Cadmium-based nanostructures are opening new possibilities in near-infrared (NIR) technology, from medical imaging to fiber optics and solar energy.
A major challenge in their development is controlling their atomic structure with precision, which researchers at HZDR and TU Dresden tackled using cation exchange. This technique allows for precise manipulation of nanostructure composition, unlocking new optical and electronic properties. The research highlights the crucial role of active corners and defects, which influence charge transport and light absorption. By linking these nanostructures into organized systems, scientists are paving the way for self-assembling materials with advanced functions, from improved sensors to next-generation electronics.
Harnessing Near-Infrared Light with Cadmium-Based Nanostructures
Cadmium-based nanostructures play a key role in developing two-dimensional materials that interact with near-infrared light (NIR) by absorbing, reflecting, or emitting it. These interactions make them valuable for various technologies. In medical diagnostics, NIR light penetrates tissue more effectively than visible light, providing clearer imaging. In telecommunications, NIR materials enhance fiber-optic systems, improving data transmission efficiency. In solar energy, they have the potential to boost photovoltaic cell performance.
“The ability to specifically modify the material to present the desired optical and electronic properties is crucial for all these applications,” says Dr. Rico Friedrich from the Institute of Ion Beam Physics and Materials Research at HZDR and Chair of Theoretical Chemistry at TU Dresden. “In the past, this was a challenge because nanochemical synthesis used to be more about mixing materials by trial and error,” adds Prof. Alexander Eychmüller, Chair of Physical Chemistry at TU Dresden. The two scientists jointly led the collaborative research project.
An Innovative Approach: Cation Exchange for Precise Nanoparticle Control
One of the main challenges in nanomaterial research is controlling the thickness of nanostructures by adjusting their atomic layers while maintaining their width and length. Traditional synthesis methods struggle to achieve this precision. Cation exchange offers a solution by systematically replacing certain positively charged ions (cations) in a nanoparticle with others.
“The process gives us precise control over the composition and structure, allowing us to produce particles with properties that we could not attain using conventional synthesis methods. However, little is known about the exact workings and starting point of this reaction,” says Eychmüller.
The Role of Active Corners and Defects
In the current project, the team focused on nanoplatelets, whose active corners play a crucial role. These corners are particularly chemically reactive, which makes it possible to bind the platelets into organized structures. 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 because of their chemical reactivity, but also their optical and electronic properties. These places often have a high concentration of charge carriers, which can affect their transport and the absorption of light. “Combined with an ability to exchange single atoms or ions, we could also use such defects in single-atom catalysis, harnessing the high reactivity and selectivity of individual atoms to increase the efficiency of chemical processes,” explains Friedrich. Precise control of such defects is also crucial for the NIR activity of nanomaterials. They affect how near-infrared light is absorbed, emitted, or scattered, offering ways to systematically optimize optical properties.
Self-Organizing Nanostructures: A New Frontier in Materials Science
Another outcome of this research is the possibility to systematically link nanoplatelets by their active corners, combining the particles into ordered or even self-organized structures. Future applications could use this organization to produce complex materials with integrated functions, such as NIR-active sensors or new types of electronic components. In practice, such materials could increase the efficiency of sensors and solar cells or facilitate new methods of data transmission. At the same time, the research also generates fundamental insights for other areas of nanoscience, such as catalysis or quantum materials.
Unraveling Material Properties Through Advanced Techniques
The team’s findings were only possible thanks to a combination of 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 gain a comprehensive understanding of the material properties.
Reference: “Weak Spots in Semiconductor Nanoplatelets: From Isolated Defects Toward Directed Nanoscale Assemblies” by Volodymyr Shamraienko, Rico Friedrich, Subakti Subakti, Axel Lubk, Arkady V. Krasheninnikov and Alexander Eychmüller, 18 December 2024, Small.
DOI: 10.1002/smll.202411112
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