Molekulární nanostruktury na površích
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- ItemSuperflux of an organic adlayer towards its local reactive immobilization(NATURE PORTFOLIO, 2023-10-18) Salamon, David; Bukvišová, Kristýna; Jan, Vít; Potoček, Michal; Čechal, JanOn-surface mass transport is the key process determining the kinetics and dynamics of on-surface reactions, including the formation of nanostructures, catalysis, or surface cleaning. Volatile organic compounds (VOC) localized on a majority of surfaces dramatically change their properties and act as reactants in many surface reactions. However, the fundamental question "How far and how fast can the molecules travel on the surface to react?" remains open. Here we show that isoprene, the natural VOC, can travel similar to 1 mu m s(-1), i.e., centimeters per day, quickly filling low-concentration areas if they become locally depleted. We show that VOC have high surface adhesion on ceramic surfaces and simultaneously high mobility providing a steady flow of resource material for focused electron beam synthesis, which is applicable also on rough or porous surfaces. Our work established the mass transport of reactants on solid surfaces and explored a route for nanofabrication using the natural VOC layer.
- ItemHow the Support Defines Properties of 2D Metal-Organic Frameworks: Fe-TCNQ on Graphene versus Au(111)(American Chemical Society, 2024-01-22) Jakub, Zdeněk; Trllová Shahsavar, Azin; Planer, Jakub; Hrůza, Dominik; Herich, Ondrej; Procházka, Pavel; Čechal, JanThe functionality of 2D metal-organic frameworks (MOFs) is crucially dependent on the local environment of the embedded metal atoms. These atomic-scale details are best ascertained on MOFs supported on well-defined surfaces, but the interaction with the support often changes the MOF properties. We elucidate the extent of this effect by comparing the Fe-TCNQ 2D MOF on two weakly interacting supports: graphene and Au(111). We show that the Fe-TCNQ on graphene is nonplanar with iron in quasi-tetrahedral sites, but on Au(111) it is planarized by stronger van der Waals interaction. The differences in physical and electronic structures result in distinct properties of the supported 2D MOFs. The d (2 )(z )center position is shifted by 1.4 eV between Fe sites on the two supports, and dramatic differences in chemical reactivity are experimentally identified using a TCNQ probe molecule. These results outline the limitations of common on-surface approaches using metal supports and show that the intrinsic MOF properties can be partially retained on graphene.
- ItemRapid oxygen exchange between hematite and water vapor(Nature Portfolio, 2021-11-10) Jakub, Zdeněk; Meier, Matthias; Kraushofer, Florian; Balajka, Jan; Pavelec, Jiří; Schmid, Michael; Franchini, Cesare; Diebold, Ulrike; Parkinson, Gareth S.Oxygen exchange at oxide/liquid and oxide/gas interfaces is important in technology and environmental studies, as it is closely linked to both catalytic activity and material degradation. The atomic-scale details are mostly unknown, however, and are often ascribed to poorly defined defects in the crystal lattice. Here we show that even thermodynamically stable, well-ordered surfaces can be surprisingly reactive. Specifically, we show that all the 3-fold coordinated lattice oxygen atoms on a defect-free single-crystalline "r-cut" (1 (1) over bar 02) surface of hematite (alpha-Fe2O3) are exchanged with oxygen from surrounding water vapor within minutes at temperatures below 70 degrees C, while the atomic-scale surface structure is unperturbed by the process. A similar behavior is observed after liquid-water exposure, but the experimental data clearly show most of the exchange happens during desorption of the final monolayer, not during immersion. Density functional theory computations show that the exchange can happen during on-surface diffusion, where the cost of the lattice oxygen extraction is compensated by the stability of an HO-HOH-OH complex. Such insights into lattice oxygen stability are highly relevant for many research fields ranging from catalysis and hydrogen production to geochemistry and paleoclimatology.
- ItemCO-Induced Dimer Decay Responsible for Gem-Dicarbonyl Formation on a Model Single-Atom Catalyst(WILEY-V C H VERLAG GMBH, 2024-04-15) Wang, Chunlei; Sombut, Panukorn; Puntscher, Lena; Jakub, Zdeněk; Meier, Matthias; Pavelec, Jiří; Bliem, Roland; Schmid, Michael; Diebold, Ulrike; Franchini, Cesare; Parkinson, Gareth S.The ability to coordinate multiple reactants at the same active site is important for the wide-spread applicability of single-atom catalysis. Model catalysts are ideal to investigate the link between active site geometry and reactant binding, because the structure of single-crystal surfaces can be precisely determined, the adsorbates imaged by scanning tunneling microscopy (STM), and direct comparisons made to density functional theory. In this study, we follow the evolution of Rh1 adatoms and minority Rh2 dimers on Fe3O4(001) during exposure to CO using time-lapse STM at room temperature. CO adsorption at Rh1 sites results exclusively in stable Rh1CO monocarbonyls, because the Rh atom adapts its coordination to create a stable pseudo-square planar environment. Rh1(CO)2 gem-dicarbonyl species are also observed, but these form exclusively through the breakup of Rh2 dimers via an unstable Rh2(CO)3 intermediate. Overall, our results illustrate how minority species invisible to area-averaging spectra can play an important role in catalytic systems, and show that the decomposition of dimers or small clusters can be an avenue to produce reactive, metastable configurations in single-atom catalysis. Time-lapse scanning tunneling microscopy movies are combined with theoretical computations to study CO adsorption on a model Rh1/Fe3O4(001) catalyst under ultrahigh vacuum conditions. Direct CO adsorption at Rh1 sites results in monocarbonyl species. Rh1-(CO)2 gem dicarbonyl species are observed, but from only via the CO-induced break-up of Rh2 dimer species.+ image
- ItemOxygen-Terminated (1x1) Reconstruction of Reduced Magnetite Fe3O4(111)(American Chemical Society, 2023-04-06) Kraushofer, Florian; Meier, Matthias; Jakub, Zdeněk; Hutner, Johanna; Balajka, Jan; Hulva, Jan; Schmid, Michael; Franchini, Cesare; Diebold, Ulrike; Parkinson, Gareth S.The (111) facet of magnetite (Fe3O4) has been studied extensively by experimental and theoretical methods, but controversy remains regarding the structure of its low-energy surface terminations. Using density functional theory (DFT) computations, we demonstrate three reconstructions that are more favorable than the accepted Feoct2 termination under reducing conditions. All three structures change the coordination of iron in the kagome Feoct1 layer to be tetrahedral. With atomically resolved microscopy techniques, we show that the termination that coexists with the Fetet1 termination consists of tetrahedral iron capped by 3-fold coordinated oxygen atoms. This structure explains the inert nature of the reduced patches.