Biography

Federico Williams is an Associate Professor at the University of Buenos Aires and a Principal Researcher at the National Scientific and Technical Research Council (CONICET, Argentina). He obtained his PhD in Physical Chemistry from the University of Cambridge in 2001. He subsequently held several research fellowships at Cambridge, including the Oppenheimer Fellowship in the Department of Chemistry (2000–2003), the Trapnell Fellowship at King’s College (2001–2005), and a Leverhulme Trust Early Career Fellowship (2003–2005). In 2018–2019, he was a Visiting Professor at Friedrich-Alexander-Universität Erlangen–Nürnberg, supported by a Mercator Fellowship from the German Research Foundation (DFG).

His research focuses on the elucidation of fundamental processes at surfaces and interfaces, with particular emphasis on: (i) the interaction and reactivity of transition metal complexes on solid substrates and ionic liquids, (ii) interfacial mechanisms in lithium battery systems, and (iii) the electronic structure and organization of self-assembled monolayers. To address these problems, he employs a wide range of experimental techniques, including synchrotron-based methods, scanning probe microscopies, and photoelectron spectroscopies.

Website: http://superficies.qi.fcen.uba.ar

Title

Engineering Energy-Level Alignment at Molecule–Semiconductor Interfaces

Abstract

Controlling energy-level alignment at molecule–semiconductor interfaces is central to hybrid systems for light-driven applications. In this talk I will present a combined X-ray photoelectron spectroscopy and density functional theory study of ruthenium polypyridine complexes adsorbed on rutile TiO₂(110), a model oxide surface. The molecules form stable monolayers anchored via deprotonated carboxylate groups, preserving their coordination upon adsorption.

We show that ligand substitution systematically tunes the HOMO relative to the TiO₂ valence band, while the LUMO remains largely unchanged, enabling controlled modification of interfacial dipoles and work function. Extending this approach to a cyanide-bridged biruthenium complex, we find that its LUMO aligns with the TiO₂ conduction band, enabling electron injection, while the hole is localized on the metal center distal from the surface, potentially suppressing recombination.

These results demonstrate how molecular design enables control of band alignment and charge-transfer processes at oxide interfaces.