Chiral honeycomb lattices of non-planar π-conjugated supramolecules on a Ag(111) surface

Ryohei Nemoto^1,2*, Saya Nakano³, Masahisa Tsuchiizu³, Ryuichi Arafune², Noriaki Takagi⁴, Rie Suizu^5,6,7, Takashi Uchihashi^2,8, Kunio Awaga^6,9

¹Department of Physics, Science Tokyo, Tokyo, Japan
²MANA, National Institute for Materials Science, Ibaraki, Japan
³Department of Physics, Nara Women’s University, Nara, Japan
⁴Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
⁵Synchrotron Light Application Center, Saga University, Saga, Japan
⁶Department of Chemistry and IRCCS, Nagoya University, Nagoya, Japan
⁷Japan Science and Technology Agency, PRESTO, Saitama, Japan
⁸Graduate School of Science, Hokkaido University, Sapporo, Japan
⁹National Institute of Technology (KOSEN), Toyota College, Aichi, Japan

* Presenter:Ryohei Nemoto, email:nemoto@phys.sci.isct.ac.jp

In recent years, molecular two-dimensional structures on metal surfaces have been actively investigated in the field of organic molecular electronics and spintronics. Organic molecules on metal surfaces forms self-assemble structures that differ from the bulk due to the presence of molecular-substrate interactions in addition to intermolecular interactions. In particular, the honeycomb lattices are two-dimensional structures with strongly isotropic lattices proposed by graph theory, and their physical properties have been evaluated in various fields.
In this study, we discuss about the structural and electronic properties of self-assembled organic molecular monolayers on Ag(111) surfaces, focusing on the C3 Y-shape triptycene derivative: Trip-Phz by means of scanning tunneling microscopy (STM) measurements, tight binding (TB) calculations and density functional theory (DFT) calculations.
Trip-Phz molecules have been found to form a honeycomb lattice in crystals recrystallized from TTF solutions [1], while in single crystals they adopt a close-packed structure. Trip-Phz honeycomb lattice is also expected to develop a Kagome lattice-derived band structure formed from the C3 symmetry of the molecule and the honeycomb lattice symmetry of the crystal structure. The electronic structure of Kagome lattices has not only Dirac bands but also flat bands. This specific band structure has attracted much attention as it has been discussed to strongly correlated phenomena such as superconductivity, ferromagnetism and the anomalous quantum Hall effect.
We deposited Trip-Phz molecules on Ag(111) surfaces in ultra-high vacuum and measured sub-monolayer films by means of a low temperature STM. We observed that the Trip-Phz molecules self-assemble into chiral honeycomb l
attices on the Ag(111) surfaces. Furthermore, theoretical calculation results (TB and DFT) indicate the presence of a band structure characteristic of a Kagome lattice.
In this presentation, we will provide a detailed analysis of the band structure of Trip-Phz honeycomb system. Additionally, we discuss about the possibility of realizing an artificial Dirac band by molecular network. This work has previously been published in ACS nano [2].
[References]
[1] R. Ushiroguchi, Y. Shuku, R. Suizu, and K. Awaga, Cryst. Growth Des., 20, 7593 (2020)
[2] R. Nemoto, R. Arafune, S. Nakano, M. Tsuchiizu, N. Takagi, R. Suizu, T. Uchihashi and K. Awaga, ACS nano, 18, 30, 19663-19671(2024)

Keywords: honeycomb lattice, Kagome lattice, molecular film, scanning tunneling microscopy