International News
This defied everything that they had expected to see , Wu explains . A nanowire ’ s rough surface typically slows phonons down . So , what was going on ?
High-resolution TEM ( transmission electron microscopy ) images of the material captured by Matthew R . Jones and Muhua Sun at Rice University uncovered the first clue : a glass-like layer of silicon dioxide on the silicon-28 nanowire surface .
Computational simulation experiments at the University of Massachusetts Amherst led by Zlatan Aksamija , a leading expert on the thermal conductivity of nanowires , revealed that the absence of isotope “ defects ” – silicon-29 and silicon-30 – prevented phonons from escaping to the surface , where the silicon dioxide layer would drastically slow down the phonons . This in turn kept phonons on track along the direction of heat flow – and therefore less “ confused ” – inside the silicon-28 nanowire ’ s “ core .” ( Aksamija is currently an associate professor of materials science and engineering at the University of Utah .) “ This was really unexpected . To discover that two separate phonon-blocking mechanisms – the surface versus the isotopes , which were previously believed to be independent of each other – now work synergistically to our benefit in heat conduction is very surprising but also very gratifying ,” Wu says .
“ Junqiao and the team discovered a new physical phenomenon ,” Ager says . “ This is a real triumph for curiosity-driven science . It ’ s quite exciting .”
Wu says that the team next plans to take their discovery to the next step : by investigating how to “ control , rather than merely measure , heat conduction in these materials .”
Researchers from Rice University ; the University of Massachusetts-Amherst ; Shenzhen University , and Tsinghua University participated in the study . This work was supported by the DOE Office of Science . RACA
" This is a real triumph for curiosity-driven science . It ’ s quite exciting ."
12
RACA Journal I July 2022 www . refrigerationandaircon . co . za