Journal of Electron Spectroscopy and Related Phenomena 151 (2006) 45–51 A detailed analysis of the photoemission spectra of basic thioaromatic monolayers on noble metal substrates A. Shaporenko a , A. Terfort b , M. Grunze a , M. Zharnikov a,∗ a Angewandte Physikalische Chemie, Universit¨ at Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany b Anorganische und Angewandte Chemie, Universit¨ at Hamburg, 20146 Hamburg, Germany Received 8 September 2005; received in revised form 25 October 2005; accepted 25 October 2005 Available online 28 November 2005 Abstract Analysis of photoemission spectra of complex thioaromatic self-assembled monolayers (SAMs) requires the knowledge and understanding of such spectra for the basic systems. Keeping this goal in mind, synchrotron-based high-resolution X-ray photoelectron spectroscopy was used to characterize SAMs formed from the simplest thioaromatic compounds, namely thiophenol, 1,1 ′ -biphenyl-4-thiol and 1,1 ′ ;4 ′ ,1 ′′ -terphenyl-4-thiol on evaporated Au(1 1 1) and Ag(1 1 1) substrates. The acquired S 2p and C 1s spectra were analyzed in terms of fine structure and initial and final state effects in the photoemission process. The assignment of the individual spectral features was considered in detail. Conclusions on quality and chemical and structural homogeneity of the investigated SAMs were derived. © 2005 Elsevier B.V. All rights reserved. Keywords: Self-assembled monolayers; High-resolution X-ray photoelectron spectroscopy; Initial and final state effects in the photoemission 1. Introduction The emergence of molecular electronics [1–3] and other new technologies ranging from sensor fabrication [4] to chemical lithography [5–7] has triggered significant interest in aromatic thiol-derived self-assembled monolayers (SAMs) (see, e.g. refs. [1,8–22]). The applications of these SAMs rely on a precise knowledge of their properties, which requires their detailed characterization by advanced spectroscopic and microscopic techniques. Among these techniques X-ray photoemission spec- troscopy (XPS) is of particular importance, since it is a powerful and widespread method available in many laboratories over the world. For the correct analysis and interpretation of the XPS spectra of different aromatic thiol-derived SAMs, reference information about the spectra of the simplest representatives of this class of SAMs is desirable. In this communication, we provide a detailed analysis of high-resolution XPS (HRXPS) spectra of SAMs formed from thiophenol (TP); 1,1 ′ -biphenyl-4-thiol (BPT); 1,1 ′ ;4 ′ ,1 ′′ - ∗ Corresponding author. Tel.: +49 6221 544921; fax: +49 6221 54 6199. E-mail address: Michael.Zharnikov@urz.uni-heidelberg.de (M. Zharnikov). terphenyl-4-thiol (TPT) on evaporated Au(1 1 1) and Ag(1 1 1) substrates, which are standard substrates for the fabrication of thiol-derived SAMs. These non-substituted thioaromatic com- pounds vary in the number of aromatic rings and are described by the general formula C 6 H 5 –(C 6 H 4 ) n –SH with n = 0, 1 and 2 for TP, BPT and TPT, respectively. Thus, the effect of chain length on the SAM properties can be monitored. Note that while XPS and even HRXPS data for some of the SAMs under consideration can be found in the literature [15,17,20,23–26], no systematic high-quality data on the entire series is available. From previous work [1,8–10,13,15,17], it is well known that the molecules in this study form highly oriented and densely packed SAMs on both Au and Ag substrates, with the exception of poorly defined TP films on Au. The molecular orientation and orientational order of the molecular constituents in these SAMs depend on the length of the aromatic backbone and the substrate [8,17]. The molecules, which on average are slightly inclined with respect to the surface normal, show a less tilted orientation with increasing length of this backbone and, similar to alkanethiolate SAMs [27,28], exhibit smaller tilt angles on Ag than on Au. In the following section, we describe the experimental pro- cedures and techniques. The results are presented and briefly 0368-2048/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2005.10.008