RESEARCH NEWS STORY
January 31, 2024
Chiba University

Small Yet Mighty: Showcasing Precision
Nanocluster Formation with Molecular Traps
Researchers demonstrate the growth of cobalt nanoclusters on two-dimensional copper
surfaces using an array of ring-shaped crown ether molecules
Nanoclusters (NCs) of transition metals like cobalt or nickel have widespread applications
in drug delivery and water purification, with smaller NCs exhibiting improved functionalities.
Downsizing NCs is, however, usually challenging. Now, scientists from Chiba University inJapan have demonstrated functional NC formation with atomic-scale precision. They
successfully grew cobalt NCs on flat copper surfaces using molecular arrays as traps. This
breakthrough paves the way for advancements like single-atom catalysis and spintronics
miniaturization.

Image title: Room Temperature Precision Formation of Cobalt Nanoclusters.

Image caption: Researchers demonstrates the successful formation of functional
nanoclusters using cobalt atom deposition on two-dimensional arrays of crown ether ringmolecules.
Image credit: Masaki Horie from National Tsing Hua University
Image license: Original content
Nanoclusters (NCs) are crystalline materials that typically exist on the nanometer (10-9 m)
scale. They are composed of atoms or molecules in combination with metals like cobalt, nickel,
iron, and platinum, and have found several interesting applications across diverse fields,
including drug delivery, catalysis, and water purification. A reduction in the size of NCs canunlock additional potential, allowing for processes such as single-atom catalysis. In thiscontext, the coordination of organic molecules with individual transition-metal atoms shows
promise for further advancement in this field.
An innovative approach to further reduce the size of NCs involves introducing metal atoms
into self-assembled monolayer films on flat surfaces. However, it is crucial to exercise caution
in ensuring that the arrangement of metal atoms on these surfaces does not disrupt theordered nature of these monolayer films. Now, in a recent study featured in the Journal ofMaterials Chemistry C, Dr. Toyo Kazu Yamada from the Graduate School of Engineering at
Chiba University, along with Masaki Horie from the Department of Chemical Engineering at
National Tsing Hua University, Satoshi Kera from the Institute for Molecular Science, andPeter Krüger also from the Graduate School of Engineering at Chiba University, haveshowcased the surface growth of cobalt atoms on molecular ring arrays at room temperature.
Talking to us about this advancement. Dr. Yamada says, "This advanced method of functional
nanocluster formation with atomic-scale precision can be utilized in the development of highly
efficient catalysts or in quantum computing."
In the study, the team used ring-shaped molecular structures called "crown ethers," whichcontain benzene and bromine rings. These structures were used to trap and grow cobalt NCs
on flat copper surfaces. The resulting cobalt NCs were of two sizes, 1.5 nm and 3.6 nm. To
understand their properties and structure further, various techniques were employed,
including low-temperature scanning tunneling microscopy and spectroscopy (STM and STS),
angle-resolved photoelectron spectroscopy (ARPES) with low energy electron diffraction(LEED), and density functional theory (DFT) calculations.
The analysis revealed the formation of stable surface sites to which the cobalt atoms could
attach. In addition, the formation of these stable surface sites was found to be influenced by
the electronic hybridization (mixing) between the crown ethers and cobalt. Once the cobalt
atom was trapped, it acted like a nucleation center, attracting other cobalt atoms to form anNC. Additionally, unlike the usual behavior of crown ether molecules in solution, thesemolecules did not trap the metal atom at the center of the crown ring. Instead, the metal
atom was at the edge, because of the presence of bromine atoms at that location. Discussing
the long-term potential of these findings, Dr. Yamada says, "The use of this approach inapplications such as single-atom catalysis, miniaturization of spintronics media, and quantum
computing will contribute to the development of an information-based society in a way that
reduces carbon dioxide (CO2) production."In summary, the team successfully demonstrated the growth of cobalt NCs by exploiting thetrapping potential of two-dimensional crown ether molecules on a copper surface. The
chemical behavior of the crown ether molecules deviated from typical interactions observedin solution, by trapping cobalt atoms at the edge, and not the center. Importantly, the method
demonstrated effective and large-scale production of NCs with well-defined size andmorphology at room temperature.
Funding:
This work was supported by JSPS KAKENHI grant numbers 17K19023 and 23H02033, theMurata Science Foundation, the Shorai Foundation for Science and Technology, TEPCO
Memorial Foundation, Casio Science Promotion Foundation, and Toshiaki Ogasawara
Memorial Foundation.
Reference:
Title of original paper: On-surface growth of transition-metal cobalt nanoclusters using a 2D
crown-ether arrayAuthors:

Toyo Kazu Yamada1,2, Ryohei Nemoto1, Fumi Nishino1, Takuya Hosokai3, ChiHsien Wang4, Masaki Horie4, Yuri Hasegawa5, Satoshi Kerae5, and Peter
Krüger1,2Affiliations:

1Department of Materials Science, Chiba University
2Molecular Chirality Research Centre, Chiba University
3National Metrology Institute of Japan, National Institute of Advanced

Industrial Science and Technology
4Department of Chemical Engineering, National Tsing Hua University
5Institute for Molecular Science
Journal:Journal of Materials Chemistry C

DOI:

10.1039/d3tc03339b

Contact: Toyo Kazu Yamada
Graduate School of Engineering, Department of Materials Science, Chiba University
Email: toyoyamada@faculty.chiba-u.jp
Public Relations Office, Chiba University
Address: 1-33 Yayoi, Inage, Chiba 263-8522 JAPAN
Email: koho-press@chiba-u.jp
Tel: +81-43-290-2018

Additional information for EurekAlert:Latest Article Publication Date: 11 December 2023
Method of Research: Experimental study
Subject of Research: Not applicable
Conflict of Interest (COI) Statement: There are no conflicts to declare.
Keywords:
Primary: Applied Sciences and Engineering
Secondary: Nanofabrication, Nanostructures, Nanoclusters, Self-Assembly, Monolayers,Catalysis, Transition Metals, Cobalt, Copper, Surface Chemistry