20 November 2017

Exploring Molecular Functionalities on Surfaces

Title: Exploring Molecular Functionalities on Surfaces.
When: Friday, November 24, (2017), 12:00.
Place: Department of Condensed Matter Physics, Faculty of Science, Module 3, Seminar Room (5th Floor).
Speaker: Pavel Jelínek, Institute of Physics of the Czech Academy of Science, Prague, Czech Republic.

Implementation of fully functional devices based on the concept of Molecular electronics depends strongly on our ability to characterize, control and exploit properties of single molecules. Scanning probe technique offers the unique possibility to tackle these goals. As a proof, we will demonstrate control of electromechanical response and single electron charge manipulation within single molecules.

First, we will also discuss the piezoelectric effect in single helicene molecules on the Ag(111) surface, using the non-contact atomic force microscopy (AFM). The helicnes on the substrate forms circular and linear islands, which can be effectively disassembled to individual molecules by the AFM tip, to exclude collective influence on the piezoelectric measurements. Force spectroscopies reveal strong bias-induced deformations of the molecules as shown on Figure. The presence of the electric dipole coupled with a soft vibrational mode steaming from a helical structure of the molecule originates the strong piezoelectric effect. We corroborate the experimental evidence by the total energy DFT simulations.

Exploring Molecular Functionalities on Surfaces

Figure: (a) Ball-and-stick model of the experiment. (b) Measured Δf(z,VB) for the single molecule 7HdiET with the same tip: the frequency shift Δf vs. z-distance spectroscopies acquired for different bias voltages VB.

Second, we present experimental evidence of controlling multiple charge states on a single 2,6-Bis-ferrocenyl-naphthalene (bis-Fc) molecule, deposited on thin insulating NaCl film, by means of nc-AFM. The bis-Fc molecule consists of two ferrocene units, which allows stable formation of single and double charge states within a single bis-Fc molecule including their reversible transitions. The single electron charge state shows bi-stable configuration being localized on one of the ferrocene units. Moreover, we can modify the localization of the single electron charge state between two Fc units by lateral position of AFM probe. Thus, it represents prototypical model of the 2-level quantum system. We also detect strong electromechanical coupling between the charge state and SPM probe, showing possibility to design nanoelectromechanical systems on single molecular scale.

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