The basic principle of the STM experiment is described in Sect. 2.1. A theoretical basis for the treatment of electron tunneling in STM is given by Bardeen’s theory [1], which is the preeminent quantitative theory of the tunneling current in STM [2]. It was published in 1961 and applied to the STM in 1983 by Tersoff and Hamann [3] (Sect. 2.2). The latter method is incorporated into nearly every state of the art density functional theory (DFT) code. A simpler model was proposed by Selloni et al. and Lang [4, 5], making use of the Wentzel–Kramers–Brillouin (WKB) approximation. This will be discussed with respect to Scanning Tunneling Spectroscopy (STS) (Sect. 2.3). A discussion about the contrast mechanism of organic adsorbates on solid surfaces in STM images is presented in Sect. 2.4. Other experimental methods, which were used in the work at hand are Temperature Programmed Desorption (TPD) (Sect. 2.5) and Low Energy Electron Diffraction (LEED) (Sect. 2.6).