disordered by 0.6 V, and this restructuring event was irreversible with potential modulation. Since all thiols were arranged in a manner similar to that adopted by sulfur adatoms (Sung et al. J. Am. Chem. Soc. 1997, 119, 194), it is likely that they were adsorbed mainly through their sulfur headgroups in a tilted configuration, irrespective of the coverage. Both the sulfur and phenyl groups of benzenethiol admolecules gave rise to features with different corrugation heights in the molecular-resolution STM images. All thiols were adsorbed strongly enough that they remained intact at a potential as negative as -1.0 V in 0.1 M KOH.

Original languageEnglish
Pages (from-to)10030-10037
Number of pages8
JournalLangmuir
Volume20
Issue number23
DOIs
StatePublished - 9 Nov 2004

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