an international team of researchers, led by alexander balandin at the university of california at riverside, has announced a modification to the energy spectrum of acoustic phonons, confining them to nanoparticle-scale semiconductor structures, which could allow scientists to tune the thermal properties of semiconductor materials for better heat dissipation in nanoscale electronics.

alexander balandin led a team of researchers that modified the energy spectrum of phonons. (uc-riverside)

as electronic devices continue to get smaller and the component density continues to rise, scientists have been looking for a breakthrough to improve thermal management on a nanoscale. according to a report on the uc-riverside website, the researchers are hoping that this will be a way to control phonons and get past any size restrictions for electronic design.

using semiconductor nanowires made of gallium arsenide (gaas) that were synthesized in finland and an imaging technique called brillouin-mandelstam light scattering spectroscopy (bms), researchers were able to examine the movement of phonons, which are elemental excitations that can spread heat easily through crystalline material.

the researchers adjusted the size and shape of the nanowires and changed the dispersion of the acoustic phonons. this showed that scientists could control the energy spectrum of phonons at a nanoscale.

“for years, the only envisioned method of changing the thermal conductivity of nanostructures was via acoustic phonon scattering with nanostructure boundaries and interfaces,” balandin said. “we demonstrated experimentally that by spatially confining acoustic phonons in nanowires one can change their velocity, and the way they interact with electrons, magnons, and how they carry heat. our work creates new opportunities for tuning thermal and electronic properties of semiconductor materials.”

the work was published online in nature communications on november 10. the abstract of the report stated:

“similar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. however, despite strong scientific and practical importance, conclusive experimental evidence of confined acoustic phonon polarization branches in individual free-standing nanostructures is lacking.

“here we report results of brillouin—mandelstam light scattering spectroscopy, which reveal multiple (up to ten) confined acoustic phonon polarization branches in gaas nanowires with a diameter as large as 128 nm, at a length scale that exceeds the grey phonon mean-free path in this material by almost an order-of-magnitude. the dispersion modification and energy scaling with diameter in individual nanowires are in excellent agreement with theory.

“the phonon confinement effects result in a decrease in the phonon group velocity along the nanowire axis and changes in the phonon density of states. the obtained results can lead to more efficient nanoscale control of acoustic phonons, with benefits for nanoelectronic, thermoelectric and spintronic devices.”

read the full report at http://www.nature.com/articles/ncomms13400.