Working Group Quantum Control

Current research interests:

 

Tripodal Molecular Platforms

We address functional tripodal molecules on surfaces as to control and monitor their state. We therefore developed various novel experimental methodologies, which allow the controllable positioning, characterization, addressing and switching of single molecular functional units.

One example is an electrically actuated molecular toggle switch where we used a spirobifluorene variant with a well-defined spatial arrangement of the nitrile head group. This allows to exert forces on the molecule by application of electric fields (s. Fig.1)[1]. We intend to extend this research towards the realisation of electrically driven Molecular Motors.

Another example is a Molecular Graph Paper: Using the tip of an STM, the acetyl group that sticks out of a molecular film can be removed in a controlled way. The chemically modified molecule can readily be distinguished from the original ones so that writing and reading information on the nanoscale becomes possible (s. Fig.2)[2].

 

Fig.1:   Top: Toggle switch mechanism due to the dipole moment p and the electric field ε as indicated in the molecular models.
Bottom: Time traces of applied voltage and resulting current during bistable switching between the two states [1].
Fig.2  Top: Chemical modification of the molecule on applying a voltage pulse from the STM tip.
Bottom: Writing experiment at 5.3K [2].

Selected Publications:
(1)   L. Gerhard et al., Nat. Commun. 8 (2017) 14672
(2)   M. Lindner et al., Angew. Chem. Int. Ed. 56 (2017) 8290

 

Light emission from the STM junction

Scanning Tunneling Microscopy allows to investigate the light emission from atomic scale materials regions as defined by the tunnel contact area.

We use this tool for basic research on the electroluminescence of single molecules to investigate the connection of the local electronic structure with the light emission (s. Fig.3).

Furthermore, we developed a low temperatur STM which allows a stable measurement of samples at 1.5 K. The long holding time of several days allows extensive experiments without interruption which are necessary especially for combined measurements of electronic and optical properties on individual molecules with submolecular precision.

 

Fig.3: Schematics of the spectroscopic investigation of light emission of molecules under STM observation.
Fig.4: STM-light measuring head of the Low temperature STM and recorded spectroscopic data.

Selected Publications:
(3)   K. Edelmann et al., Rev. Sci. Instrum. 89 (2018) 123107
(4)   K. Edelmann et al., Phys. Rev. B 101 (2020) 205405