Vibration Spectra of 2D Molecular Lattice at 77K

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

¹Electrophysics, National 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.ep08g@nctu.edu.tw

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 [1]. 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 electron and phonons and its 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 first and second layer of FePc. The spectrum of the first layer of FePc shows no significance peaks. On the other hand, several peaks appeared in the spectra of the second layer of FePc because of the reduction of hybridization with Au substrate, which is consistent with the lower temperature measurements [2]. 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.

References:
[1] B. C. Stipe et al., Science 280, 1732 (1998).
[2] N. Ohta et al., J. Phys. Chem. C 117, 21832 (2013).

Keywords: STM-IETS, Phonon, FePc