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Under near-ambient pressure conditions, carbon monoxide molecules intercalate underneath an epitaxial graphene monolayer grown on Ni(111), getting trapped into the confined region at the interface. On the basis of ab-initio density functional theory calculations, we provide here a full investigation of the intercalated CO pattern, highlighting the modifications induced on the graphene electronic structure. For a CO coverage as low as 0.14 monolayer (ML), the graphene layer is spatially decoupled from the metallic substrate, with a significant C 1s core level shift towards lower binding energies. The most relevant signature of the CO intercalation is a clear switching of the graphene doping state, which changes from n-type, when strongly interacting with the metal surface, to p-type. The shift of the Dirac cone linearly depends on the CO coverage, reaching about 0.9 eV for the saturation value of 0.57 ML. Theoretical predictions are compared with the results of scanning tunnelling microscopy, low-energy electron diffraction and photoemission spectroscopy experiments, which confirm the proposed scenario for the nearly saturated intercalated CO system. This result opens the way to the application of the graphene/Ni(111) interface as gas sensor to easily detect and quantify the presence of carbon monoxide.

We have studied zirconia films on a Rh(111) substrate with thicknesses in the range of 2–10 monolayers (ML) using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Zirconia was deposited using a UHV-compatible sputter source, resulting in layer-by-layer growth and good uniformity of the films. For thicknesses of 2–4 ML, a layer-dependent influence of the substrate on the structure of the thin films is observed. Above this thickness, films show a (2 × 1) or a distorted (2 × 2) surface structure with respect to cubic ZrO2(111); these structures correspond to tetragonal and monoclinic zirconia, respectively. The tetragonal phase occurs for annealing temperatures of up to 730 °C; transformation to the thermodynamically stable monoclinic phase occurs after annealing at 850 °C or above. High-temperature annealing also breaks up the films and exposes the Rh(111) substrate. We argue that the tetragonal films are stabilized by the interface to the substrate and possibly oxygen deficiency, while the monoclinic films are only weakly defective and show band bending at defects and grain boundaries. This observation is in agreement with positive charge being responsible for the grain-boundary blocking effect in zirconia-based solid electrolytes. Our work introduces the tetragonal and monoclinic 5 ML-thick ZrO2 films on Rh(111) as a well-suited model system for surface-science studies on ZrO2, as they do not exhibit the charging problems of thicker films or the bulk material and show better homogeneity and stability than the previously-studied ZrO2/Pt(111) system.

Recent years have witnessed great advances in graphene coatings for improving the conductivity and cycling performance of non-carbonaceous anode materials (e.g., metal oxides, Si and Ge) towards advanced lithium-ion batteries (LIBs). However, the ubiquitously-used, chemically-exfoliated graphene wrapping layers within LIBs still face daunting challenges in the limited electronic transport and uncontrolled solid electrolyte interphase growth, which lead to the degradation of reversible capacity and cycling stability. Herein, we demonstrate an ingenious chemical vapor deposition strategy to realize in-situ conformal growth of graphene on MnO nanorods mediated by methane carburization. Fundamentally different from the chemically-exfoliated counterparts, the thus-grown graphene layers exhibit highly tunable crystallinity and thickness to optimize charge transport for the hermetically-isolated MnO anode materials from electrolyte. In turn, the graphene shell-isolated MnO anode manifests the enhanced stability over long-term cycling and rate capability, as compared to the previous MnO-based counterparts. Our work would provide a novel insight into the state-of-the-art design of high-rate and long-life graphene/metal oxide-based electrodes targeting future-generation LIBs.