TY - JOUR
T1 - Two-Dimensional Phononic Crystals: Disorder Matters
AU - Wagner, Markus R.
AU - Graczykowski, Bartlomiej
AU - Reparaz, Juan Sebastian
AU - El Sachat, Alexandros
AU - Sledzinska, Marianna
AU - Alzina, Francesc
AU - Sotomayor Torres, Clivia M.
PY - 2016/9/14
Y1 - 2016/9/14
N2 - © 2016 American Chemical Society. The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.
AB - © 2016 American Chemical Society. The design and fabrication of phononic crystals (PnCs) hold the key to control the propagation of heat and sound at the nanoscale. However, there is a lack of experimental studies addressing the impact of order/disorder on the phononic properties of PnCs. Here, we present a comparative investigation of the influence of disorder on the hypersonic and thermal properties of two-dimensional PnCs. PnCs of ordered and disordered lattices are fabricated of circular holes with equal filling fractions in free-standing Si membranes. Ultrafast pump and probe spectroscopy (asynchronous optical sampling) and Raman thermometry based on a novel two-laser approach are used to study the phononic properties in the gigahertz (GHz) and terahertz (THz) regime, respectively. Finite element method simulations of the phonon dispersion relation and three-dimensional displacement fields furthermore enable the unique identification of the different hypersonic vibrations. The increase of surface roughness and the introduction of short-range disorder are shown to modify the phonon dispersion and phonon coherence in the hypersonic (GHz) range without affecting the room-temperature thermal conductivity. On the basis of these findings, we suggest a criteria for predicting phonon coherence as a function of roughness and disorder.
KW - Phononic crystals
KW - coherence
KW - disorder
KW - order
KW - roughness
KW - thermal conductivity
UR - https://ddd.uab.cat/record/212892
U2 - https://doi.org/10.1021/acs.nanolett.6b02305
DO - https://doi.org/10.1021/acs.nanolett.6b02305
M3 - Article
VL - 16
SP - 5661
EP - 5668
JO - Nano Letters
JF - Nano Letters
SN - 1530-6984
IS - 9
ER -