Rensselaer Researchers Make Composite Nanorods With Tree-Like "Branches"
Researchers at Rensselaer Polytechnic Institute announced a new technique for growing single-crystal nanorods and controlling their shape using biomolecules that could enable the development of smaller, more powerful heat pumps and devices that harvest electricity from heat. The researchers have discovered how to direct the growth of nanorods made up of two single crystals using a biomolecular surfactant. The researchers were also able to create "branched" structures by carefully controlling the temperature, time, and amount of surfactant used during synthesis.
"Our work is the first to demonstrate the synthesis of composite nanorods with branching, wherein each nanorod consists of two materials – a single-crystal bismuth telluride nanorod core encased in a hollow cylindrical shell of single-crystal bismuth sulfide," said G. Ramanath, Professor of Materials Science and Engineering at Rensselaer and Director of the university’s Center for Future Energy Systems, who led the research project. "Branching and core-shell architectures have been independently demonstrated, but this is the first time that both features have been simultaneously realized through the use of a biomolecular surfactant."
Most nanostructures comprised of a core and a shell generally require more than one step to synthesize, but these new research results are said to demonstrate how to synthesize such nanorods in only one step. Because of their attractive properties, core-shell nanorods are expected to one day enable the development of new nanoscale thermoelectric devices for power generation, as well as nanoscale heat pumps for cooling hot spots in nanoelectronics devices.
The researchers discovered that synthesis at high temperatures or with low amounts of the biomolecular surfactant L-glutathonic acid (LGTA) yields branched nanorod structures in highly regulated patterns. In contrast, synthesis at low temperatures or with high levels of LGTA results in straight nanorods without any branching. It is interesting to note that at the point of branching, atoms in the branch resemble a mirror image of the parent crystal – a finding that reinforces the researchers’ conclusion that LGTA is able to induce branching through atomic-level sculpture.
