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In this study, we investigated the atomic-level interaction between CO molecules and a well-ordered Mn3O4(001) thin film. The oxide film, initially grown on a single-crystal Au(111) substrate, was characterized using X-ray photoelectron spectroscopy (XPS) to determine its oxidation state. Further examination of the film structure through scanning transmission electron microscopy (STEM) and low-energy electron diffraction (LEED) revealed its growth orientation along the [001] direction, with three domains rotated by 60° and aligned with the ⟨110⟩Audirections. Notably, the termination of the film features a layer of Mn3+cations covered with oxygen atoms. The study then focused on the interaction of the film with CO, employing infrared reflection absorption spectroscopy (IRAS) and temperature-programmed IRAS (TP-IRAS). The results unveiled two distinct IR peaks related to CO adsorption: one at 2140 cm–1, signifying that CO molecules weakly adsorbed on the oxygen-terminated surface of Mn3+cations, and another at 2105 cm–1, indicative of CO molecules bound to Mn2+cations at oxygen vacancies.

We investigated the electronic and the structural properties of Mn3O4thin films grown on Cu(111) as a function of preparation conditions (oxygen partial pressure and thickness). Mn3O4films are grown at oxygen partial pressure of 5 × 10–7mbar and displayed a (110) preferential plane orientation arranged in different spatial domains to better adapt to Cu(111) lattice parameters. The relative angle between the domains varies as the film thickness increases. At the Mn3O4/Cu(111) interface, the valence band is strongly perturbed by the contribution of Cu 3d states that modify the Mn 3d electronic configuration. As a consequence, Mn 3s and Mn 2p core level spectra present characteristic new line shapes that were explained within the core-level relaxation framework. At variance with other metal substrates used for stabilizing manganese oxides thin films, the copper presents a 3d electronic distribution strongly overlapping the Mn 3d orbital and consequently affecting the overall electronic properties at the contact layer.

We studied the adsorption and thermal behavior of the nitrile-functionalized ionic liquid (IL) [C3CNC1Im][Tf2N] on Au(111) and Pt(111) between 150 and 600 K. Ultrathin films were prepared at 150 K by physical vapor deposition (PVD) and were characterized by angle resolved X-ray photoelectron spectroscopy (ARXPS). At 150 K, the IL adsorbs intact with a similar orientation on both surfaces: In the first layer, the so-called wetting layer, the cation lies flat on the surface and the anion is bound in cis-configuration with the SO2groups toward the surface and the CF3groups away from the surface. On Au(111), subsequent deposition of IL in the multilayer regime at 150 K shows 2D growth up until ∼0.75 ML and a transition to moderate 3D at higher coverages. Temperature-programmed XPS indicates a change in surface morphology toward more pronounced 3D islands for the multilayers on top of the wetting layer between 220 and 290 K. From 350 to 440 K, desorption of multilayers occurs, with IL decomposition starting at 375–400 K. On the more reactive Pt(111) surface, decomposition starts already above 280 K. Notably, this temperature is ∼80 K higher than the onset for decomposition of related nonfunctionalized imidazolium-based ILs, that is, [C2C1Im][OTf], [C1C1Im][Tf2N], and [C8C1Im][Tf2N] on Pt(111). This difference is attributed to the nitrile functionality. Our findings demonstrate that functionalizing ILs significantly modifies their thermal properties, which is of high relevance for SCILL (solid catalyst with an ionic liquid layer) systems.

The correlation between the geometric structure and reactivity of an oxide surface is crucial to designing new catalytic materials. This work uses a well-ordered Mn3O4(001) thin film phase to investigate water-oxide interaction. Based on scanning tunneling microscopy data, we propose that water molecule adsorption occurs at oxygen-defective sites and is followed by water dissociation. The vibrational modes related to the D2O (heavy water) physisorbed and the chemisorbed OsD on the surface were identified by infrared reflection absorption spectroscopy at the cryogenic temperature range. Photoelectron spectroscopy at near ambient pressure shows that the water adsorption at defective sites reaches a saturation condition. For water pressures lower than 1 × 10–4mbar, the crystalline structure of the Mn3O4(001) thin film is preserved. Temperature-programmed spectroscopy probed the desorption process and showed that the water interaction induces a phase transition from Mn3O4to MnO.

The concept of a solid catalyst with an ionic liquid layer (SCILL) is a promising approach to improve the selectivity of noble metal catalysts in heterogeneous reactions. In order to understand the origins of this selectivity control, we investigated the growth and thermal stability of ultrathin 1-ethyl-3-methylimidazolium trifluormethanesulfonate [C2C1Im][OTf] films on Pt(111) by infrared reflection absorption spectroscopy (IRAS) and X-ray photoelectron spectroscopy (XPS) in time-resolved and temperature-programmed experiments. We combined these spectroscopy experiments with scanning tunneling microscopy (STM) to obtain detailed insights into the orientation and adsorption geometry of the ions in the first IL layer. Furthermore, we propose a mechanism for the thermal evolution of [C2C1Im][OTf] on Pt(111). We observe an intact IL layer on the surface at temperatures below 200 K. Adsorbed [C2C1Im][OTf] forms islands, which are evenly distributed over the surface. The [OTf]-anion adsorbs via the SO3group, with the molecular axis perpendicular to the surface. Anions and cations are arranged next to each other, alternating on the Pt(111) surface. Upon heating to 250 K, we observe changes in geometry and structural distribution. Whereas at low temperature, the ions are arranged alternately for electrostatic reasons, this driving force is no longer decisive at 250 K. Here, a phase separation of two different species is discernible in STM. We propose that this effect is due to a surface reaction, which changes the charge of the adsorbates. We assume that the IL starts to decompose at around 250 K, and thus, pristine IL and decomposition products coexist on the surface. Also, IRAS and XPS show indication of IL decomposition. Further heating leads to increased IL decomposition. The reaction products associated with the anions are volatile and leave the surface. In contrast, the cation fragments remain on the surface up to temperatures above 420 K.