Regensburg 2019 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 12: HL Poster I

HL 12.41: Poster

Montag, 1. April 2019, 17:30–20:00, Poster E

New insight into electronic excitations of metal phthalocyanines — •Louis Philip Doctor, Marco Naumann, Lukas Graf, Nikolay Kovbasa, and Martin Knupfer — IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany

We deposited thin films with a thickness of 120 nm, of copper-, zinc- and nickel-phthalocyanine on a KBr substrate in ultra-high vacuum, respectively. Afterwards these thin films underwent a phase transition to the β-phase. Furthermore the optical absorption spectra were measured at different temperatures down to 77 K. They show a drastic difference in the absorption of the initially evaporated α-phase compared to the β-phase in all optical regimes. The four peaks in the visible regime can be each assigned to a dipole transition element, which can be modelled by the extended double dipole approach. This model calculates the interaction between the two molecules in a metal-phthalocyanine dimer from crystallographic data. We added a distortion angle to model a momentum dependent dipole interaction. With electron-energy-loss-spectroscopy we are able to measure a momentum dependent excitation. Here again we see a different behaviour of the excitons in the α- and β-phase. The first excitation peak underwent a redshift for higher momentum transfer, whereas the second excitation peak virtually vanishes at the same time. This behaviour can be seen until a momentum transfer of 0.7 Å⁻¹. For higher momentum transfer this process seems to revert to the initial spectrum. This leads to the conclusion that excitons in metal-phthalocyanines have a negative dispersion with a minimum around 0.7 Å⁻¹.