Nanotechnology

Physicists use selenium doping to achieve high selectivity in nanostructures

Scanning tunneling microscope image of the reaction pathway of mTBPT on a Cu(111) substrate, showing the transition from a random metal-organic structure before selenium doping to a well-ordered, crystalline, two-dimensional metal-organic nanostructure after doping. Credit: Nature Communications (2024). DOI: 10.1038/s41467-024-47614-9

Physicists at the National University of Singapore (NUS) have used flexible precursors and selenium doping to achieve controlled conformations of nanostructures, enhancing material properties and structural uniformity, a method that advances surface synthesis for the design and development of engineered nanomaterials.

The research results were published in the journal Nature Communications.

Surface synthesis has been extensively studied over the past few decades due to its ability to generate diverse nanostructures. Through judicious design of precursors, selection of substrates, and precise control of experimental parameters such as molecular concentration, electrical stimulation, and thermal treatment, a wide variety of complex nanostructures have been achieved.

Among these methods, Ullmann coupling is noteworthy for efficiently coupling precursors via dehalogenation and covalent bonding. Although most studies have focused on structurally rigid precursors, studying structurally flexible precursors offers great potential for developing complex functional nanomaterials with designed structures and properties.

Research led by Professor Andrew Wee from the NUS Department of Physics has demonstrated the topological selectivity of the structurally flexible precursor mTBPT using selenium (Se) doping, which features a triazine ring with three metabromophenyl groups and exhibits conformers with C3h and Cs symmetry.

Conformers are molecules that have the same molecular formula and atomic connectivity, but differ in the spatial arrangement of their atoms due to rotations around single bonds. When deposited on a copper (Cu(111)) substrate, a random mixture of these conformers is initially formed.

By doping with 0.01 monolayer Se at temperatures ranging from room temperature to 365 Kelvin, the researchers achieved high selectivity for the C3h conformer, which significantly improved the structural uniformity and led to the formation of well-ordered two-dimensional metal-organic frameworks (MOFs). The process was valid regardless of the deposition order of mTBPT and Se.

“We combined high-resolution scanning tunneling microscopy and spectroscopy at a low temperature of 4 Kelvin with non-contact atomic force microscopy to study the formation of the structurally flexible precursor mTBPT on copper substrates and its high topological selectivity upon selenium doping,” said Dr. Cai Liangliang, a research associate on the team.

The team also used density functional theory calculations with and without Se to model the conversion between Cs−Cu and C3h−Cu moieties on a Cu(111) substrate and explained the high topological selectivity of the C3h conformer upon Se doping.

“Given the growing interest in two-dimensional selenides and surface synthesis, understanding the doping effect, and in particular selenium doping, is important. This insight may lead to the controllable synthesis of tailored metal-organic and covalent organic framework nanostructures in future,” added Professor Wee.

Further information: Liangliang Cai et al. “Topological selectivity of conformationally flexible precursors by selenium doping.” Nature Communications (2024). DOI: 10.1038/s41467-024-47614-9

Provided by National University of Singapore

Citation: Physicists Use Selenium Doping to Achieve High Selectivity in Nanostructures (September 16, 2024) Retrieved September 17, 2024 from https://phys.org/news/2024-09-physicists-high-nanostructures-selenium-doping.html

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