Tip-enhanced Raman spectroscopy of 4,4′-bipyridine and 4,4′-bipyridine N,N'-dioxide adsorbed on gold thin films

• Published in: Surface science Vol. 617; pp. 1 - 9
• Main Authors: Rzeźnicka, I.I., Horino, H., Kikkawa, N., Sakaguchi, S., Morita, A., Takahashi, S., Komeda, T., Fukumura, H., Yamada, T., Kawai, M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.11.2013; Elsevier
• Subjects: 4,4′-bipyridine; 4,4′-bipyridine N; Adsorption; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Gold; Monolayers; N'-dioxide; Physics; Raman spectroscopy; Raman tensor; Stretching; Surface chemistry; Thin films; Tip-enhanced Raman spectroscopy; Vertical orientation; Vibration; 4,4′-bipyridine; Raman tensor; N'-dioxide; Au; Tip-enhanced Raman spectroscopy; 4,4′-bipyridine N; Thin films; 4,4'-bipyridine N; Gold; Raman spectra; 4,4'-bipyridine; Transition elements
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2013.08.010

A tip-enhanced Raman spectroscopy (TERS) set-up added on a scanning tunneling microscope (STM) was constructed and was used to study the molecular arrangement of 4,4′-bipyridine (4,4′-BiPy) and 4,4′-bipyridine N,N'-dioxide (4,4′-BiPyO2) adsorbed on Au(111). Over a monolayer of 4,4′-BiPy, in the ambient atmosphere, intense TERS signals were recorded, involving AuN stretching vibration at 185cm−1. At the early stage of 4,4′-BiPy adsorption, the AuN stretching signal was not detected. By the aid of the theoretical calculations of the Raman scattering intensities for each vibrational normal mode, a standing-up, tilted orientation at monolayer coverage and a vertical orientation with the longitudinal molecular axis parallel to the surface at low surface coverage was concluded. Adsorption of 4,4′-BiPyO2 on Au(111) resulted in formation of a (6×9) adlattice. Moderately intense TERS signals were observed, containing the NO stretching modes and the in-plane ring vibrational modes. Neither AuO nor AuN stretching modes were observed. 4,4′-BiPyO2 was laid with the longitudinal axis parallel to the surface, and the molecular plane vertical to the surface. These results demonstrate that STM-TERS is an effective method for simultaneous imaging and vibrational analysis, facilitating identification of the adsorbed layers with the nanometer-scale spatial resolution and monolayer sensitivity. [Display omitted] •STM of 4,4’-bipyridine and 4,4’-bipyridine N,N’-dioxide adlayers on Au(111).•Nanoimaging combined with vibrational analysis.•The Au-N stretching indicates chemisorption of 4,4’-bipyridine on Au(111).•Molecular orientation is deduced from calculation of Raman tensor elements.