Surface structure and reactivity of
multi-component oxides at the atomic scale
Subproject P02
Multi-component metal oxides exhibit a plethora of stoichiometry-dependent structural phases at the surface, even if the composition of the bulk is kept the same. The long-term objective of P02 is to unravel the relationship between surface electronic and geometric structure and reactivity, to ultimately tune these materials for energy-related reactions such as the ORR. The project applies the surface science approach. We will grow well-defined, epitaxial perovskite thin films of LSFO and LSMO in a UHV-based PLD/surface science apparatus under tight control of the surface stoichiometry in the first project period. We will determine the coordinates of surface atoms quantitatively using LEED-IV in close collaboration with theoretical groups.
Theoretical models will also help with interpreting atomically-resolved ncAFM/STM images. These images give direct insights into the behavior of polarons in these complex materials and show how adsorbates such as O2, H2O, CO, and CO2 interact with electronic and structural defects. XPS, TPD, and FTIR of these well-defined systems will deliver desorption energies, vibrational frequencies, and spectral fingerprints. These experimental data on well-defined systems will build a bridge when tested under ‘realistic’ environments at high pressure/temperature and in aqueous solutions. They will also serve to validate ML-based theory approaches.
Expertise
Our expertise is experimental surface science. We operate a total of seven ultrahigh-vacuum (UHV) chambers, which contain virtually all main experimental surface science techniques, as well as an (electro-)chemistry lab.
All chambers are equipped with facilities for sample preparation (sputtering/annealing/gas dosing), as well as various growth techniques (e-beam evaporators, Knudsen cells, UHV-compatible sputter deposition, pulsed laser deposition (PLD)).
Analysis techniques used in our research include:
- Scanning Tunneling Microscopy (STM) (in UHV 4K – 300 K, electrochemical STM)
- Atomic Force Microscopy (AFM): UHV-based (q+ sensor) and in the ambient (cantilever-based)
- Low-Energy Electron Diffraction (LEED)
- Reflection High Energy Diffraction (RHEED)
- X-ray Photoelectron Spectroscopy (XPS)
- Ultraviolet Photoelectron Spectroscopy (UPS)
- Auger Electron Spectroscopy (AES)
- Low-energy He+ ion scattering (LEIS)
- Thermal Programmed Desorption Spectroscopy (TPD)
Team
Former Members
Publications
2024
Birschitzky, Viktor; Sokolovic, Igor; Prezzi, Michael; Palotas, Krisztian; Setvin, Martin; Diebold, Ulrike; Reticcioli, Michele; Franchini, Cesare
Machine learning-based prediction of polaron-vacancy patterns on the TiO2(110) surface
Journal ArticleOpen AccessIn: npj Computational Materials, vol. 10, no. 89, 2024.
Abstract | Links | BibTeX | Tags: P02, P07
@article{Birschitzky_2024a,
title = {Machine learning-based prediction of polaron-vacancy patterns on the TiO_{2}(110) surface},
author = {Viktor Birschitzky and Igor Sokolovic and Michael Prezzi and Krisztian Palotas and Martin Setvin and Ulrike Diebold and Michele Reticcioli and Cesare Franchini},
url = {https://www.nature.com/articles/s41524-024-01289-4},
doi = {https://doi.org/10.1038/s41524-024-01289-4},
year = {2024},
date = {2024-05-06},
urldate = {2024-05-06},
journal = {npj Computational Materials},
volume = {10},
number = {89},
abstract = {The multifaceted physics of oxides is shaped by their composition and the presence of defects, which are often accompanied by the formation of polarons. The simultaneous presence of polarons and defects, and their complex interactions, pose challenges for first-principles simulations and experimental techniques. In this study, we leverage machine learning and a first-principles database to analyze the distribution of surface oxygen vacancies (V_{O}) and induced small polarons on rutile TiO_{2}(110), effectively disentangling the interactions between polarons and defects. By combining neural-network supervised learning and simulated annealing, we elucidate the inhomogeneous VO distribution observed in scanning probe microscopy (SPM). Our approach allows us to understand and predict defective surface patterns at enhanced length scales, identifying the specific role of individual types of defects. Specifically, surface-polaron-stabilizing V_{O}-configurations are identified, which could have consequences for surface reactivity.},
keywords = {P02, P07},
pubstate = {published},
tppubtype = {article}
}
Celiberti, Lorenzo; Mosca, Dario Fiore; Allodi, Giuseppe; Pourovskii, Leonid V.; Tassetti, Anna; Forino, Paola Caterina; Cong, Rong; Garcia, Erick; Tran, Phuong M.; Renzi, Roberto De; Woodward, Patrick M.; Mitrović, Vesna F.; Sanna, Samuele; Franchini, Cesare
Spin-orbital Jahn-Teller bipolarons
Journal ArticleOpen AccessIn: Nature Communications, vol. 15, no. 2429, 2024.
Abstract | Links | BibTeX | Tags: P07
@article{Celiberti2024,
title = {Spin-orbital Jahn-Teller bipolarons},
author = {Lorenzo Celiberti and Dario Fiore Mosca and Giuseppe Allodi and Leonid V. Pourovskii and Anna Tassetti and Paola Caterina Forino and Rong Cong and Erick Garcia and Phuong M. Tran and Roberto De Renzi and Patrick M. Woodward and Vesna F. Mitrović and Samuele Sanna and Cesare Franchini},
url = {https://doi.org/10.1038/s41467-024-46621-0},
doi = {10.1038/s41467-024-46621-0},
year = {2024},
date = {2024-03-18},
urldate = {2024-03-18},
journal = {Nature Communications},
volume = {15},
number = {2429},
abstract = {Polarons and spin-orbit (SO) coupling are distinct quantum effects that play a critical role in charge transport and spin-orbitronics. Polarons originate from strong electron-phonon interaction and are ubiquitous in polarizable materials featuring electron localization, in particular 3d transition metal oxides (TMOs). On the other hand, the relativistic coupling between the spin and orbital angular momentum is notable in lattices with heavy atoms and develops in 5d TMOs, where electrons are spatially delocalized. Here we combine ab initio calculations and magnetic measurements to show that these two seemingly mutually exclusive interactions are entangled in the electron-doped SO-coupled Mott insulator Ba_{2}Na_{1−x}Ca_{x}OsO_{6} (0 < x < 1), unveiling the formation of spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller lattice activity, converts the Os 5d^{1} spin-orbital J_{eff} = 3/2 levels, characteristic of the parent compound Ba_{2}NaOsO_{6} (BNOO), into a bipolaron 5d^{2} J_{eff} = 2 manifold, leading to the coexistence of different J-effective states in a single-phase material. The gradual increase of bipolarons with increasing doping creates robust in-gap states that prevents the transition to a metal phase even at ultrahigh doping, thus preserving the Mott gap across the entire doping range from d^{1} BNOO to d^{2} Ba_{2}CaOsO_{6} (BCOO).},
keywords = {P07},
pubstate = {published},
tppubtype = {article}
}
Wang, Chunlei; Sombut, Panukorn; Puntscher, Lena; Jakub, Zdenek; Meier, Matthias; Pavelec, Jiri; Bliem, Roland; Schmid, Michael; Diebold, Ulrike; Franchini, Cesare; Parkinson, Gareth S.
CO‐Induced Dimer Decay Responsible for Gem‐Dicarbonyl Formation on a Model Single‐Atom Catalyst
Journal ArticleOpen AccessIn PressIn: Angewandte Chemie - International Edition, no. e202317347, 2024, ISSN: 1521-3773.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Wang2024,
title = {CO‐Induced Dimer Decay Responsible for Gem‐Dicarbonyl Formation on a Model Single‐Atom Catalyst},
author = {Chunlei Wang and Panukorn Sombut and Lena Puntscher and Zdenek Jakub and Matthias Meier and Jiri Pavelec and Roland Bliem and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},
doi = {10.1002/anie.202317347},
issn = {1521-3773},
year = {2024},
date = {2024-01-31},
journal = {Angewandte Chemie - International Edition},
number = {e202317347},
publisher = {Wiley},
abstract = {The ability to coordinate multiple reactants at the same active site is important for the wide-spread applicability of single-atom catalysis. Model catalysts are ideal to investigate the link between active site geometry and reactant binding, because the structure of single-crystal surfaces can be precisely determined, the adsorbates imaged by scanning tunneling microscopy (STM), and direct comparisons made to density functional theory. In this study, we follow the evolution of Rh_{1} adatoms and minority Rh_{2} dimers on Fe_{3}O_{4}(001) during exposure to CO using time-lapse STM at room temperature. CO adsorption at Rh_{1} sites results exclusively in stable Rh_{1}CO monocarbonyls, because the Rh atom adapts its coordination to create a stable pseudo-square planar environment. Rh_{1}(CO)_{2} gem-dicarbonyl species are also observed, but these form exclusively through the breakup of Rh_{2} dimers via an unstable Rh_{2}(CO)_{3} intermediate. Overall, our results illustrate how minority species invisible to area-averaging spectra can play an important role in catalytic systems, and show that the decomposition of dimers or small clusters can be an avenue to produce reactive, metastable configurations in single-atom catalysis.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}
2023
Puntscher, Lena; Sombut, Panukorn; Wang, Chunlei; Ulreich, Manuel; Pavelec, Jiri; Rafsanjani-Abbasi, Ali; Meier, Matthias; Lagin, Adam; Setvin, Martin; Diebold, Ulrike; Franchini, Cesare; Schmid, Michael; Parkinson, Gareth S.
A Multitechnique Study of C2H4 Adsorption on Fe3O4(001)
Journal ArticleOpen AccessIn: Journal of Physical Chemistry C, vol. 127, iss. 37, pp. 18378–18388, 2023.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Puntscher2023,
title = {A Multitechnique Study of C_{2}H_{4} Adsorption on Fe_{3}O_{4}(001)},
author = {Lena Puntscher and Panukorn Sombut and Chunlei Wang and Manuel Ulreich and Jiri Pavelec and Ali Rafsanjani-Abbasi and Matthias Meier and Adam Lagin and Martin Setvin and Ulrike Diebold and Cesare Franchini and Michael Schmid and Gareth S. Parkinson},
doi = {10.1021/acs.jpcc.3c03684},
year = {2023},
date = {2023-09-11},
urldate = {2023-09-11},
journal = {Journal of Physical Chemistry C},
volume = {127},
issue = {37},
pages = {18378--18388},
publisher = {American Chemical Society (ACS)},
abstract = {The adsorption/desorption of ethene (C_{2}H_{4}), also commonly known as ethylene, on Fe_{3}O_{4}(001) was studied under ultrahigh vacuum conditions using temperature-programmed desorption (TPD), scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT)-based computations. To interpret the TPD data, we have employed a new analysis method based on equilibrium thermodynamics. C_{2}H_{4} adsorbs intact at all coverages and interacts most strongly with surface defects such as antiphase domain boundaries and Fe adatoms. On the regular surface, C_{2}H_{4} binds atop surface Fe sites up to a coverage of 2 molecules per (√2 × √2)R45° unit cell, with every second Fe occupied. A desorption energy of 0.36 eV is determined by analysis of the TPD spectra at this coverage, which is approximately 0.1–0.2 eV lower than the value calculated by DFT + U with van der Waals corrections. Additional molecules are accommodated in between the Fe rows. These are stabilized by attractive interactions with the molecules adsorbed at Fe sites. The total capacity of the surface for C_{2}H_{4} adsorption is found to be close to 4 molecules per (√2 × √2)R45° unit cell.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}
Tresca, Cesare; Forcella, Pietro Maria; Angeletti, Andrea; Ranalli, Luigi; Franchini, Cesare; Reticcioli, Michele; Profeta, Gianni
Evidence of Molecular Hydrogen in the N-doped LuH3 System: a Possible Path to Superconductivity?
Journal ArticleSubmittedarXivIn: arXiv, 2023.
Abstract | Links | BibTeX | Tags: P07
@article{Tresca2024,
title = {Evidence of Molecular Hydrogen in the N-doped LuH3 System: a Possible Path to Superconductivity?},
author = {Cesare Tresca and Pietro Maria Forcella and Andrea Angeletti and Luigi Ranalli and Cesare Franchini and Michele Reticcioli and Gianni Profeta},
url = {https://arxiv.org/abs/2308.03619},
year = {2023},
date = {2023-08-07},
urldate = {2023-08-07},
journal = {arXiv},
abstract = {The report of near-ambient superconductivity in nitrogen-doped lutetium hydrides could represent an epochal discovery, awaited for more than a century, possibly leading to inconceivable scientific and technological implications. However, after months since the first report, clear experimental and theoretical confirmations are yet to come: The initially proposed compound structure fails to explain the superconducting behavior, calling for a shift in perspective. By means of machine-learning-accelerated force-field molecular dynamics, we explore the formation of H_{2} molecules in nitrogen-doped lutetium hydride, demonstrating the active role of nitrogen in stabilizing this phase. Our density functional theory calculations show that the presence of hydrogen molecules leads to a dynamically stable structure, characterized by a superconducting phase requiring no applied pressure, although the predicted temperatures are still much lower than room temperature. We believe that the possibility to stabilize hydrogen in molecular form represents a new route to explore disordered phases in hydrides and their transport properties at near ambient conditions.},
keywords = {P07},
pubstate = {published},
tppubtype = {article}
}
Redondo, Jesus; Reticcioli, Michele; Gabriel, Vit; Wrana, Dominik; Ellinger, Florian; Riva, Michele; Franceschi, Giada; Rheinfrank, Erik; Sokolovic, Igor; Jakub, Zdenek; Kraushofer, Florian; Alexander, Aji; Patera, Laerte L.; Repp, Jascha; Schmid, Michael; Diebold, Ulrike; Parkinson, Gareth S.; Franchini, Cesare; Kocan, Pavel; Setvin, Martin
Real-space investigation of polarons in hematite Fe2O3
Journal ArticleSubmittedarXivIn: arXiv, 2023.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Redondo2024,
title = {Real-space investigation of polarons in hematite Fe2O3},
author = {Jesus Redondo and Michele Reticcioli and Vit Gabriel and Dominik Wrana and Florian Ellinger and Michele Riva and Giada Franceschi and Erik Rheinfrank and Igor Sokolovic and Zdenek Jakub and Florian Kraushofer and Aji Alexander and Laerte L. Patera and Jascha Repp and Michael Schmid and Ulrike Diebold and Gareth S. Parkinson and Cesare Franchini and Pavel Kocan and Martin Setvin},
url = {https://arxiv.org/abs/2303.17945},
year = {2023},
date = {2023-03-31},
urldate = {2023-03-31},
journal = {arXiv},
abstract = {In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behaviour. The resulting polarons play a central role in many materials properties including electrical transport, optical properties, surface reactivity and magnetoresistance, and polaron properties are typically investigated indirectly through such macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in Fe_{2}O_{3} at the single quasiparticle limit. A combination of Kelvin probe force microscopy (KPFM) and kinetic Monte Carlo (KMC) simulations shows that Ti doping dramatically enhances the mobility of electron polarons, and density functional theory (DFT) calculations indicate that a metallic transition state is responsible for the enhancement. In contrast, hole polarons are significantly less mobile and their hopping is hampered further by the introduction of trapping centres.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}
Kraushofer, Florian; Meier, Matthias; Jakub, Zdeněk; Hütner, Johanna; Balajka, Jan; Hulva, Jan; Schmid, Michael; Franchini, Cesare; Diebold, Ulrike; Parkinson, Gareth S.
Oxygen-Terminated (1 × 1) Reconstruction of Reduced Magnetite Fe3O4(111)
Journal ArticleOpen AccessIn: vol. 14, no. 13, pp. 3258–3265, 2023.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Kraushofer2023,
title = {Oxygen-Terminated (1 × 1) Reconstruction of Reduced Magnetite Fe_{3}O_{4}(111)},
author = {Florian Kraushofer and Matthias Meier and Zdeněk Jakub and Johanna Hütner and Jan Balajka and Jan Hulva and Michael Schmid and Cesare Franchini and Ulrike Diebold and Gareth S. Parkinson},
doi = {10.1021/acs.jpclett.3c00281},
year = {2023},
date = {2023-03-28},
urldate = {2023-03-28},
volume = {14},
number = {13},
pages = {3258--3265},
publisher = {American Chemical Society (ACS)},
abstract = {The (111) facet of magnetite (Fe_{3}O_{4}) has been studied extensively by experimental and theoretical methods, but controversy remains regarding the structure of its low-energy surface terminations. Using density functional theory (DFT) computations, we demonstrate three reconstructions that are more favorable than the accepted Feoct2 termination under reducing conditions. All three structures change the coordination of iron in the kagome Feoct1 layer to be tetrahedral. With atomically resolved microscopy techniques, we show that the termination that coexists with the Fetet1 termination consists of tetrahedral iron capped by 3-fold coordinated oxygen atoms. This structure explains the inert nature of the reduced patches.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}
Verdi, Carla; Ranalli, Luigi; Franchini, Cesare; Kresse, Georg
Journal ArticleIn: Physical Review Materials, vol. 7, no. 3, pp. l030801, 2023.
Abstract | Links | BibTeX | Tags: P03, P07
@article{Verdi2023,
title = {Quantum paraelectricity and structural phase transitions in strontium titanate beyond density functional theory},
author = {Carla Verdi and Luigi Ranalli and Cesare Franchini and Georg Kresse},
doi = {10.1103/physrevmaterials.7.l030801},
year = {2023},
date = {2023-03-16},
journal = {Physical Review Materials},
volume = {7},
number = {3},
pages = {l030801},
publisher = {American Physical Society (APS)},
abstract = {We demonstrate an approach for calculating temperature-dependent quantum and anharmonic effects with beyond density-functional theory accuracy. By combining machine-learned potentials and the stochastic self-consistent harmonic approximation, we investigate the cubic to tetragonal transition in strontium titanate and show that the paraelectric phase is stabilized by anharmonic quantum fluctuations. We find that a quantitative understanding of the quantum paraelectric behavior requires a higher-level treatment of electronic correlation effects via the random phase approximation. This approach enables detailed studies of emergent properties in strongly anharmonic materials beyond density-functional theory.},
keywords = {P03, P07},
pubstate = {published},
tppubtype = {article}
}
Ranalli, Luigi; Verdi, Carla; Monacelli, Lorenzo; Kresse, Georg; Calandra, Matteo; Franchini, Cesare
Journal ArticleOpen AccessIn: Advanced Quantum Technology, vol. 6, iss. 4, 2023.
Abstract | Links | BibTeX | Tags: P03, P07
@article{Ranalli2023,
title = {Temperature-dependent anharmonic phonons in quantum paraelectric KTaO_{3} by first principles and machine-learned force fields},
author = {Luigi Ranalli and Carla Verdi and Lorenzo Monacelli and Georg Kresse and Matteo Calandra and Cesare Franchini},
doi = {10.1002/qute.202200131},
year = {2023},
date = {2023-02-22},
urldate = {2023-02-22},
journal = {Advanced Quantum Technology},
volume = {6},
issue = {4},
abstract = {Understanding collective phenomena in quantum materials from first principles is a promising route toward engineering materials properties and designing new functionalities. This work examines the quantum paraelectric state, an elusive state of matter characterized by the smooth saturation of the ferroelectric instability at low temperature due to quantum fluctuations associated with anharmonic phonon effects. The temperature-dependent evolution of the soft ferroelectric phonon mode in the quantum paraelectric KTaO_{3} in the range 0–300 K is modeled by combining density functional theory (DFT) calculations with the stochastic self-consistent harmonic approximation assisted by an on-the-fly machine-learned force field. The calculated data show that including anharmonic terms is essential to stabilize the spurious imaginary ferroelectric phonon predicted by DFT in the harmonic approximation, in agreement with experiments. Augmenting the DFT workflow with machine-learned force fields allows for efficient stochastic sampling of the configuration space using large supercells in a wide temperature range, inaccessible to conventional ab initio protocols. This work proposes a robust computational workflow capable of accounting for collective behaviors involving different degrees of freedom and occurring at large time/length scales, paving the way for precise modeling and control of quantum effects in materials.},
keywords = {P03, P07},
pubstate = {published},
tppubtype = {article}
}
Corrias, Marco; Papa, Lorenzo; Sokolovíc, Igor; Birschitzky, Viktor; Gorfer, Alexander; Setvin, Martin; Schmid, Michael; Diebold, Ulrike; Reticcioli, Michele; Franchini, Cesare
Automated Real-Space Lattice Extraction for Atomic Force Microscopy Images
Journal ArticleOpen AccessIn: Machine Learning: Science and Technology, vol. 4, pp. 015015, 2023.
Abstract | Links | BibTeX | Tags: P02, P07
@article{Corrias2023,
title = {Automated Real-Space Lattice Extraction for Atomic Force Microscopy Images},
author = {Marco Corrias and Lorenzo Papa and Igor Sokolovíc and Viktor Birschitzky and Alexander Gorfer and Martin Setvin and Michael Schmid and Ulrike Diebold and Michele Reticcioli and Cesare Franchini},
doi = {10.1088/2632-2153/acb5e0},
year = {2023},
date = {2023-01-24},
urldate = {2023-01-24},
journal = {Machine Learning: Science and Technology},
volume = {4},
pages = {015015},
abstract = {Analyzing atomically resolved images is a time-consuming process requiring solid experience and substantial human intervention. In addition, the acquired images contain a large amount of information such as crystal structure, presence and distribution of defects, and formation of domains, which need to be resolved to understand a material's surface structure. Therefore, machine learning techniques have been applied in scanning probe and electron microscopies during the last years, aiming for automatized and efficient image analysis. This work introduces a free and open source tool (AiSurf: Automated Identification of Surface Images) developed to inspect atomically resolved images via Scale-Invariant Feature Transform (SIFT) and Clustering Algorithms (CA). AiSurf extracts primitive lattice vectors, unit cells, and structural distortions from the original image, with no pre-assumption on the lattice and minimal user intervention. The method is applied to various atomically resolved non-contact atomic force microscopy (AFM) images of selected surfaces with different levels of complexity: anatase TiO_{2}(101), oxygen deficient rutile TiO_{2}(110) with and without CO adsorbates, SrTiO_{3}(001) with Sr vacancies and graphene with C vacancies. The code delivers excellent results and is tested against atom misclassification and artifacts, thereby facilitating the interpretation of scanning probe microscopy images.},
keywords = {P02, P07},
pubstate = {published},
tppubtype = {article}
}