Michael Zharnikov

Universität Heidelberg, Heidelburg, Baden-Württemberg, Germany

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Publications (254)1121.77 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Understanding of the electric transport through surface-anchored metal-organic frameworks (SURMOFs) is important both from a fundamental perspective as well as with regards to possible future applications in electronic devices. To address this, mostly unexplored subject, we integrated a series of representative SURMOF thin films, formed by copper nodes and trimesic acid and known as HKUST-1, in a mercury-drop-based tunneling junction. While the transport properties of these SURMOFs are analogous to those of hybrid metal-organic molecular wires, manifested by a very low value of the tunneling decay constant (ß ≈ 0.006 Å-1), they are at the same time found to be consistent with a linear increase of resistance with film thickness. Upon loading of SURMOF pores with ferrocene (Fc), a noticeable increase in transport current was observed. A transport model and ab-initio electronic structure calculations were used to reveal a hopping transport mechanism and to relate the changes upon Fc loading to those of the electronic and vibrational structures of the SURMOF films.
    ACS Applied Materials & Interfaces 04/2015; DOI:10.1021/acsami.5b01792 · 5.90 Impact Factor
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    ABSTRACT: Selenolate is considered as an alternative to thiolate to serve as a headgroup mediating the formation of self-assembled monolayers (SAMs) on coinage metal substrates. There are however ongoing vivid discussions regarding the advantages and disadvantages of these anchor groups, regarding, in particular, the energetics of the headgroup-substrate interface and their efficiency in terms of charge transport/transfer. Here we introduce a well-defined model system of 6-cyanonaphthalene-2-thiolate and -selenolate SAMs on Au(111) to resolve these controversies. The exact structural arrangements in both types of SAMs are somewhat different, suggesting a better SAM building ability in the case of selenolates. At the same time, both types of SAMs have similar packing densities and molecular orientations. This permitted reliable competitive exchange and ion beam induced desorption experiments which provided an unequivocal evidence for a stronger bonding of selenolates to the substrate as compared to the thiolates. Regardless of this difference, the dynamic charge transfer properties of the thiolate and selenolate based adsorbates were found to be identical as determined by the core-hole-clock approach, which is explained by a redistribution of electron density along the molecular framework, compensating the difference in the substrate-headgroup bond strength.
    ACS Nano 04/2015; 9(4):4508–4526. DOI:10.1021/acsnano.5b01109 · 12.03 Impact Factor
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    ABSTRACT: Surface-confined hetero-metallic molecular triads (SURHMTs) were fabricated on SiO×-based solid substrates using optically-rich and redox-active Fe, Os, and Ru based terpyridyl complexes as metallo-ligands and Cu2+ ions as linkers. Optical and electrochemical studies reveal efficient electronic intra-molecular communication in these assemblies. The UV-vis spectra of the triads exhibit a superposition of the metal-to-ligand charge-transfer bands of individual complexes, providing a significant enlargement of the optical window, useful for application. Similarly, cyclic voltammograms of SURHMT layers show a variety of redox peaks corresponding to individual complexes as well as multi-redox states at a low potential. Interaction of a representative SURHMT assembly with redox active NOBF4 was investigated and used as a basis for configuring molecular logic gates.
    ACS Applied Materials & Interfaces 04/2015; DOI:10.1021/acsami.5b00953 · 5.90 Impact Factor
  • N. Meyerbroeker, P. Waske, M. Zharnikov
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    ABSTRACT: Self-assembled monolayers (SAMs) with amino tail groups are of interest due to their ability of coupling further compounds. Such groups can be, in particular, created by electron irradiation of nitro- or nitrile-substituted aromatic SAMs, which provide a basis for chemical nanolithography and the fabrication of functionalized nanomembranes. An estimate of reactivity of the created amino groups requires a reference system of homogeneous, amino-terminated aromatic SAMs, which can also be used as a highly reactive molecular template. Here, we describe the synthesis of 4′-aminobiphenyl-4-thiol (ABPT) and SAMs prepared from this precursor on Au(111). The monolayers were characterized by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy, which revealed that they are well defined, chemically uniform, densely packed, and highly ordered. To examine the influence of electron irradiation on the reactivity of the terminal amino groups, ABPT SAMs were exposed to low energy (50 eV) electrons up to a dose of 40 mC/cm2 and, subsequently, immersed in either trifluoroacetic, pentafluoropropionic, or heptafluorobutyric anhydride. Analysing the amount of the attached anhydride species made it possible to determine the percentage of reactive amino groups as well as the effect of steric hindrance upon the coupling reaction. The above results are compared with those obtained for the well-established nitro-substituted biphenylthiol monolayers.
    The Journal of Chemical Physics 03/2015; 142(10):101919. DOI:10.1063/1.4907942 · 3.12 Impact Factor
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    ABSTRACT: Here, we describe a universal photolithography setup for the patterning of biorepulsive self-assembled monolayers (SAMs) as well as other monomolecular films. The setup is based on commercial equipment consisting of a computer-controlled digital micromirror device chip combined with a suitable optics and a powerful light-emitting diode (LED) source delivering ultraviolet (UV) light with a wavelength of 375 nm. Digital patterns generated in the computer serve as an input for the chip, which modulates the reflected light accordingly, transferring the pattern to the sample surface. The performance of the setup was demonstrated by UV-induced modification of the nonsubstituted alkanethiolate (NS-AT) SAMs and biorepulsive oligo(ethylene glycol)-substituted AT (OEG-AT) monolayers on Au(111), upon homogeneous illumination of the test samples. Further, both nonspecific and specific templates for the protein adsorption were fabricated in the protein-repelling OEG-AT matrix by either direct writing or using an additional irradiation-promoted exchange reaction with a biotin-terminated AT. These templates were used either for nonspecific adsorption of bovine serum albumin (BSA) or for the specific adsorption of avidin, the latter relying on the interaction with the embedded biotin receptors. The density of the adsorbed protein layers across the patterns could be precisely varied by selection of proper irradiation doses.
    The Journal of Physical Chemistry C 12/2014; 119(1). DOI:10.1021/jp510809a · 4.84 Impact Factor
  • Journal of Physical Chemistry Letters 11/2014; 5:4143-4148. DOI:10.1021/jz502186a · 6.69 Impact Factor
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    ABSTRACT: The electronic structure of the amino acid L-cysteine in aqueous environment was studied using resonant inelastic soft x-ray scattering (RIXS) in a 2D map representation and analyzed in the framework of a "building block" approach. The element-selectivity of RIXS allows a local investigation of the electronic structure of the three functional groups of cysteine, namely the carboxyl, amino, and thiol groups, by measuring at the O K, N K, and S L2,3 edges, respectively. Variation of the pH value allows an investigation of molecules with protonated and deprotonated functional groups, which can then be compared with simple reference molecules that represent the isolated functional groups. We find that such "building blocks" can provide an excellent description of x-ray emission spectroscopy (XES) and RIXS spectra, but only if all nearest-neighbor atoms are included. This finding is analogous to the building-block principle commonly used in x-ray absorption spectroscopy. The building blocks show a distinct spectral character (fingerprint) and allow a comprehensive interpretation of the cysteine spectra. This simple approach opens the path to investigate the electronic structure of more complex biological molecules in aqueous solutions using XES and RIXS.
    The Journal of Physical Chemistry B 10/2014; DOI:10.1021/jp5089417 · 3.38 Impact Factor
  • Nikolaus Meyerbröker, Michael Zharnikov
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    ABSTRACT: Patterns of nanoparticles (NPs) on solid supports are usually restricted to a particular substrate or a class of substrates. Here we present a procedure which decouples the patterning step from the target substrate, enabling the fabrication of custom designed NP assemblies on nearly any solid support, including non-flat ones. The procedure relies on a hydrogel template prepared on the primary, conductive substrate and transferred to the target support as a sacrificial nanomembrane. The template is structured by electron beam lithography (EBL) which seals predefined areas of poly(ethylene glycol) based hydrogel film, making them inert to NP deposition in contrast to pristine areas that adsorb NPs in high densities. The deposition of NPs, occurring from an aqueous solution into the transferred membrane, follows EBL generated structure, delivering the desired NP pattern on the target support after removal of the organic matrix. Efficiency and flexibility of the procedure is illustrated by creating a variety of representative submicrometer patterns of densely packed gold and silver NPs on glass, including a useful pattern of a miniaturized quick-response code. The arrangement of NPs in these patterns corresponds to the negative image of EBL generated template. This significantly reduces the exposure time for designs where large areas covered with NPs are separated by thin, NP-free stripes.
    ACS Applied Materials & Interfaces 07/2014; 6(16). DOI:10.1021/am504358a · 5.90 Impact Factor
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    ABSTRACT: Heteroleptic copper(II)–polypyridyl complexes with extended p-conjugated, aromatic terminal units were immobilized on glass/Si substrates to intercalate DNA and cleave it upon photoexposure. Photonuclease activity is shown to be high, well reproducible and non-destructible towards the assembled complexes.
    Chemical Communications 07/2014; 50(78). DOI:10.1039/c4cc05063k · 6.72 Impact Factor
  • Frederick Chesneau, Michael Zharnikov
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    ABSTRACT: Using self-assembled monolayers (SAMs) of [1,1′;4′,1″-terphenyl]-4,4″-dimethanethiol (TPDMT) on Au as a test system and nickel as a test adsorbate, we demonstrate that the penetration of deposited metal atoms into a SAM can be completely inhibited by the preliminary formation of palladium-chloride seeding layer at the SAM–ambience interface. This layer is formed by a simple dipping procedure that takes only a few minutes. The palladium atoms in the seeding layer serve as nucleation centers for the growing metal film, staying at its bottom during the growth. In contrast, the chlorine atoms are transferred from palladium to the deposited metal, staying on the top of the growing metal film and serving as surfactants. The above approach is a perspective way to solve the well-known top contact problem at the formation of metal–SAM–metal assemblies that are of potential importance for future electronic and spintronic devices.
    The Journal of Physical Chemistry C 06/2014; 118(24):12980–12988. DOI:10.1021/jp505034h · 4.84 Impact Factor
  • Frederick Chesneau, Andreas Terfort, Michael Zharnikov
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    ABSTRACT: We studied the deposition of metal atoms (Ni as a test adsorbate) on fluorinated self-assembled monolayers (SAMs) using films of perfluoroterphenyl-substituted alkanethiols, C6F5(C6F4)2(CH2)3SH (FTP3), and partly fluorinated alkanethiols, F(CF2)10(CH2)2SH (F10H2), on Au(111) as representative test systems. Unlike the F10H2 films, their FTP3 counterparts were found to stop efficiently the penetration of nickel atoms into the SAM. The primary process is the Ni-mediated loss of fluorine atoms followed by extensive cross-linking between the partly defluorinated FTP backbones. The stability of these backbones and the rapid development of the intermolecular cross-linking, affecting predominantly the topmost part of the FTP3 SAM, are the key components to hinder the metal penetration. The chemically induced cross-linking in combination with the entirely reactive SAM represents a new concept to prepare a well-defined metal film at the SAM–ambience interface. This can be useful in context of novel metal/SAM-insulator/metal assemblies that are of potential interest for electronic and spintronic applications.
    The Journal of Physical Chemistry C 05/2014; 118(22):11763–11773. DOI:10.1021/jp5025334 · 4.84 Impact Factor
  • Nikolaus Meyerbröker, Michael Zharnikov
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    ABSTRACT: Extremely elastic and highly stable nanomembranes of variable thickness (5-350 nm) made completely of poly(ethylene glycol) are prepared by a simple procedure. The membranes exhibit distinct biorepulsive and hydrogel properties. They offer new possibilities for applications such as supports in transmission electron microscopy, matrices for inorganic nanoparticles, and pressure-sensitive elements for sensors.
    Advanced Materials 05/2014; 26(20). DOI:10.1002/adma.201305480 · 15.41 Impact Factor
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    ABSTRACT: Heterometallic, coordination-based, binary oligomer films were fabricated on SiOx-based solid substrates using successive layer-by-layer assembly of optically rich and redox-active polypyridyl complexes, Ru(pytpy)2·2PF6 (Ru-PT) and Os(pytpy)2·2PF6 (Os-PT) (where pytpy = 4′-pyridyl-2,2′:6′,2″-terpyridyl). The individual oligomer chains comprised alternating Ru-PT and Os-PT units connected via Cu2+, Pd2+, Ag+, Fe2+, Co2+, or Zn2+ metallo-linkers. The growth and properties of the oligomer films were monitored in detail by UV–vis spectroscopy and cyclic voltammetry. The films exhibited a linear growth upon addition of the successive building blocks, with a joint grafting density of 3.9–5.0 × 1014 metallo-ligands/cm2 for the final oligomer films (10 layers), corresponding to a characteristic area of 2.0–2.5 nm2/oligomer. The only exception was the Pd2+-linked film on glass that showed an exponential growth, which, however, could also be changed to the linear mode by the introduction of a conductive substrate. The combination of two different functional molecular units in the oligomer chains resulted in enhancement of the optical window and in an increase in the number of the available redox states as compared to the analogous single component assemblies.
    The Journal of Physical Chemistry C 04/2014; 118(18):9578–9587. DOI:10.1021/jp502166k · 4.84 Impact Factor
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    ABSTRACT: While it is well-known that oligoethylene glycol (OEG) terminated self-assembled monolayers (SAMs) can be deteriorated by UV irradiation in air, we now report that the analogous modification can also be performed in water, opening the opportunity for in situ tuning of biorepulsive properties. Surprisingly, this deterioration also takes place even in the absence of molecular oxygen, resulting in a very selective process.
    Chemical Communications 03/2014; DOI:10.1039/c4cc00982g · 6.72 Impact Factor
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    ABSTRACT: Nanoscopic metal-molecule-metal junctions consisting of Fe-bis(terpyridine)-based ordered nanostructures grown in layer-by-layer fashion on a solid support are investigated by conductive atomic force microscopy, as described on page 1688 by P. Samorì, A. Licciardello, A. Troisi and co-workers. Hopping is demonstrated as the main charge-transport mechanism both experimentally and theoretically.
    Advanced Materials 03/2014; 26(11):1792. DOI:10.1002/adma.201470074 · 15.41 Impact Factor
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    ABSTRACT: Nanoscopic metal–molecule–metal junctions consisting of Fe‐bis(terpyridine)‐based ordered nanostructures are grown in layer‐by‐layer fashion on a solid support. Hopping is demonstrated as the main charge‐transport mechanism both experimentally and theoretically.
    Advanced Materials 03/2014; 26(11). DOI:10.1002/adma.201304848 · 15.41 Impact Factor
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    M. Nuruzzaman Khan, Michael Zharnikov
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    M. Nuruzzaman Khan, Michael Zharnikov
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    M. Nuruzzaman Khan, Michael Zharnikov
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Publication Stats

6k Citations
1,121.77 Total Impact Points

Institutions

  • 1998–2015
    • Universität Heidelberg
      • Institute of Physical Chemistry
      Heidelburg, Baden-Württemberg, Germany
  • 2007
    • Philipps University of Marburg
      Marburg, Hesse, Germany
    • Universität Regensburg
      • Institute of Analytical Chemistry, Chemo and Biosensors
      Ratisbon, Bavaria, Germany
    • Washington University in St. Louis
      • Department of Chemistry
      San Luis, Missouri, United States
  • 2004–2007
    • National Cheng Kung University
      • Department of Materials Science and Engineering
      臺南市, Taiwan, Taiwan
    • University of Hamburg
      Hamburg, Hamburg, Germany
    • University of Nevada, Las Vegas
      • Department of Chemistry
      Las Vegas, Nevada, United States
  • 2006
    • National Synchrotron Radiation Research Center (NSRRC)
      Hsin-chu-hsien, Taiwan, Taiwan
    • Pennsylvania State University
      • Department of Chemistry
      University Park, MD, United States
  • 2005
    • Bar Ilan University
      • Department of Chemistry
      Gan, Tel Aviv, Israel
  • 2003–2004
    • Karlstads universitet
      Karlstad, Värmland, Sweden
  • 2002
    • Chung Yuan Christian University
      • Department of Biomedical Engineering
      Hsinchu, Taiwan, Taiwan
  • 1995–1998
    • Max Planck Institute of Microstructure Physics
      • Experimental Department 2
      Halle-on-the-Saale, Saxony-Anhalt, Germany
    • Technische Universität München
      München, Bavaria, Germany