MIT Models Bismuth-Antimony Properties
MIT researchers said thin films of bismuth-antimony have electronic properties that are highly desirable for next-generation ICs or thermoelectric generators and coolers.
The compound forms two-dimensional Dirac cones, the cone-shaped graph plotting energy versus momentum for electrons moving through the material.
The research, carried out by materials science and engineering PhD candidate Shuang Tang and Professor Mildred Dresselhaus, appears in the journal Nano Letters. Dresselhaus said the initial analysis was based on theoretical modeling of the bismuth-antimony film’s properties, and it will take about a year to test samples.
Tang said models show that electrons “can travel like a beam of light” through the bismuth-antimony compound, in some cases hundreds of times faster than in silicon. “In a thermoelectric application — where a temperature difference between two sides of a device creates a flow of electrical current — the much faster movement of electrons, coupled with strong thermal insulating properties, could enable much more efficient power production,” MIT said in a detailed report on the effort.
Self Assemby of Nanoparticles
Scientists based at the Lawrence Berkeley National Laboratory and the University of California Berkeley said they have directed the first self-assembly of nanoparticles into device-ready materials. A Berkeley Lab report said the researchers produced multiple-layers of thin films from highly ordered one-, two- and three-dimensional arrays of gold nanoparticles, using a relatively inexpensive technique based on blending nanoparticles with block co-polymer supramolecules.
A supramolecule is a group of molecules that act as a single molecule able to perform a specific set of functions, while block copolymers are long sequences or “blocks” of one type of monomer bound to blocks of another type of monomer that have an innate ability to self-assemble into well-defined arrays of nano-sized structures over macroscopic distances, the report said.
“Block copolymer supramolecules self-assemble and form a wide range of morphologies that feature microdomains typically a few to tens of nanometers in size,” Berkeley Lab scientist Ting Xu said. “As their size is comparable to that of nanoparticles, the microdomains of block copolymer supramolecules provide an ideal structural framework for the co-self-assembly of nanoparticles.”
The inter-particle distance between gold nanoparticles in the 1-D chains and the 2-D sheets was 8 to 10 nanometers, which may create opportunities in plasmonics, the phenomenon by which a beam of light is confined in ultra-confined spaces.
“Our gold thin films display strong plasmonic coupling along the inter-particle spacing in the 1-D chains and 2-D sheets respectively,” Xu says. “We should therefore be able to use these films to investigate unique plasmonic properties for next-generation electronic and photonic devices. Our supramolecular technique might also be used to fabricate plasmonic metamaterials.”
– by David Lammers