Designing 2D Molecular Quantum Spin Array on Solid Surfaces

PC Department Seminar
Date: Mar 26, 2025
Time: 11:00 AM (Local Time Germany)
Speaker: Toyo Kazu Yamada
Chiba University, Japan
Location: Building G
Room: 2.06
Host: Akitoshi Shiotari

We aim to control the symmetry of molecular spin structures on solid surfaces and design a two-dimensional (2D) organic quantum bit network with exceptional quantum spin properties. To achieve this, we have employed transition metal atoms and organic molecules as materials. Over the past two decades, we have investigated surface spin structures using scanning tunneling microscopy and spectroscopy (STM/STS), as well as spin-polarized STM/STS, all conducted in ultrahigh vacuum (UHV) at cryogenic temperatures, in combination with density functional theory (DFT) calculations [1-4].

We have first focused on growing well-ordered 2D networks on atomically flat Cu(111) surfaces via Ullmann coupling, using 1,3,5-tris(4-bromophenyl)benzene (TBB) and 4,4’,5,5’-tetrabromodibenzo[18]-crown-6 ether (BrCR) molecules [5-8]. We successfully grew low-dimensional nanonetworks [5] but encountered a key challenge: many intermediate states have formed during the on-surface synthesis, where Cu adatoms are involved in bonding between precursors. This issue led to the forming of a 2D random network, which we could influence by tuning the intermediate states [7]. Consequently, achieving well-ordered growth becomes extremely difficult when additional 3d or 4f magnetic atoms are introduced into this system [8]. This understanding of on-surface synthesis on noble metal surfaces suggests that directly engineered quantum spin structures on such surfaces may not be ideal. Instead, a surface that does not provide active adatoms is required. In other words, atomically flat, epitaxially grown substrate surfaces are necessary.
In this context, we focus on STM imaging of 3d transition metal single atoms and single molecular magnets adsorbed on electronically decoupled thin films prepared on metal substrates: Cu-phthalocyanine (S = 1/2) on insulating MgO films grown on a ferromagnetic Fe(001)-whisker substrate [9], and ammonium-linked ferrocene (Fe²⁺: S = 0 ⇔ Fe³⁺: S ≠ 0) on a BrCR array with trapping capabilities [10]. We also discuss the potential for creating a 2D quantum array on these surfaces.

References:
[1] T. K. Yamada, et al., Physical Review Letters, 90, 056803: 1-4 (2003).
[2] S. Schmaus, T. K. Yamada, Nature Nanotechnology, 6, 185 (2011).
[3] C. G. Ayani, T. K. Yamada, et al., Nanoscale 14, 15111 (2022).
[4] T. Gozlinski, T. K. Yamada, et al., Science Advances 9, eadh9163 (2023).
[5] T. K. Yamada et al., The Journal of Physical Chemistry C, 128, 1477 (2024).
[6] R. Nemoto, T. K. Yamada et al., The Journal of Physical Chemistry C 123, 18939 (2019).
[7] T. K. Yamada et al., Nanoscale Horizons, 9, 718 (2024).
[8] T. K. Yamada et al., Journal of Materials Chemistry C, 12, 874 (2024).
[9] N. K. M. Nazriq, P. Krueger, T. K. Yamada, Applied Surface Science 618, 156628 (2023).
[10] F. Nishino, T. K. Yamada, et al., Small, 202408217 (2024).