Project title

Local control of single-molecule conductivity probed by scanning tunneling microscopy and spectroscopy

Principal investigators

Dr. Lucia Vitali, Dr. Peter Wahl and Prof. Dr. Klaus Kern, Max Planck Institute for Solid State Research, Stuttgart

Abstract

Our project aims to study by local probe spectroscopy at low temperatures the electronic transport through a single molecule bonded to a metallic substrate. We want to complement morphology and electronic structure of the molecules obtained by conventional scanning tunneling microscopy/spectroscopy by transport properties extracted from point contact spectroscopy. This combination not only offers a unique opportunity to deepen our understanding of the role of the electronic and vibrational excitations in molecular electronic transport, and to address the determining role of the molecule-metal contacts. Functional molecules with structural and/or electronic/magnetic bi-stability will be attached to copper single crystal surfaces via carboxylate bonding. The influence of the geometric and chemical structure on the molecule-metal contact will be studied in detail and we aim to control the transport through manipulation of the local contact environment. For the functional molecules incorporating magnetic centers we will also explore the possibility to modulate the transport with magnetic field via the Kondo screening.

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Local control of single-molecule conductivity probed by scanning tunneling microscopy and spectroscopy

the correlation between morphology, electronic and vibrational structure of the molecules in the transport properties. This can be achieved by complementing topographic elastic and inelastic spectroscopy by point contact spectroscopy. Particular attention will be given to the molecular adsorption orientation. We will consider different molecular ending groups in order to assure the upright standing orientation of the molecule on the metal surface and to optimize the molecule-metal contact resistance.

the role of impurities or of structural disorder in the proximity of the molecule as a build-in electrostatic potential. At this aim specific atomic species will be co-deposited or manipulated with the STM tip in order to control the impurity-molecule distance. Also the interaction of neighboring molecules can be addressed by increasing the deposited coverage. In a successive step the dominant contributions to the conductance deriving from the energy level alignment, formation of molecule-substrate contact potential and tip induced field effects will be understood by the comparison of the spectra obtained in tunneling and in point contact mode. Furthermore, the effect of a magnetic field on the transport through a molecular wire can be studied to investigate the spin-dependent transport properties of single molecules.

the role of inelastic channels in the electron transport. These will give insight in the structural configuration of the molecules. We aim to tune the structural configuration of the molecule by a mechanical interaction with the tip of the scanning tunneling microscope.