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Simulating Surface Spectroscopy of Single Atom Magnets and Catalysts

reinhard
Supervisors: Reinhard Maurer (Chemistry), Julie Staunton (Physics)
External Project Partners: Diamond Light Source & Duke University

Functional materials for catalysis and magnetooptical applications often contain precious materials, the scarcity of which is a strong motivation for maximizing the efficiency of their use. Single atoms can act as catalysts (Single atom catalysts, SACs) or single atom magnets (SAMs) when stabilized on well-defined substrates. SAC/SAM materials are often studied with X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, but the rich structure and overlapping features make these spectra hard to disentangle. This project will develop new simulation methodology to predict such complex spectroscopic signatures and, in collaboration with experimental partners, novel SAM and SAC materials will be characterized.

Functional materials for catalysis and magnetooptical applications often contain precious materials, the scarcity of which is a strong motivation for maximizing the efficiency of their use. This can be achieved by reducing the concentration of precious metal atoms while retaining or even improving their functionality as reactive or magnetic centres. In the extreme limit, single atoms can act as catalysts (Single atom catalysts, SACs) or single atom magnets (SAMs) when stabilized on well-defined substrates. [1,2]

X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD) play an important role in characterizing the structure, electronic and magnetic state of stabilized single atoms. The rich structure and overlapping features present in experimental XPS and NEXAFS spectra often provide a challenge to the unambiguous assignment of all peaks. Here, the theoretical analysis and computational simulation of the electronic structure and core-level transitions can yield new insights. The first-principles-based simulation of core-level spectra is established [3], however, almost all practical electronic structure methods can only reliably predict spectra originating from excitation of 1s states. Experimentally, the electronic and magnetic states of single metal atoms are best characterized by probing core-states with higher angular momentum, such as 2p, 3d or 4f-type orbitals, for which simulation techniques are still lacking.

In this project, you will develop an efficient but approximate methodology to simulate core-level spectra of 2p, 3d and 4f states, which are important for the analysis of the chemical and magnetic state of SAMs and SACs. In collaboration with experimental partners, the new methods will be applied to understand X-ray spectroscopy experiments on surface-supported single atoms with high magnetic moments. The new methods will be developed within an established electronic structure software package by combining state-of-the-art methods for spin-orbit coupling, strong correlation, and core-hole constraints.

[1] DOI: 10.1021/acs.chemrev.0c00576 (2020); Nature 543, 226–228 (2017); [2] Curr. Opin. Green Sustain. Chem. 22, 54–64 (2020); [3] Klein, Hall, Maurer, https://arxiv.org/abs/2010.10437 (2020)