The Korean Academy of Science and Technology said on Monday that researchers from the Korean Academy of Science and Technology (KAIST) and Ewha Womans University have used atom probe tomography to reveal the three-dimensional distribution of ligand molecules on the surface of nanoparticles.

Capping ligands are organic molecules that appear during the synthesis of metal nanoparticles (NP). It can prevent NP agglomeration and control the size, shape and function of NP. Its importance is becoming more and more important in the synthesis and design of NPs.

The research was published in the online edition of the journal Nature Communications on July 14 under the title "Three-dimensional atomic mapping of ligands on palladium nanoparticles by atom probe tomography."

Professor Choi Pyuck-pa from the Department of Materials Science and Engineering at KAIST and Professor Lee Sang-heon from the Department of Chemical Engineering and Materials Science at Ewha Womans University led the joint research. Chang Kyu-seon, KAIST PhD student, Ph.D. Kim Se-ho of Max-Planck-Institut in Germany co-authored this paper.

Analyzing the spatial distribution of capped ligands composed of organic molecules with complex structures requires techniques with atomic unit spatial resolution, high sensitivity for light element detection, and three-dimensional analysis. Unfortunately, due to the lack of this technology, there has not been a case of three-dimensional observation of the distribution of capped ligands on the surface of nanoparticles. Therefore, the behavior of ligands during particle synthesis remains a mystery to a considerable extent.

For example, it is known that bromide ion, a halide ligand, can promote the formation of cubic metal nanoparticles, but many recent studies have reported different results.

Professor Choi’s team used atomic probe tomography (ATP.

APT reconstructs the 3D atom distribution map of the sample. The atoms on the surface of the needle-shaped sample evaporate under the action of ultra-high vacuum and strong electric field. These vaporized atoms collided into the detector one by one. Use the collision points and atomic order recorded by the detector to compare the mass and current of the collision atoms to obtain a 3D atom map.

Recently, APT that can perform 3D atomic analysis, quantitative chemical analysis, Angstrom unit spatial resolution, and ppm-level detection sensitivity for all atoms has attracted much attention in material analysis.

The research team calculated the density of Cetrimonium ligand present on the surface of each NPs based on the monolayer film data of the 3D distribution of the ligand. Through this research, the team discovered an interaction between Cetrimonium ligand and halide ligand. This interaction between different ligands determines the final shape and antioxidant properties of the nanoparticles. It also explains why the existing research results are inconsistent with each other.

Professor Cui said: “By providing experimental and theoretical results that can contain conflicting existing research results, this research is meaningful.” “We hope that the research results will help to synthesize and apply the basic understanding of NPs. To map NPs with excellent characteristics."