A research team from the University of Vienna and TU Wien has successfully embedded individual platinum atoms into an ultrathin material and, for the first time, pinpointed their positions within the lattice with atomic precision. This breakthrough was achieved using a novel approach that combines defect engineering in the host material, the controlled placement of platinum atoms, and a cutting-edge, high-contrast electron imaging technique known as ptychography. The results, published in Nano Letters, open up new possibilities for the precise tailoring of materials at the atomic scale.
Enhancing the performance of materials for applications such as catalysis (the acceleration of chemical reactions) or selective gas detection requires atomic-level control of their structure. Crucial to this are so-called active centers - tiny sites on the material's surface where chemical reactions occur or gas molecules can specifically bind. These centers are particularly effective when composed of single metal atoms, such as platinum. The current study aimed to produce such materials and simultaneously to precisely visualize their structure at the atomic level.
A Sharp Look into the Atomic Lattice
The host material, molybdenum disulfide (MoS2), is an ultrathin semiconductor with a highly tunable structure. To introduce new active sites, the researchers used helium ion irradiation to deliberately create atomic-scale defects - such as sulfur vacancies - on the MoS2 surface. These vacancy sites were then selectively filled with individual platinum atoms. This precise atomic substitution, known as doping, enables the controlled tuning of the material’s properties for specific applications.
Until now, there was no direct evidence pinpointing the exact positions of the introduced foreign atoms within the atomic lattice, as conventional electron microscopy lacks the contrast needed to clearly distinguish between different defect types, such as single and double sulfur vacancies. Therefore, the researchers employed "Single-Sideband Ptychography" (SSB), a state-of-the-art imaging method based on the analysis of electron diffraction patterns. Lead author David Lamprecht, who initiated the research at the University of Vienna and continued it at TU Wien, emphasizes the significance of this approach: “With our combination of defect engineering, doping, and ptychography, we were able to visualize even subtle differences in the atomic lattice—and clearly determine whether a platinum atom had been incorporated into a vacancy or merely resting loosely on the surface.” Using computer simulations, the various incorporation sites - such as sulfur or molybdenum positions - could be precisely identified, marking a crucial step toward targeted material design.
Two Applications, One Atom
The combination of targeted atom placement and atomically precise imaging opens up new possibilities in two key fields for the future: catalysis and gas sensing. Individual platinum atoms placed at precisely defined sites can act as highly efficient catalysts - for example, in environmentally friendly hydrogen production. At the same time, the material can be tailored to respond only to specific gas molecules. “With this level of control over atom placement, we can develop selectively functionalized sensors - a significant improvement over existing methods,” emphasizes Jani Kotakoski, last author and research group leader at the Faculty of Physics, University of Vienna.
Building Blocks for Functional Materials
This methodological approach is not limited to platinum and MoS2 and can, in principle, be applied to many other combinations of 2D materials and dopant atoms. The team aims to further refine the technique, for instance by achieving more precise control over defect creation or by adding post-treatment steps. The ultimate goal is to create functional materials with tailored properties, where every atom occupies a precisely defined position.
Original Publication:
Uncovering the atomic structure of substitutional platinum dopants in MoS2 with single-sideband ptychography. David Lamprecht, Anna Benzer, Manuel Längle, Mate Capin, Clemens Mangler, Toma Susi, Lado Filipovic, and Jani Kotakoski. In Nano Letters. DOI: 10.1021/acs.nanolett.5c00919
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