Self-assembly and on-surface chemistry of tetraphenyl porphyrin

Self-assembly of molecular building blocks to produce extended two-dimensional arrangements is a first step on the journey towards the design and construction of molecular systems with a predictable structure and functionality. By employing scanning probe techniques such as scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS), an understanding of these self-assembled structures on the single-molecule level can be obtained. When combined with other techniques such as x-ray photoelectron spectrocopy (XPS) and x-ray standing wave analysis (NIXSW), the adsorption geometries and reaction pathways can be extracted to give a completed picture of each system. Within this thesis the self-assembly properties of porphyrin molecules are investigated using scanning probe and photoelectron techniques. Porphyrin molecules have been selected due to their ability to participate in chemical reactions and thier excellent thermal stability. The topography of tetraphenyl porphyrin (TPP) on Au(111) is studied, the local structure and ordering is determined using STM and the average surface arrangement is determined using LEED. The unit cell of the TPP is calculated as well as the commensurability of the lattice with the surface atoms. In addition to an as-deposited close-packed phase, two other visually different phases of TPP on Au(111) are presented and characterised. The arrangement and ordering of the TPP molecules in each phase is quantified using the Voronoi tessellation. The details of the electronic properties of TPP is investigated using STS and kelvin probe force microscopy (KPFM). Using these techniques three electronically distinct species are defined, TPP in the saddle conformation, TPP adsorbing atop a gold atom, and a metalated TPP molecule. Information on the chemical properties of these porphyrin phases is presented, achieved using XPS, by which an additional phase of TPP is observed and further insight into the chemical composition of each phase is achieved. From the XPS fitting a full structural characterisation of each phase is performed using NIXSW. From this the adsorption sites of each chemical species are defined and the heights above the surface extracted. In this thesis the experimental details for all three phases of TPP are presented. The use of a combination of methods allows for a complete picture of system to be built and for access to details that would be otherwise inaccessible. This particular combination of techniques, when used together, can give mechanistic details about the proceedings of chemicals reactions, which has previously been unattainable