Polaron pattern recognition
in correlated oxide surfaces

@article{Franchini2021,

title = {Polarons in materials},

author = {Cesare Franchini and Michele Reticcioli and Martin Setvin and Ulrike Diebold},

doi = {10.1038/s41578-021-00289-w},

year  = {2021},

date = {2021-03-19},

journal = {Nature Reviews Materials},

publisher = {Springer Science and Business Media LLC},

abstract = {Polarons are quasiparticles that easily form in polarizable materials due to the coupling of excess electrons or holes with ionic vibrations. These quasiparticles manifest themselves in many different ways and have a profound impact on materials properties and functionalities. Polarons have been the testing ground for the development of numerous theories, and their manifestations have been studied by many different experimental probes. This Review provides a map of the enormous amount of data and knowledge accumulated on polaron effects in materials, ranging from early studies and standard treatments to emerging experimental techniques and novel theoretical and computational approaches.},

keywords = {P02, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Hulva2021,

title = {Unraveling CO adsorption on model single-atom catalysts},

author = {Jan Hulva and Matthias Meier and Roland Bliem and Zdenek Jakub and Florian Kraushofer and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},

doi = {10.1126/science.abe5757},

year  = {2021},

date = {2021-01-22},

urldate = {2021-01-22},

journal = {Science},

volume = {371},

number = {6527},

pages = {375--379},

publisher = {American Association for the Advancement of Science (AAAS)},

abstract = {Understanding how the local environment of a “single-atom” catalyst affects stability and reactivity remains a challenge. We present an in-depth study of copper_{1}, silver_{1}, gold_{1}, nickel_{1}, palladium_{1}, platinum_{1}, rhodium_{1}, and iridium_{1} species on Fe_{3}O_{4}(001), a model support in which all metals occupy the same twofold-coordinated adsorption site upon deposition at room temperature. Surface science techniques revealed that CO adsorption strength at single metal sites differs from the respective metal surfaces and supported clusters. Charge transfer into the support modifies the d-states of the metal atom and the strength of the metal–CO bond. These effects could strengthen the bond (as for Ag_{1}–CO) or weaken it (as for Ni_{1}–CO), but CO-induced structural distortions reduce adsorption energies from those expected on the basis of electronic structure alone. The extent of the relaxations depends on the local geometry and could be predicted by analogy to coordination chemistry.},

keywords = {P02, P04, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Jakub2019,

title = {Local Structure and Coordination Define Adsorption in a Model Ir_{1}/Fe_{3}O_{4} Single-Atom Catalyst},

author = {Zdenek Jakub and Jan Hulva and Matthias Meier and Roland Bliem and Florian Kraushofer and Martin Setvin and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},

doi = {10.1002/anie.201907536},

year  = {2019},

date = {2019-07-24},

urldate = {2019-07-24},

journal = {Angewandte Chemie - International Edition},

volume = {58},

number = {39},

pages = {13961--13968},

publisher = {Wiley},

abstract = {Single-atom catalysts (SACs) bridge homo- and heterogeneous catalysis because the active site is a metal atom coordinated to surface ligands. The local binding environment of the atom should thus strongly influence how reactants adsorb. Now, atomically resolved scanning-probe microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and DFT are used to study how CO binds at different Ir_{1} sites on a precisely defined Fe_{3}O_{4}(001) support. The two- and five-fold-coordinated Ir adatoms bind CO more strongly than metallic Ir, and adopt structures consistent with square-planar Ir^{I} and octahedral Ir^{III} complexes, respectively. Ir incorporates into the subsurface already at 450 K, becoming inactive for adsorption. Above 900 K, the Ir adatoms agglomerate to form nanoparticles encapsulated by iron oxide. These results demonstrate the link between SAC systems and coordination complexes, and that incorporation into the support is an important deactivation mechanism.},

keywords = {P02, P04, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Reticcioli2019,

title = {Interplay between Adsorbates and Polarons: CO on Rutile TiO_{2}(110)},

author = {Michele Reticcioli and Igor Sokolović and Michael Schmid and Ulrike Diebold and Martin Setvin and Cesare Franchini},

doi = {10.1103/physrevlett.122.016805},

year  = {2019},

date = {2019-01-09},

journal = {Physical Review Letters},

volume = {122},

number = {1},

pages = {016805},

publisher = {American Physical Society (APS)},

abstract = {Polaron formation plays a major role in determining the structural, electrical, and chemical properties of ionic crystals. Using a combination of first-principles calculations, scanning tunneling microscopy, and atomic force microscopy, we analyze the interaction of polarons with CO molecules adsorbed on the reduced rutile TiO_{2}(110) surface. Adsorbed CO shows attractive coupling with polarons in the surface layer, and repulsive interaction with polarons in the subsurface layer. As a result, CO adsorption depends on the reduction state of the sample. For slightly reduced surfaces, many adsorption configurations with comparable adsorption energies exist and polarons reside in the subsurface layer. At strongly reduced surfaces, two adsorption configurations dominate: either inside an oxygen vacancy, or at surface Ti_{5c} sites, coupled with a surface polaron. Similar conclusions are predicted for TiO_{2}(110) surfaces containing near-surface Ti interstitials. These results show that polarons are of primary importance for understanding the performance of polar semiconductors and transition metal oxides in catalysis and energy-related applications.},

keywords = {P02, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Reticcioli2017,

title = {Polaron-Driven Surface Reconstructions},

author = {Michele Reticcioli and Martin Setvin and Xianfeng Hao and Peter Flauger and Georg Kresse and Michael Schmid and Ulrike Diebold and Cesare Franchini},

doi = {10.1103/physrevx.7.031053},

year  = {2017},

date = {2017-09-25},

urldate = {2017-09-25},

journal = {Physical Review X},

volume = {7},

number = {3},

pages = {031053},

publisher = {American Physical Society (APS)},

abstract = {Geometric and electronic surface reconstructions determine the physical and chemical properties of surfaces and, consequently, their functionality in applications. The reconstruction of a surface minimizes its surface free energy in otherwise thermodynamically unstable situations, typically caused by dangling bonds, lattice stress, or a divergent surface potential, and it is achieved by a cooperative modification of the atomic and electronic structure. Here, we combined first-principles calculations and surface techniques (scanning tunneling microscopy, non-contact atomic force microscopy, scanning tunneling spectroscopy) to report that the repulsion between negatively charged polaronic quasiparticles, formed by the interaction between excess electrons and the lattice phonon field, plays a key role in surface reconstructions. As a paradigmatic example, we explain the (1×1) to (1×2) transition in rutile TiO_{2}(110).},

keywords = {P02, P03, P07, pre-TACO},

pubstate = {published},

tppubtype = {article}

}