Molekulární nanostruktury na površích

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    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
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    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.
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    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.
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    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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    Superflux of an organic adlayer towards its local reactive immobilization
    (NATURE PORTFOLIO, 2023-10-18) Salamon, David; Bukvišová, Kristýna; Jan, Vít; Potoček, Michal; Čechal, Jan
    On-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.