Vibration Spectra of 2D FePc on Au (111) observed by STM-IETS at 77K

Pratyay Amrit^1*, Naoya Kawakami¹, Yen-Yu Lai¹, Emi Minamitani², Ryuichi Arafune³, Noriaki Takagi⁴, Chun-Liang Lin¹

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Institute for Molecular Science, Institute for Molecular Science, Okazaki, Japan
³International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Ibaraki, Japan
⁴Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan

* Presenter:Pratyay Amrit, email:pratyay.sc08@nycu.edu.tw

The vibrational property of molecules is strongly correlated to the adsorption sites and adsorption configurations when the molecular films are grown on a solid surface. Inelastic electron tunneling spectroscopy with scanning tunneling microscope (STM-IETS) is a powerful technique to observe the vibrational states of atoms or molecules on solid surfaces. At present, most STM-IETS works have been conducted at liquid helium temperature (~4K) due to the measurement technique constraints. However, measuring the phonons at high temperature is needed for evaluating the anharmonicity and will provide crucial information on coupling between phonons and their effect. In this work, we have succeeded in measuring the IETS spectra of iron (II) phthalocyanine (FePc) 2D lattice grown on Au (111) at 77 K. The STM topography image illustrated the clear growth of the 1st monolayer (ML) and 2nd ML of FePc. The spectrum of the 1st ML of FePc shows no significant peaks. On the other hand, several peaks appeared in the spectra of the 2nd ML of FePc because of the reduction of hybridization with Au substrate, which is consistent with the lower temperature measurements. And the peak position essentially corresponds to the respective vibrational mode of FePc. We believe that the results open a possibility of phonon studies at higher temperature with high spatial resolution.

Keywords: STM-IETS, 2D FePc Growth, Vibrational Energies, 77 K, 2D materials