Adsorbed Structures of 4,4‘-Bipyridine on Cu(111) in Acid Studied by STM and IR

Abstract

The adsorption of 4,4'-bipyridine (BiPy) on Cu(111) has been investigated in 0.1 M HClO4 by cyclic voltammetry, electrochemical scanning tunneling microscopy (STM), and surface-enhanced infrared adsorption spectroscopy (SEIRAS). Cyclic voltammetry showed the double layer region extending from -0.2 to 0.26 V and a pair of redox waves superposing on hydrogen evolution wave at more negative potentials. Diprotonated BiPy, BiPyH2(2+), is adsorbed flat on the Cu(111) (1 x 1) surface and forms a well-ordered monolayer with a (3 x 4) symmetry in the double-layer potential region. At more negative potential, BiPyH2(2+) is reduced to its monocation radical, BiPyH2(*+), and forms another well-ordered structure in which the radicals are stacked in molecular rows with a face-to-face self-dimer as the building unit. The SEIRA spectra of both BiPyH2(2+) and BiPyH2(*+) are dominated by gerade modes which should be IR-inactive for the centrosymmetric species. The breakdown of the selection rule of IR absorption is ascribed to the vibronic coupling associated with charge transfer between BiPyH2(2+) and the surface and between the radicals.

Nanoscale Insights into Enhanced Raman Spectroscopy

“…Figure 8f shows a Raman spectrum taken within the area of a large 3D island using a confocal Raman unit. The spectrum above 1000 cm −1 is consistent with the Raman spectrum of a solid BiPyH 2 Cl 2 [59].…”

Molecular Self-Assembly at Metal-Electrolyte Interfaces

“…In electrochemical environments viologen species are well known to exist in three oxidation states, namely as dicationic species (V 2+ ), radical monocations V +• and uncharged viologen molecules V 0 , respectively [27,28]. Charge transfer reactions within adsorbed ordered layers of viologens as a function of the electrode potential are reported to result in reversible structure transitions [29,30]. For instance, adsorption of 2.2′-bipyridine molecules on a Au(111) surfaces in HClO 4 acidic solution was reported by Wandlowski et al [29].…”

Seeded growth fabrication of Cu-on-Si electrodes for in situ ATR-SEIRAS applications

“…A key issue for successfully implementing this technique is to fabricate appropriate nanoparticle metal films that can produce strong SEIRA effect while maintain essentially the same electrochemical properties as their bulk counterparts. Recently triggered by the effort in Osawa's group [24], simple wet fabrication techniques [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] (including chemical deposition and electrochemical deposition of metallic nanoparticle films on an IR window such as Si and Ge) are developing rapidly, with an expectation to replace the traditional and expensive dry process fabrication (including vacuum evaporation and sputtering). A SEIRA-active Cu film chemically deposited on a Ge element has been reported [29].…”