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

@article{Larsson_2026a,

title = {Platinum surface oxides govern the cathodic overpotential of the oxygen reduction reaction},

author = {Alfred Larsson and Andrea Grespi and Ozbej Vodeb and Karen van den Akker and Auden Ti and Claire Berschauer and Alexandra M. Imre and Philip Miguel Kofoed and Estephania Lira and Mahesh Ramakrishnan and Stuart Ansell and Justus Just and Henrik Grönbeck and Ulrike Diebold and Edvin Lundgren and Lindsay R. Merte and Dusan Strmcnik and Rik Moma and Marc T. M. Koper},

doi = {10.1039/D6EY00014B},

year  = {2026},

date = {2026-03-18},

journal = {EES Catalysis},

abstract = {The oxygen reduction reaction (ORR) on platinum is limited by a substantial overpotential, which hampers the efficiency of fuel cell technologies. While adsorbate binding energies have been widely used to explain ORR kinetics, we here illustrate a more complex role of platinum surface oxides, which are often ambiguously defined in the literature. We use operando total reflection X-ray absorption fine structure spectroscopy (RefleXAFS), supported by X-ray photoelectron spectroscopy, density functional theory, and microkinetic modeling, to resolve the surface oxides on polycrystalline platinum and their impact on ORR. We identify the formation of a surface oxide as early as 1 V_{RHE} in 0.1 M HClO_{4} and demonstrate that platinum spontaneously oxidizes at the open-circuit potential (OCP) under O_{2} saturation. Furthermore, we show that the oxide coverage increases with upper vertex potential, slower scan rates, and extended hold times at OCP, illustrating how oxides inhibit ORR during fuel cell start-up. Crucially, we demonstrate that the ORR onset is delayed until these oxides are reduced, establishing a direct, negative relationship between oxide coverage and ORR activity. This reveals a revised mechanism in which the potential-determining step is the reduction of surface oxides, and the slow kinetics of this restructuring ultimately determine when surface sites become catalytically available.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Takezawa_2026a,

title = {Initial Growth Process of Cu Thin Films on bcc-FeCo/MgO(100) via Molecular Beam Epitaxy},

author = {Shingo Takezawa and Michele Riva and Florian Dörr and Michael Schmid and Taisuke Sasaki and Takanobu Hiroto and Masato Kotsugi and Koichiro Yaji and Yuya Sakuraba and Naoka Nagamura},

doi = {10.1380/ejssnt.2026-004},

year  = {2026},

date = {2026-02-26},

urldate = {2026-02-26},

journal = {e-Journal of Surface Science and Nanotechnology},

volume = {24},

number = {1},

pages = {21-25},

abstract = {We investigated the thickness-dependent structural evolution of Cu/FeCo(100) thin films grown by molecular beam epitaxy (MBE). At the initial stage of growth, Cu adopted a body-centered cubic (bcc) structure templated by the underlying FeCo substrate. Once the Cu thickness exceeded approximately 3 nm, a structural transformation into the face-centered cubic (fcc) phase was observed. The MBE-grown films exhibited interfacial dislocations and developed a disordered surface in the thickness range of 3–5 nm. Although metastable ultrathin bcc-Cu films on FeCo(100) grown by MBE are less stable than sputtered multilayers, MBE offers a unique advantage: it enables in-situ advanced characterization such as angle-resolved photoemission spectroscopy (ARPES) in the ultrathin regime around 1 nm. This capability is essential for designing high-performance devices and probing interface-driven electronic phenomena.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Imre_2026a,

title = {An improved reliability factor for quantitative low-energy electron diffraction},

author = {Alexandra M. Imre and Lutz Hammer and Ulrike Diebold and Michele Riva and Michael Schmid},

doi = {10.1088/1361-648X/ae4af8},

year  = {2026},

date = {2026-02-26},

journal = {Journal of Physics: Condensed Matter},

abstract = {Quantitative low-energy electron diffraction [LEED I(V) or LEED I(E)], which evaluates the diffraction intensities I as a function of the electron energy, is a versatile technique for the study of surface structures. The technique is based on optimizing the agreement between experimental and calculated intensities. Today, the most commonly used measure of agreement is Pendry's R_{P}. While R_{P} has many advantages it also has severe shortcomings, as it is a noisy target function for optimization and very sensitive to small offsets of the intensity. Furthermore, R_{P} = 0, which is meant to imply perfect agreement between two I(E) curves, can also be achieved by qualitatively very different curves. We present a modified R_{S}, which can be used as a direct replacement for R_{P}, but avoids these shortcomings. We also demonstrate that R_{S} is as good as R_{P} or better in steering the optimization to the correct result in the case of imperfections in the experimental data, while another common R factor, R_{ZJ} (suggested by Zanazzi and Jona) is worse in this respect.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Wang_2026a,

title = {Hydrogen Activation via Dihydride Formation on a Rh_{1}/Fe_{3}O_{4}(001) Single-Atom Catalyst},

author = {Chunlei Wang and Panukorn Sombut and Lena Puntscher and Nail Barama and Maosheng Hao and Florian Kraushofer and Jiri Pavelec and Matthias Meier and Florian Libisch and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},

doi = {10.1002/anie.202525745},

year  = {2026},

date = {2026-02-18},

urldate = {2026-02-18},

journal = {Angewandte Chemie International Edition},

pages = {e25745},

abstract = {Hydrogen activation is a key elementary step in catalytic hydrogenation. In heterogeneous catalysis, it usually proceeds through dissociative adsorption on metal nanoparticles followed by surface diffusion or spillover, whereas homogeneous catalysts activate H_{2} through dihydride or dihydrogen intermediates at a single metal center. Here, we show that isolated Rh adatoms supported on Fe_{3}O_{4}(001) activate hydrogen through formation of a stable dihydride species without atomic H spillover. Temperature-programmed desorption, x-ray photoelectron spectroscopy, and scanning tunneling microscopy collectively reveal strong (≈1 eV) hydrogen adsorption exclusively at isolated Rh_{1} sites, while isotope-exchange experiments further demonstrate that hydrogen remains localized. Density-functional theory-based calculations indicate a barrierless conversion from molecular H_{2} to the dihydride, and random-phase approximation calculations further confirm the relative stability of the dihydride. Together, these results show that single-atom Rh sites cleave hydrogen through a dihydride pathway analogous to homogeneous complexes, establishing a mechanistic bridge between homogeneous and heterogeneous catalysis.},

keywords = {P02, P04, P07},

pubstate = {published},

tppubtype = {article}

}

@article{Wadhwa_2025a,

title = {Machine learning study of surface reconstructions of the Cu_{2}⁢O⁡(111) surface},

author = {Payal Wadhwa and Michael Schmid and Georg Kresse},

doi = {10.1103/sfjm-1gyr},

year  = {2025},

date = {2025-11-17},

journal = {Physical Review B},

volume = {112},

issue = {20},

pages = {205420},

abstract = {The atomic structure of the most stable reconstructed surface of cuprous oxide (Cu_{2}⁢O)⁢(111) surface has been a longstanding topic of debate. In this study, we develop on-the-fly machine-learned force fields (MLFFs) to systematically investigate the various reconstructions of the Cu_{2}⁢O⁡(111) surface under stoichiometric as well as O- and Cu-deficient or rich conditions, focusing on both (√3×√3⁢)R⁢30∘ and (2×2) supercells. By utilizing parallel tempering simulations supported by MLFFs, we confirm that the previously described nanopyramidal and Cu-deficient (1×1) structures are the lowest energy structures from moderately to strongly oxidizing conditions. In addition, we identify two promising nanopyramidal reconstructions at highly reducing conditions, a stoichiometric one and a Cu-rich one. Surface energy calculations performed using spin-polarized PBE, PBE+𝑈, r2⁢SCAN, and HSE06 functionals show that the previously known Cu-deficient configuration and nanopyramidal configurations are at the convex hull (and, thus, equilibrium structures) for all functionals, whereas the stability of the other structures depends on the functional and is therefore uncertain. Our findings demonstrate that on-the-fly trained MLFFs provide a simple, efficient, and rapid approach to explore the complex surface reconstructions commonly encountered in experimental studies, and also enhance our understanding of the stability of Cu_{2}⁢O⁡(111) surfaces.},

keywords = {P02, P03},

pubstate = {published},

tppubtype = {article}

}

@article{Huetner_2025a,

title = {Surface reconstructions govern ice nucleation on silver iodide},

author = {Johanna I. Hütner and Andrea Conti and David Kugler and Franziska Sabath and Kim Noelle Dreier and Hans-Georg Stammler and Florian Mittendorfer and Angelika Kühnle and Michael Schmid and Ulrike Diebold and Jan Balajka},

doi = {10.1126/sciadv.aea2378},

year  = {2025},

date = {2025-10-31},

journal = {Science Advances},

volume = {11},

number = {44},

pages = {eaea2378},

abstract = {Silver iodide (AgI) is among the most effective ice-nucleating agents, attributed to its close lattice match with hexagonal ice. However, the atomic-level mechanism behind its efficiency remains unclear. The basal surfaces of AgI are polar and inherently unstable, necessitating a compensation mechanism, such as surface reconstruction, which may disrupt the favorable lattice match with ice. We combine noncontact atomic force microscopy with advanced computational modeling to determine the atomic structure of basal AgI surfaces in ultrahigh vacuum. The Ag-terminated (0001) surface exhibits a (2 × 2) reconstruction with ordered Ag vacancies, preserving a hexagonal arrangement of surface atoms that facilitates epitaxial ice growth. In contrast, the I-terminated (0001) surface adopts a complex rectangular reconstruction, incompatible with continuous ice layer formation. These findings highlight the decisive role of surface atomic structure and indicate that the Ag-terminated basal plane is primarily responsible for efficient ice nucleation on AgI.},

keywords = {P02, P04},

pubstate = {published},

tppubtype = {article}

}

@article{Eder_2025a,

title = {Multi-technique characterization of rhodium gem-dicarbonyls on TiO_{2}(110)},

author = {Moritz Eder and Faith J. Lewis and Johanna I. Hütner and Panukorn Sombut and Maosheng Hao and David Rath and Paul Ryan and Jan Balajka and Margareta Wagner and Matthias Meier and Cesare Franchini and Gianfranco Pacchioni and Ulrike Diebold and Michael Schmid and Florian Libisch and Jiři Pavelec and Gareth S. Parkinson},

doi = {10.1039/D5SC04889C},

year  = {2025},

date = {2025-10-16},

journal = {Chemical Science},

abstract = {Gem-dicarbonyls of transition metals supported on metal (oxide) surfaces are common intermediates in heterogeneous catalysis. While infrared (IR) spectroscopy is a standard tool for detecting these species on powder catalysts, the ill-defined crystallographic environment renders data interpretation challenging. In this work, we apply a multi-technique surface science approach to investigate rhodium gem-dicarbonyls on a single-crystalline rutile TiO_{2}(110) surface. We combine spectroscopy, scanning probe microscopy, and density functional theory (DFT) to determine their location and coordination on the surface. IR spectroscopy shows the successful creation of gem-dicarbonyls on a titania single crystal by exposing deposited Rh atoms to CO gas, followed by annealing to 200–250 K. Low-temperature scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) data reveal that these complexes are mostly aligned along the [001] crystallographic direction, corroborating theoretical predictions. Notably, X-ray photoelectron spectroscopy (XPS) data reveal multiple rhodium species on the surface, even when the IR spectra show only the signature of rhodium gem-dicarbonyls. As such, our results highlight the complex behavior of carbonyls on metal oxide surfaces, and demonstrate the necessity of multi-technique approaches for the adequate characterization of single-atom catalysts.},

keywords = {P02, P04, P07},

pubstate = {published},

tppubtype = {article}

}

@article{Sokolovic_2025a,

title = {Duality and degeneracy lifting in two-dimensional electron liquids on SrTiO_{3}(001)},

author = {Igor Sokolović and Eduardo B. Guedes and Thomas P. van Waas and Fei Guo and Samuel Poncé and Craig Polley and Michael Schmid and Ulrike Diebold and Milan Radović and Martin Setvín and J. Hugo Dil},

url = {https://doi.org/10.1038/s41467-025-59258-4},

year  = {2025},

date = {2025-05-17},

journal = {Nature Communications},

volume = {16},

issue = {1},

pages = {4594},

abstract = {Two-dimensional electron liquids (2DELs) have increasing technological relevance for ultrafast electronics and spintronics, yet significant gaps in their fundamental understanding are exemplified on the prototypical SrTiO_{3}. We correlate the exact SrTiO_{3}(001) surface structure with distinct 2DELs through combined microscopic angle-resolved photoemission spectroscopy and non-contact atomic force microscopy on truly bulk-terminated surfaces that alleviate structural uncertainties inherent to this long-studied system. The SrO termination is shown to develop a 2DEL following the creation of oxygen vacancies, unlike the intrinsically metallic TiO_{2} termination. Differences in degeneracy of the 2DELs, with nearly the same band filling and identical band bending, are assigned to polar distortions of the Ti atoms in combination with spin order, supported with the extraction of fundamental electron-phonon coupling strength. These results not only resolve the ambiguities regarding 2DELs on SrTiO_{3} thus far, but also pave the way to manipulating band filling and spin order in oxide 2DELs in general.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}

@article{Sokolovic_2024a,

title = {How to cleave cubic perovskite oxides},

author = {Igor Sokolović and Michael Schmid and Ulrike Diebold and Martin Setvín},

doi = {10.1063/5.0233747},

year  = {2025},

date = {2025-03-20},

urldate = {2025-03-20},

journal = {Review of Scientific Instruments},

volume = {96},

issue = {3},

pages = {035113},

abstract = {Surfaces of cubic perovskite oxides attract significant attention for their physical tunability and high potential for technical applications. Bulk-terminated surfaces are desirable for theoretical modeling and experimental reproducibility, yet there is a lack of methods for preparing such well-defined surfaces. We discuss a method for strain-assisted cleaving of perovskite single crystals, using a setup easily transferable between different experimental systems. The details of the cleaving device and the procedure were optimized in a systematic study on the model cubic perovskite oxide SrTiO_{3}. The large-area morphology and typical distribution of surface terminations on cleaved SrTiO_{3}(001) are presented, with specific guidelines on how to distinguish well-cleaved surfaces from conchoidally fractured ones. The cleaving is applicable to other cubic perovskites, as demonstrated on KTaO_{3}(001) and BaTiO_{3}(001). This approach opens up a pathway for obtaining high-quality surfaces of this promising class of materials.},

keywords = {P02},

pubstate = {published},

tppubtype = {article}

}