title: Self-assembled monolayers of cobalt(II)- (4-tert-butylphenyl)-porphyrins: the influence of the electronic dipole on scanning tunneling microscopy images.
abstract: Self-assembled monolayers (SAMs) of cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin, a promising material for optical, photoelectrochemical, and chemical sensor applications, were prepared on Au(111) via axial ligation to 4-aminothiophenol, and studied by several surface science techniques. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements showed the apparent topology of the Au(111) herringbone structure reconstruction, but with bias-dependent contrast images and asymmetric I/V characteristics. Photoelectron spectroscopy confirmed the presence of metalloporphyrins on the surface, whereas near-edge X-ray absorption (NEXAFS) measurements revealed that the porphyrin ring was tilted by about 70 degrees with respect to the surface plane. The above effects are ascribed to the presence of oriented molecular dipole layers between the metal and the organic material as confirmed by a comparison with first-principles density-functional theory calculations. The measured bias-dependent STM profiles have been reproduced by a simple monodimensional tunneling model.
authors.affiliation: National Nanotechnology Laboratory of INFM, Distretto Tecnologico ISUFI, Università di Lecce, Via Arnesano, 73100 Lecce, Italy. valentina.arima@unile.it
authors.forename: Valentina
authors.initials: V
authors.lastname: Arima
authors.forename: Eduardo
authors.initials: E
authors.lastname: Fabiano
authors.forename: Robert I R
authors.initials: RI
authors.lastname: Blyth
authors.forename: Fabio
authors.initials: F
authors.lastname: Della Sala
authors.forename: Francesca
authors.initials: F
authors.lastname: Matino
authors.forename: Julie
authors.initials: J
authors.lastname: Thompson
authors.forename: Roberto
authors.initials: R
authors.lastname: Cingolani
authors.forename: Ross
authors.initials: R
authors.lastname: Rinaldi