Cation Exchange Reaction Altering Nanowires into Nano-Tools
A breakthrough was made recently at the University of Pennsylvania where, a team of engineers managed to achieve the transformation of simple nanowires into reconfigurable materials and circuits. The importance of this experiment was that it single handedly showed that a novel, self-assembling method for chemically creating nanoscale structures is possible.
The research team, utilizing only chemical reactants, brought about the transformation of semiconducting nanowires into a wide variety of useful, nanoscale materials that included nanoscale metal strips with periodic stripes and semiconducting designs, strictly metal nanowires, radial heterostructures and hollow semiconducting nanotubes. Other compositions and morphologies were also involved.
Future applications of nanomaterials in electronics, catalysis, photonics and bionanotechnology are driving the exploration of synthetic approaches to control and manipulate the chemical composition, structure and morphology of these materials. To realize their full potential, it is preferable to evolve methods that can transform nanowires into tunable but precisely controlled morphologies, particularly in the gas-phase, to be compatible with nanowire growth systems. The assembly, however, is a high-priced and labor-intensive process that prohibits cost-effective production of these materials.
Researchers utilized ion exchange, which is one of the two most basic methods for solid phase transformation of nanostructures. Ion (cation/anion) exchange reactions exchange positive or negative ions and have been utilized to change the chemical composition of inorganic nanocrystals, as well as create semiconductor superlattice structures. It is the chemical process, for example, that turns hard water soft in many American homes.
In this study, researchers transformed single-crystalline cadmium sulfide nanowires into composition-controlled nanowires, core?shell heterostructures, metal-semiconductor superlattices, single-crystalline nanotubes and metallic nanowires by using size-dependent cation-exchange reactions along with temperature and gas-phase reactant delivery control. This versatile, synthetic ability to transform nanowires offers new opportunities to analyze size-dependent phenomena at the nanoscale and tune their chemical/physical properties to design reconfigurable circuits.
Researchers also determined that the speed of the cation exchange procedure was ascertained by the size of the starting nanowire and that the process temperature impacted the final product, adding new information to the conditions that affect reaction rates and assembly.
The central revelation in this research is an additional clarification of the nanoscale chemical phenomena. The study also provides new data on how manufacturers can assemble these tiny circuits, electrically connecting nanoscale structures through chemical self-assembly.
Recent research in the field has enabled the shift of nanomaterials via solid-phase chemical reactions into nonequilibrium, or functional structures that cannot be obtained otherwise.
It also opens up new possibilities for the transformation of nanoscale materials into the tools and circuits of the future, for example, self-assembling nanoscale electrical contacts to individual nanoscale components, smaller electronic and photonic devices such as a series of electrically connected quantum dots for LEDs or transistors, as well as improved storage capacities for batteries.
The study was conducted by Bin Zhang, Yeonwoong Jung, Lambert Van Vug and Agarwal of the Department of Materials Science and Engineering in Penn’s School of Engineering and Applied Science.
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