Molekulární nanostruktury na površích

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Rapid 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.
Counting statistics of single electron transport in bilayer graphene quantum dots
(American Physical Society, 2023-01-24) Garreis, Rebekka; Gerber, Jonas Daniel; Stará, Veronika; Tong, Chuyao; Gold, Carolin; Röösli, Marc; Watanabe, Kenji; Taniguchi, Takashi; Ensslin, Klaus; Ihn, Thomas; Kurzmann, Annika
We measured telegraph noise of current fluctuations in an electrostatically defined quantum dot in bilayer graphene by real-time detection of single electron tunneling with capacitively coupled neighboring quantum dot. Suppresion of the second and third cumulant (related to shot noise) in a tunable graphene quantum dot is demonstrated experimentally. With this method we demonstrate the ability to measure very low current and noise levels. Furthermore, we use this method to investigate the first spin excited state, an essential prerequisite to emasure spin relaxation
ProLEED Studio: software for modeling low-energy electron diffraction patterns
(INT UNION CRYSTALLOGRAPHY, 2024-02-01) Procházka, Pavel; Čechal, Jan
Low-energy electron diffraction patterns contain precise information about the structure of the surface studied. However, retrieving the real space lattice periodicity from complex diffraction patterns is challenging, especially when the modeled patterns originate from superlattices with large unit cells composed of several symmetry-equivalent domains without a simple relation to the substrate. This work presents ProLEED Studio software, built to provide simple, intuitive and precise modeling of low-energy electron diffraction patterns. The interactive graphical user interface allows real-time modeling of experimental diffraction patterns, change of depicted diffraction spot intensities, visualization of different diffraction domains, and manipulation of any lattice points or diffraction spots. The visualization of unit cells, lattice vectors, grids and scale bars as well as the possibility of exporting ready-to-publish models in bitmap and vector formats significantly simplifies the modeling process and publishing of results.
Polymer pencil leads as a porous nanocomposite graphite material for electrochemical applications: The impact of chemical and thermal treatments
(Elsevier, 2021-05-01) Trnková, Libuše; Třísková, Iveta; Čechal, Jan; Farka, Zdeněk
Pencil graphite electrodes are a simple, disposable, and low-cost alternative to screen-printed graphite electrodes. In terms of stability and sensitivity, pencil electrodes often outperform conventional carbon ones. This paper discusses and emphasizes the superior properties of polymer pencil graphite electrodes (pPeGEs), which can be exploited in the electrochemical analysis of molecules, such as chlorides, whose signals are missing on common graphite electrodes. The chemical and structural behaviour of pencil leads after exposure to acids (HF, HNO3, HClO4) or organic solvents (CH3CN, CH3Cl) was monitored via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The electrochemical activity of pristine and treated pPeGEs was studied by the cyclic voltammetry (CV) responses of reversible redox probes [Fe(CN)6]3/4- and [Ru(NH3)6]3+/ 2+. XPS proved the presence of siloxanes in the surface matrix of the pencil leads; this finding relates to the hydrophobic surface character of the electrodes. SEM then provided images of the pencil surfaces with microplates and flakes and revealed the removal of siloxanes upon chemical treatment. The CVs of non-dried and dried pPeGEs displayed surface changes in the polymer matrix, accompanied by water loss. Our study shows that the pPeGE retains the character of a stable graphite sensor when exposed to acids and organic solvents, except for HF and chloroform. The discovered effects explain the electrochemical processes occurring on pPeGEs and can contribute to their application in electrochemical sensing and energy storage.
Complex k-uniform tilings by a simple bitopic precursor self-assembled on Ag(001) surface
(Springer Nature, 2020-12-01) Kormoš, Lukáš; Procházka, Pavel; Makoveev, Anton Olegovich; Čechal, Jan
The realization of complex long-range ordered structures in a Euclidean plane presents a significant challenge en route to the utilization of their unique physical and chemical properties. Recent progress in on-surface supramolecular chemistry has enabled the engineering of regular and semi-regular tilings, expressing translation symmetric, quasicrystalline, and fractal geometries. However, the k-uniform tilings possessing several distinct vertices remain largely unexplored. Here, we show that these complex geometries can be prepared from a simple bitopic molecular precursor – 4,4’-biphenyl dicarboxylic acid (BDA) – by its controlled chemical transformation on the Ag(001) surface. The realization of 2- and 3-uniform tilings is enabled by partially carboxylated BDA mediating the seamless connection of two distinct binding motifs in a single long-range ordered molecular phase. These results define the basic self-assembly criteria, opening way to the utilization of complex supramolecular tilings.

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