Surface structure and reactivity of
multi-component oxides at the atomic scale

@article{ACSMEASURE2022,

title = {Why and How Savitzky–Golay Filters Should Be Replaced},

author = {Michael Schmid and David Rath and Ulrike Diebold},

url = {https://pubs.acs.org/doi/10.1021/acsmeasuresciau.1c00054},

doi = {10.1021/acsmeasuresciau.1c00054},

year  = {2022},

date = {2022-02-17},

urldate = {2022-02-17},

journal = {ACS Measurement Science Au},

volume = {2},

number = {2},

pages = {185--196},

abstract = {Savitzky–Golay (SG) filtering, based on local least-squares fitting of the data by polynomials, is a popular method for smoothing data and calculations of derivatives of noisy data. At frequencies above the cutoff, SG filters have poor noise suppression; this unnecessarily reduces the signal-to-noise ratio, especially when calculating derivatives of the data. In addition, SG filtering near the boundaries of the data range is prone to artifacts, which are especially strong when using SG filters for calculating derivatives of the data. We show how these disadvantages can be avoided while keeping the advantageous properties of SG filters. We present two classes of finite impulse response (FIR) filters with substantially improved frequency response: (i) SG filters with fitting weights in the shape of a window function and (ii) convolution kernels based on the sinc function with a Gaussian-like window function and additional corrections for improving the frequency response in the passband (modified sinc kernel). Compared with standard SG filters, the only price to pay for the improvement is a moderate increase in the kernel size. Smoothing at the boundaries of the data can be improved with a non-FIR method, the Whittaker–Henderson smoother, or by linear extrapolation of the data, followed by convolution with a modified sinc kernel, and we show that the latter is preferable in most cases. We provide computer programs and equations for the smoothing parameters of these smoothers when used as plug-in replacements for SG filters and describe how to choose smoothing parameters to preserve peak heights in spectra.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Franceschi2021,

title = {Two-dimensional surface phase diagram of a multicomponent perovskite oxide: La_{0.8}Sr_{0.2}MnO_{3} (110)},

author = {Giada Franceschi and Michael Schmid and Ulrike Diebold and Michele Riva},

doi = {10.1103/physrevmaterials.5.l092401},

year  = {2021},

date = {2021-09-24},

urldate = {2021-09-24},

journal = {Physical Review Materials},

volume = {5},

number = {9},

pages = {L092401},

publisher = {American Physical Society (APS)},

abstract = {The many surface reconstructions of (110)-oriented lanthanum strontium manganite (\textbf{La_{0.8}Sr_{0.2}MnO}3}}, LSMO) were followed as a function of the oxygen chemical potential (\textit{\textbf{μ}_{O}}) and the surface cation composition. Decreasing \textit{\textbf{μ}_{O}} causes Mn to migrate across the surface, enforcing phase separation into \textit{\textbf{A}}-site-rich areas and a variety of composition-related, structurally diverse \textit{\textbf{B}}-site-rich reconstructions. The composition of these phase-separated structures was quantified with scanning tunneling microscopy, and these results were used to build a two-dimensional phase diagram of the LSMO(110) equilibrium surface structures.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Mirabella2021,

title = {Ni-modified Fe_{3}O_{4}(001) surface as a simple model system for understanding the oxygen evolution reaction},

author = {Francesca Mirabella and Matthias Müllner and Thomas Touzalin and Michele Riva and Zdenek Jakub and Florian Kraushofer and Michael Schmid and Marc T M Koper and Gareth S. Parkinson and Ulrike Diebold},

doi = {10.1016/j.electacta.2021.138638},

year  = {2021},

date = {2021-09-01},

urldate = {2021-09-01},

journal = {Electrochimica Acta},

volume = {389},

pages = {138638},

publisher = {Elsevier BV},

abstract = {Electrochemical water splitting is an environmentally friendly technology to store renewable energy in the form of chemical fuels. Among the earth-abundant first-row transition metal-based catalysts, mixed Ni-Fe oxides have shown promising performance for effective and low-cost catalysis of the oxygen evolution reaction (OER) in alkaline media, but the synergistic roles of Fe and Ni cations in the OER mechanism remain unclear. In this work, we report how addition of Ni changes the reactivity of a model iron oxide catalyst, based on Ni deposited on and incorporated in a magnetite Fe_{3}O_{4}(001) single crystal, using a combination of surface science techniques in ultra-high vacuum such as low energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and scanning tunneling microscopy (STM), as well as atomic force microscopy (AFM) in air, and electrochemical methods such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in alkaline media. A significant improvement in the OER activity is observed when the top surface presents an iron fraction among the cations in the range of 20-40%, which is in good agreement with what has been observed for powder catalysts. Furthermore, a decrease in the OER overpotential is observed following surface aging in electrolyte for three days. At higher Ni load, AFM shows the growth of a new phase attributed to an (oxy)-hydroxide phase which, according to CV measurements, does not seem to correlate with the surface activity towards OER. EIS suggests that the OER precursor species observed on the clean and Ni-modified surfaces are similar and Fe-centered, but form at lower overpotentials when the surface Fe:Ni ratio is optimized. We propose that the well-defined Fe_{3}O_{4}(001) surface can serve as a model system for understanding the OER mechanism and establishing the structure-reactivity relation on mixed Fe-Ni oxides.},

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

pubstate = {published},

tppubtype = {article}

}

@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{Timmermann2020,

title = {IrO_{2} Surface Complexions Identified through Machine Learning and Surface Investigations},

author = {Jakob Timmermann and Florian Kraushofer and Nikolaus Resch and Peigang Li and Yu Wang and Zhiqiang Mao and Michele Riva and Yonghyuk Lee and Carsten Staacke and Michael Schmid and Christoph Scheurer and Gareth S. Parkinson and Ulrike Diebold and Karsten Reuter},

doi = {10.1103/physrevlett.125.206101},

year  = {2020},

date = {2020-11-10},

urldate = {2020-11-10},

journal = {Physical Review Letters},

volume = {125},

number = {20},

pages = {206101},

publisher = {American Physical Society (APS)},

abstract = {A Gaussian approximation potential was trained using density-functional theory data to enable a global geometry optimization of low-index rutile IrO_{2} facets through simulated annealing. Ab initio thermodynamics identifies (101) and (111) (1×1) terminations competitive with (110) in reducing environments. Experiments on single crystals find that (101) facets dominate and exhibit the theoretically predicted (1×1) periodicity and x-ray photoelectron spectroscopy core-level shifts. The obtained structures are analogous to the complexions discussed in the context of ceramic battery materials.},

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

pubstate = {published},

tppubtype = {article}

}

@article{Franceschi2020,

title = {Atomically resolved surface phases of La_{0.8}Sr_{0.2}MnO_{3}(110) thin films},

author = {Giada Franceschi and Michael Schmid and Ulrike Diebold and Michele Riva},

doi = {10.1039/d0ta07032g},

year  = {2020},

date = {2020-09-04},

urldate = {2020-09-04},

journal = {Journal of Materials Chemistry A},

volume = {8},

number = {43},

pages = {22947--22961},

publisher = {Royal Society of Chemistry (RSC)},

abstract = {The atomic-scale properties of lanthanum–strontium manganite (La_{1-x}Sr_{x}MnO_{3−δ}, LSMO) surfaces are of high interest because of the roles of the material as a prototypical complex oxide, in the fabrication of spintronic devices and in catalytic applications. This work combines pulsed laser deposition (PLD) with atomically resolved scanning tunneling microscopy (STM) and surface analysis techniques (low-energy electron diffraction – LEED, X-ray photoelectron spectroscopy – XPS, and low-energy He^{+} ion scattering – LEIS) to assess the atomic properties of La_{0.8}Sr_{0.2}MnO_{3}(110) surfaces and their dependence on the surface composition. Epitaxial films with 130 nm thickness were grown on Nb-doped SrTiO_{3}(110) and their near-surface stoichiometry was adjusted by depositing La and Mn in sub-monolayer amounts, quantified with a movable quartz-crystal microbalance. The resulting surfaces were equilibrated at 700 °C under 0.2 mbar O_{2}, i.e., under conditions that bridge the gap between ultra-high vacuum and the operating conditions of high-temperature solid-oxide fuel cells, where LSMO is used as the cathode. The atomic details of various composition-related surface phases have been unveiled. The phases are characterized by distinct structural and electronic properties and vary in their ability to ccommodate deposited cations.},

keywords = {P02, pre-TACO},

pubstate = {published},

tppubtype = {article}

}

@article{Grumelli2020,

title = {Electrochemical Stability of the Reconstructed Fe_{3}O_{4}(001) Surface},

author = {Doris Grumelli and Tim Wiegmann and Sara Barja and Finn Reikowski and Fouad Maroun and Philippe Allongue and Jan Balajka and Gareth S. Parkinson and Ulrike Diebold and Klaus Kern and Olaf M Magnussen},

doi = {10.1002/anie.202008785},

year  = {2020},

date = {2020-07-29},

urldate = {2020-07-29},

journal = {Angewandte Chemie - International Edition},

volume = {59},

number = {49},

pages = {21904--21908},

publisher = {Wiley},

abstract = {Establishing the atomic-scale structure of metal-oxide surfaces during electrochemical reactions is a key step to modeling this important class of electrocatalysts. Here, we demonstrate that the characteristic (√2×√2)R45° surface reconstruction formed on (001)-oriented magnetite single crystals is maintained after immersion in 0.1 M NaOH at 0.20 V vs. Ag/AgCl and we investigate its dependence on the electrode potential. We follow the evolution of the surface using in situ and operando surface X-ray diffraction from the onset of hydrogen evolution, to potentials deep in the oxygen evolution reaction (OER) regime. The reconstruction remains stable for hours between −0.20 and 0.60 V and, surprisingly, is still present at anodic current densities of up to 10 mA cm^{−2} and strongly affects the OER kinetics. We attribute this to a stabilization of the Fe_{3}O_{4} bulk by the reconstructed surface. At more negative potentials, a gradual and largely irreversible lifting of the reconstruction is observed due to the onset of oxide reduction.},

keywords = {P02, P04, 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{Diebold2019,

title = {Preface: Surface Science of functional oxides},

author = {Ulrike Diebold and Günther Rupprechter},

doi = {10.1016/j.susc.2018.11.017},

year  = {2019},

date = {2019-03-01},

journal = {Surface Science},

volume = {681},

pages = {A1},

publisher = {Elsevier BV},

keywords = {P02, P08, pre-TACO},

pubstate = {published},

tppubtype = {article}

}