Effects of medium range order on propagon thermal conductivity in amorphous silicon

Abstract

We discuss the dependence of the propagon contribution to thermal conductivity on the medium range order (MRO) in amorphous silicon. Three different amorphous structures with the same size of 3.28 nm were studied. Among these three structures, two structures were constructed with experimentally observed MRO [Treacy and Borisenko, Science. 335, 6071 (2012)] and the other structure is from continuous random network (CRN), which lacks MRO and thus represents a randomized amorphous structure [Barkema and Mousseau, Physical Review B, 62, 8 (2000)].Using the simulated fluctuation electron microscopy and dihedral angle distribution, we confirm that the first two structures contain MRO in the length scale of 10-20 Å while the CRN structure does not. The transport of propagons in the MRO and CRN structures are compared using the dynamic structural factor calculation and normal mode decomposition of the molecular dynamics simulation data, showing noticeably longer lifetime of propagons in the MRO structures than in the CRN structure. The propagon thermal conductivity in the MRO structures is estimated 50% larger than that in the CRN structure.

Enhancement of short/medium-range order and thermal conductivity in ultrahard sp3 amorphous carbon by C70 precursor

“…Among them, the low-frequency propagons, resembling phonons in crystalline solids, have relatively large mean free paths and high heat transfer efficiency 52 . Previous theoretical simulation results have shown that an amorphous material with higher MRO exhibits larger thermal conductivity as the propagon thermal conductivity in a MRO structure is larger than that in an ideal amorphous structure 13 . This is the reason why the current sp 3 amorphous carbon with higher local structural order exhibits such a high thermal conductivity.…”

Examining normal modes as fundamental heat carriers in amorphous solids: the case of amorphous silicon

“…With these three widely used normal mode methods reviewed, we reiterate here what the normal mode methods predict of thermal transport in amorphous silicon [12,[17][18][19][20][21].…”

“…The literature on normal mode descriptions of a-Si has some variations in detailed conclusions, but the general consensus is that propagons contribute from 20 to 50 % of overall thermal conductivity despite their small population consisting of only ∼ 3 % of the density of states [8,12,[17][18][19][20][21], and that they are dominantly scattered by anharmonicity [12,17,18].…”