Scanning tunneling microscopy studies of light-induced switching of diarylethenes & functionalized graphene

PhD ceremony: Mr. A. Arramel, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Scanning tunneling microscopy studies of light-induced switching of diarylethenes & functionalized graphene

Promotor(s): prof. B.J. van Wees, prof. B.L. Feringa

Faculty: Mathematics and Natural Sciences

The thesis of Arramel investigates two interesting topics: molecular switching and functionalized graphene on a solid surface. In order to study these respective interests, scanning tunneling microscopy is introduced as a characterization tool of the nanostructure at the single molecule level.

Arramel’s primary projects involved the investigation of the molecular switching behavior on gold surface. In particular, this thesis is dedicated to demonstrate the light-induced photoswitching behavior of the new class of diarylethene switches embedded in the self-assembled monolayers of dodecanethiol matrices at room temperature. One of the molecules of interest is S,S'-((4,4'-(perfluorocyclopent-1-ene-1,2-diyl)bis(5-methylthiophene-4,2-diyl))bis(4,1-phenylene)) diethanethiolate (abbreviated as As-DE). In addition, the charge transport properties of the molecular switches were measured using Scanning Tunneling Spectroscopy (STS) at low temperature. The I-V characteristics show that the Highest Occupied Molecular Orbitals and the Lowest Unoccupied Molecular Orbitals were successfully determined.

In the second part of the thesis, an attempt to open the electronic band gap in graphene via two approaches: reversible hydrogenation and porphyrins physisorption is investigated, respectively. The former involves the reactive ion etching technique to hydrogenate the graphene surface The chemisorption of hydrogen atoms changes the sp2 hybridization of carbon atoms to tetragonal sp3 hybridization, consequently modifying the surface geometry and local electronic properties. Moreover, the reversible bandgap opening of the graphene is possible by means of the thermal annealing. Another approach to open a gap in graphene is using the adsorption of porphyrins to introduce the charge transfer effect onto the chemically vapor deposition (CVD) graphene surface.