Cadmium-based nanostructures are ideal, for example, for the development of two-dimensional materials that interact specifically with light in the near infrared (NIR) by either absorbing, reflecting, emitting or exhibiting other optical properties. This spectral range is of interest for numerous technologies. In medical diagnostics, for example, such materials enable deeper insights into tissue, as NIR light is scattered less than visible light. In communications technology, NIR materials are used in highly efficient fiber optic systems, while in solar energy they can potentially increase the efficiency of photovoltaic cells.
“The decisive factor for all these applications is the ability to specifically modify the material so that it has the desired optical and electronic properties,” says Dr. Rico Friedrich from the Institute of Ion Beam Physics and Materials Research at the HZDR and the Chair of Theoretical Chemistry at TU Dresden. “This used to be problematic, because nanochemical synthesis work was usually more like mixing and trying, adds Prof. Alexander EychmĂĽller from the Chair of Physical Chemistry at TU Dresden. Both scientists jointly led the cooperative research project.
Innovative approach: cation exchange for the production of well-defined nanoparticles
The particular challenge here is to control the number of atomic layers and their composition in the nanostructures – and thus the thickness – in a targeted manner without changing their width and length. The synthesis of such complex nanoparticles is a key challenge in materials research. This is where cation exchange comes in, a method in which certain cations – positively charged ions – in a nanoparticle are specifically replaced by others. “The process allows precise control of the composition and structure, so that particles can be produced with properties that would not be possible using conventional synthesis methods. Nevertheless, little is known about how exactly this reaction takes place and at what point it begins,” says EychmĂĽller.
In the team’s current work, the focus was on nanoplatelets whose active corners play a decisive role. These corners are chemically particularly reactive and enable the platelets to link together to form organized structures. In order to better understand these effects, the researchers combined sophisticated synthetic methods, atomic-resolution (electron) microscopy and extensive computer simulations.
Active corners and defects in nanoparticles are not only interesting for their chemical reactivity, but also for their optical and electronic properties. At these points, there is often a concentration of charge carriers, which can influence charge carrier transport and light absorption. “In combination with the ability to exchange individual atoms or ions, such defects could also be used in single-atom catalysis. Here, the high reactivity and selectivity of individual atoms is used to make chemical processes more efficient,” explains Friedrich. The precise control of such defects is also crucial for the NIR activity of nanomaterials. They influence how light is absorbed, emitted or scattered in the near infrared and therefore offer starting points for specifically optimizing the optical properties.
Linking nanostructures: a step towards self-organization
Another result of this research is the possibility of specifically linking the nanoplatelets. The active corners allow the particles to be combined into ordered or even self-organized structures. This organization could be used in future applications to create complex materials with integrated functions, for example for NIR-active sensors or new types of electronic components. In practice, such materials could increase the efficiency of sensors and solar cells or enable new ways of data transmission. At the same time, the research provides fundamental insights that are also important for other areas of nanoscience, such as catalysis or the development of quantum materials.
The team’s findings were only made possible by combining state-of-the-art synthetic, experimental and theoretical methods. The researchers were not only able to precisely control the structure of the nanoparticles, but also investigate the role of the active corners in detail. Experiments on atomic defect distribution and compositional analysis were combined with theoretical modeling to obtain a comprehensive understanding of the material properties.
Publication
V. Shamraienko, R. Friedrich, S. Subakti, A. Lubk, A. V. Krasheninnikov, A. EychmĂĽller, Weak Spots in Semiconductor Nanoplatelets: From Isolated Defects Toward Directed Nanoscale Assemblies, in Small, 2024 (DOI: 10.1002/smll.202411112)
Contact
Dr. Rico Friedrich
Institute of Ion Beam Physics and Materials Research at the HZDR
& Chair of Theoretical Chemistry at the TU Dresden
Tel.: +49 351 260 3718 | E-Mail: r.friedrich@hzdr.de
Prof. Alexander EychmĂĽller
Professorship of Physical Chemistry at the TU Dresden
Tel.: +49 351 463 39843 | E-Mail: Alexander.Eychmueller@tu-dresden.de
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Further links
👉 www.hzdr.de
Photo: B. Schröder/HZDR
