Direct observation of confined acoustic phonon polarization branches in free-standing semiconductor nanowires.
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.
Phonon Optimized Engineered Materials (POEM) Center and Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, California 92521, USA.
Fariborz
0000-0003-2192-2023
F
Kargar
Laboratory for Terascale and Terahertz Electronics (LATTE), Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, California 92521, USA.
Bishwajit
B
Debnath
Department of Micro and Nanosciences, School of Electrical Engineering, Aalto University, PO Box 13500, 00076 Aalto, Finland.
Joona-Pekko
JP
Kakko
Department of Micro and Nanosciences, School of Electrical Engineering, Aalto University, PO Box 13500, 00076 Aalto, Finland.|Institute of Photonics, University of Eastern Finland, FI-80101 Joensuu, Finland.
Antti
A
Säynätjoki
Department of Micro and Nanosciences, School of Electrical Engineering, Aalto University, PO Box 13500, 00076 Aalto, Finland.
Harri
0000-0003-2487-4645
H
Lipsanen
Phonon Optimized Engineered Materials (POEM) Center and Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, California 92521, USA.|Department of Physics and Engineering, Moldova State University, Chisinau MD 2009, Republic of Moldova.
Denis L
DL
Nika
Laboratory for Terascale and Terahertz Electronics (LATTE), Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, California 92521, USA.|Spins and Heat in Nanoscale Electronic Systems (SHINES) Center, University of California-Riverside, Riverside, California 92521, USA.
Roger K
RK
Lake
Phonon Optimized Engineered Materials (POEM) Center and Department of Electrical and Computer Engineering, University of California-Riverside, Riverside, California 92521, USA.|Spins and Heat in Nanoscale Electronic Systems (SHINES) Center, University of California-Riverside, Riverside, California 92521, USA.
Alexander A
AA
Balandin