Tuning magnetic properties in molecular magnetic systems
Final Report Abstract
The detailed knowledge of the static and dynamic properties of single organic molecules in contact to electrodes is of fundamental interest for the development of any single molecular device. Within this project several key experiments have been performed, deepening the understanding and control of electronic, optical and magnetic properties of functional molecular units on surfaces. In these studies, the substrate on which the units are anchored provides an additional degree of freedom to tailor their physical behavior. We exploit the large variety of possibilities offered by low temperature scanning tunneling microscopy (STM) to access these properties in real space on the atomic scale and to obtain insights into their dynamics. Atomically precise control of single functional molecular units: Molecular switches are functional compounds that can be reversibly and repeatedly interconverted between stable states. We demonstrated that the surface electronic state present on a Cu(111) surface allows a reversible parallel addressing, and hence “remotely controlled” switching, of an entire ensemble of single molecules within distances on the order of 100nm. Precise activation of a chemical reaction is demonstrated on the example of a direct desulfurization process of a single thiphen unit. Imaging of the individual atomic positions within the organic molecule allows unambiguous determination of the two involved broken C-S bonds. Combining two powerful techniques, the electrospray ion beam deposition and a low temperature STM, using an ultra-high vacuum transfer system, opens new perspectives for high resolution spectroscopic imaging of biologically relevant systems on surfaces, such as peptides. We are just beginning to explore this “terra incognita” and presented first examples into the direction of peptide sequencing on surfaces. Optical properties: The fast exchange of information plays an important role in the development of present day devices. The manipulation of light at the nanoscale, far below the diffraction limit, is indeed possible by coupling it to plasmons, collective charge fluctuations in metals. We contributed surprising results on single iridium complexes deposited on organic buffer layers demonstrating two new basic working principles of plasmonic light emitting devices. In our study we exploit the intrinsic properties of the iridium complex on a C60 buffer layer, featuring specific and well defined states to tailor plasmon excitation on the single molecular level. The first study shows that molecular orbitals can serve as energetically and spatially defined nanogates for plasmon emission. Thus light having wavelengths of several hundred nanometers can be locally controlled via a single molecular orbital. This experiment was considered a breakthrough by the editor of Nature Photonics (highlighted in: research highlight Nature Plasmonics 7). In the second device we could realize a plasmon-generating single-molecule field-effect transistor, which operates on the level of a single electronic charge and at least in the GHz range. This finding is even more important since it presents a missing link to combine electronics with plasmonics. Magnetic properties: On surfaces, the electronic properties of magnetic complexes can be either tailored by the bare metal surface itself or by adsorption on specific templates. Here we could show that single metal centers in metal organic networks serve as attractive adsorption sites for the self-assembled growth of subsequent deposited metal atoms. These additional deposited atoms strongly alter the magnetic properties of the metal coordination centers and in the studied case lead to a recovery of the magnetic moment that originally had been quenched on the bare surface. Another interesting class of molecular spin systems are pure organic radicals. For the first time we could access locally the behavior of such spin systems and study the coupling between conduction electrons of a metal surface and a spin ½ system centered on the organic radical group in the weak coupling limit of the Kondo effect.
Publications
- Formation of Fe Cluster Superlattice in a Metal-Organic Quantum-Box Network, Physical Review Letters 110, 086102 (2013)
M. Pivetta, G.E. Pacchioni, U. Schlickum, J.V. Barth, and H. Brune
(See online at https://doi.org/10.1103/PhysRevLett.110.086102) - Molecular Orbital Gates for Plasmon Excitation, Nano Letters 13, 2846 (2013)
T. Lutz, C. Große, C. Dette, A. Kabakchiev, F. Schramm, M. Ruben, R. Gutzler, K. Kuhnke, U. Schlickum, and K. Kern
(See online at https://doi.org/10.1021/nl401177b) - Temperature and magnetic field dependence of a Kondo system in the weak coupling regime, Nature Communication 4, 2110 (2013)
Y.H. Zhang, S. Kahle, T. Herden, C. Stroh, M. Mayor, U. Schlickum, M. Ternes, P. Wahl, and K. Kern
(See online at https://doi.org/10.1038/ncomms3110) - Dynamic Control of Plasmon Generation by an Individual Quantum System, Nano Letters 14, 5693 (2014)
C. Große, A. Kabakchiev, T. Lutz, R. Froidevaux, F. Schramm, M. Ruben, M. Etzkorn, U. Schlickum, K. Kuhnke, and K. Kern
(See online at https://doi.org/10.1021/nl502413k) - Bipolar conductance switching of single anthraditiophene molecules, ACS Nano 9, 12506 (2015)
B. Borca, V. Schendel, R. Pétuya, I. Pentegov, T. Michnowicz, U. Kraft, H. Klauk, A. Arnau, P. Wahl, U. Schlickum, and K. Kern
(See online at https://doi.org/10.1021/acsnano.5b06000) - Restoring the Co Magnetic Moments at Interfacial Co-Porphyrin Arrays by Site-Selective Uptake of Iron, ACS Nano 9, 3605 (2015)
S. Vijayaraghavan, W. Auwärter, D. Écija, K. Seufert, S. Rusponi, T. Houwaart, P. Sautet, M. L. Bocquet, P. Thakur, S. Stepanow, U. Schlickum, M. Etzkorn, H. Brune, and J.V. Barth
(See online at https://doi.org/10.1021/nn507346x) - Remotely controlled isomer selective molecular switching, Nano Letters 16, 93 (2016)
V. Schendel, B. Borca, I. Pentegov, T. Michnowicz, U. Kraft, H. Klauk, P. Wahl, U. Schlickum, and K. Kern
(See online at https://doi.org/10.1021/acs.nanolett.5b02974) - Electric field driven direct desulfurization, ACS Nano 11, 4703 (2017)
B. Borca, T. Michnowicz, R. Pétuya, M. Pristl, V. Schendel, I. Pentegov, U. Kraft, H. Klauk, P. Wahl, R. Gutzler, A. Arnau, U. Schlickum, and K. Kern
(See online at https://doi.org/10.1021/acsnano.7b00612) - Pentacene adsorption and electronic properties on thin decoupling layers, Beilstein Journal of Nanotechnology 8, 1388 (2017)
S. Koslowski, D. Rosenblatt, A. Kabakchiev, K. Kunhke, K. Kern, and U. Schlickum
(See online at https://doi.org/10.3762/bjnano.8.140) - Strong paramagnon scattering in single atom Pd contacts. Phys. Rev. B 86, 035155 (2017)
V. Schendel, C. Barreteau, M. Brandbyge, B. Borca, I. Pentegov, U. Schlickum, M. Ternes, P. Wahl, and K. Kern
(See online at https://doi.org/10.1103/PhysRevB.96.035155)
