Study of Molecule-Metal Interfaces by Means of the Normal Incidence X-ray Standing Wave Technique

This work investigates the geometric and chemical properties of different moleculemetal interfaces, relevant to molecular electronics and functional surfaces applications, by means of the normal incidence x-ray standing wave (NIXSW) technique. All NIXSW data are analysed by means of the newly developed open-source program Torricelli, which is thoroughly documented in the thesis. In order to elucidate the role played by the substrate within molecule-metal interfaces, the prototype organic molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on the Ag(110) surface is investigated. The molecule results more distorted and at smaller bonding distances on the more reactive Ag(110) surface, in comparison with the Ag(100)$^{1}$ and the Ag(111)$^{2}$ substrates. This conclusion follows from the detailed molecular adsorption geometry obtained from the differential analysis of both carbon and oxygen atoms. Subsequently, the chemisorptive PTCDA/Ag(110) interaction is tuned by the codeposition of an external alkali metal, namely K. As a consequence, the functional groups of PTCDA unbind from the surface, which, in turn, undergoes major reconstruction. In fact, the resulting nanopatterned surface consists of alternated up and down reconstructed Ag terraces covered by PTCDA molecules partly unbound with respect to the pure molecular phase. Within the context of the functional surfaces, the interaction of the molecular switches azobenzene (AB) and 3,3,5,5-tetra-tert-butyl-azobenzene (TBA) adsorbed on the Ag(111) surface is investigated. The bonding distance of TBA, only slightly greater compared to AB, indicates that the desired geometric decoupling of the photochromic moiety to enable the switching in the adsorbate state does not occur.$^{3}$ In [...