Fermi surfaces of transition metals, which describe all thermodynamical and transport quantities of solids, often fail to be modeled by one-electron mean-field theory due to strong correlations among the valence electrons. In addition, relativistic spin-orbit coupling pronounced in heavier elements lifts the degeneracy of the energy bands and further modifies the Fermi surface. Palladium and rhodium, two 4d metals attributed to show significant spin-orbit coupling and electron correlations, are ideal for a systematic and fundamental study of the two fundamental physical phenomena and their interplay in the electronic structure. In this study, we explored the Fermi surface of the 4d noble metals palladium and rhodium obtained via high-resolution constant initial state momentum microscopy. The complete 3D-Fermi surfaces of palladium and rhodium were tomographically mapped using soft X-ray photon energies from 34 eV up to 660 eV. To fully capture the orbital angular momentum of states across the Fermi surface, the Fermi surface tomography was performed using p- and s- polarized light. Applicability and limitations of the nearly-free electron final state model in photoemission are discussed using a complex band structure model supported by experimental evidence. The significance of spin-orbit coupling and electron correlations across the Fermi surfaces will be discussed within the context of the photoemission results. State-of-the-art fully relativistic Korringa-Kohn-Rostoker (KKR) calculations within the one-step model of photoemission are used to support the experimental results.
- Klíčová slova
- Complex band structure, Fermi surface tomography, Final-state self-energy, Momentum microscopy, Photoelectron final-state,
- Publikační typ
- časopisecké články MeSH
By means of electrocatalytic tests, surface-science techniques and density functional theory, we unveil the physicochemical mechanisms ruling the electrocatalytic activity of recently discovered mitrofanovite (Pt3Te4) mineral. Mitrofanovite represents a very promising electrocatalyst candidate for energy-related applications, with a reduction of costs by 47% compared to pure Pt and superior robustness to CO poisoning. We show that Pt3Te4 is a weak topological metal with the Z2 invariant, exhibiting electrical conductivity (∼4 × 106 S/m) comparable with pure Pt. In hydrogen evolution reaction (HER), the electrode based on bulk Pt3Te4 shows a very small overpotential of 46 mV at 10 mA cm-2 and a Tafel slope of 36-49 mV dec-1 associated with the Volmer-Heyrovsky mechanism. The outstanding ambient stability of Pt3Te4 also provides durability of the electrode and long-term stability of its efficient catalytic performances.
- Publikační typ
- časopisecké články MeSH
We investigate the structural and electronic properties of nitrogen-doped epitaxial monolayer graphene and quasifreestanding monolayer graphene on 6H-SiC(0001) by the normal incidence x-ray standing wave technique and by angle-resolved photoelectron spectroscopy supported by density functional theory simulations. With the location of various nitrogen species uniquely identified, we observe that for the same doping procedure, the graphene support, consisting of substrate and interface, strongly influences the structural as well as the electronic properties of the resulting doped graphene layer. Compared to epitaxial graphene, quasifreestanding graphene is found to contain fewer nitrogen dopants. However, this lack of dopants is compensated by the proximity of nitrogen atoms at the interface that yield a similar number of charge carriers in graphene.
- Publikační typ
- časopisecké články MeSH
Chemical doping is one of the most suitable ways of tuning the electronic properties of graphene and a promising candidate for a band gap opening. In this work we report a reliable and tunable method for preparation of high-quality boron and nitrogen co-doped graphene on silicon carbide substrate. We combine experimental (dAFM, STM, XPS, NEXAFS) and theoretical (total energy DFT and simulated STM) studies to analyze the structural, chemical, and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of boron and nitrogen substitutional defects can be achieved in the STM channel due to the quantum interference effect, arising due to the specific electronic structure of nitrogen dopant sites. Chemical reactivity of single boron and nitrogen dopants is analyzed using force-distance spectroscopy by means of dAFM.
- Klíčová slova
- boron, chemical reactivity, doping, graphene, nitrogen,
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
