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TT: Fachverband Tiefe Temperaturen

TT 25: Nonequilibrium Quantum Systems I (joint session TT/DY)

TT 25.13: Vortrag

Dienstag, 19. März 2024, 12:45–13:00, H 3005

Tuning the switching behavior of oligophenyls in metal-molecule-metal junctions by fluorine substituents — •Shengming Zhang¹, Zhiqiang Li², Joachim Reichert¹, Hai Bi², and Johannes Barth¹ — ¹Physics Department E20, Technical University of Munich, Germany — ²Jihua Laboratory, Foshan, China

Single-molecule junctions represent a promising avenue in the realm of nanometer-scale electronic device development. Numerous investigations have concentrated on the I-V relationship, which often falls short in fully characterizing a single-molecule junction. In our study, we use Raman spectroscopy as a complementary tool to explore the vibrational states of individual, covalently bound molecules while sweeping the bias. Our focus is on a series of three terphenyl species. The first molecule incorporates four methyl side groups which aim to hinder the planarization of the neutral molecules. The molecules get transiently charged above a certain threshold voltage and coplanarize their phenyl rings. This conformational change goes along with an extension of the π-electron system, increases the polarizability and thus the Raman activity of the molecules significantly. In the second and third molecule, one resp. two methyl groups where fluorine substituted in order to tune the alignment of the HOMO to the Fermi level of the electrodes upon junction formation. This way, we can steer the threshold voltage where transient charging is planarizing the molecule. This approach underscores the tunability of characteristic transport properties in a molecular model system by intricate changes in its molecular structure.

Keywords: single-molecule junction; Raman spectroscopy; molecular switch