arXiv subjects

Katharina J. Franke

Publications and source records attributed to Katharina J. Franke.

57 records · Page 4Linked to original sources

arXiv2012

Gating the charge state of a single molecule by local electric fields

The electron acceptor molecule TCNQ is found in either of two distinct integer charge states when embedded into a monolayer of a charge transfer-complex on a gold surface. Scanning tun- neling spectroscopy measurements identify these states through the presence/absence of a zero-bias Kondo resonance. Increasing the (tip-induced) electric field allows us to reversibly induce the ox- idation/reduction of TCNQ species from their anionic or neutral ground state, respectively. We show that the different ground states arise from slight variations in the underlying surface potential, pictured here as the gate of a three-terminal device.

cond-mat.mes-hall↗

arXiv2012

Induction of a photostationary ring-opening/closing state of spiropyran monolayers on the semi-metallic Bi(110) surface

Molecular switches on metal surfaces typically show very little photoreactivity. Using scanning tunneling microscopy we show that the ring-opening/-closing switch nitrospiropyran thermally and optically isomerizes to the open merocyanine form on a Bi(110) surface. Irradiation by blue light of a monolayer spiropyran molecules leads to mixed domains of the two isomers. At large illumination intensities a photostationary state is established, indicating the bidirectional ring-opening and closing reaction of these molecules on the bismuth surface. The enhanced photoactivity contrasts with the case of adsorption on other metal surfaces, probably due to the low density of states at the Fermi level of the semi-metallic Bi(110) surface.

cond-mat.mtrl-sci↗

arXiv2008

Resonant heating and substrate-mediated cooling of a single C60 molecule in a tunnel junction

We study the influence of different metallic substrates on the electron induced heating and heat dissipation of single C60 molecules in the junction of a low temperature scanning tunneling microscope. The electron current passing through the molecule produces a large amount of heat due to electron-phonon coupling, eventually leading to thermal decomposition of the fullerene cage. The power for decomposition varies with electron energy and reflects the resonance structure participating in the transport. The average value for thermal decomposition of C60 on Cu(110) amounts to 21 $μ$W, while it is much lower on Pb(111) (2.9 $μ$W) and on Au(111) (1.0 $μ$W). We ascribe this difference to the amount of charge transfer into C60 upon adsorption on the different surfaces, which facilitates molecular vibron quenching by electron-hole pair creation.

cond-mat.mtrl-sci↗