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Effect of grain boundaries on thermal transport in graphene
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View: Figures


Image of FIG. 1.
FIG. 1.

Examined graphene GBs constructed using mirror reflection of GNRs with different chiralities: (a) grain-4, (b) grain-7, (c) grain-10, and (d) LD. (e) Example for the chirality of the GNR underlying grain-4.

Image of FIG. 2.
FIG. 2.

Phonon transmission along graphene structures with periodic boundary conditions in the transverse direction (also see Fig. 1 ). (a) Computed dispersion showing phonon energy ℏω vs. wave vector q. L, T, and Z labels correspond to longitudinal, transverse, and out-of-plane phonon displacements. A and O labels are for acoustic and optical phonons, respectively. (b) Corresponding transmission function (i.e., number of modes per width) across pristine graphene of chiralities from Fig. 1 . Individual chiralities are not labeled because all display the same transmission spectrum. The subset of out-of-plane ZA and ZO modes is shown separately. (c) Computed transport across grains from Fig. 1 , revealing that transmission depends on the grain structure. Grain-4 (g-4) and grain-7 (g-7) have similar transmission, grain-10 (g-10) exhibits lower transmission, and LD has the worst transmission.

Image of FIG. 3.
FIG. 3.

(a) Thermal conductance vs. temperature across various defects (GBs and LD) corresponding to Fig. 1 . Calculations are performed using periodic boundary conditions in the transverse direction (width 6.5 nm) based on transmission spectra of Fig. 2 . The upper limit of ballistic conductance in graphene with no defects ( ) is displayed for comparison. (b)Thermal conductance vs. temperature along graphene with a defect, normalized by the ballistic conductance of the same case with no defects ( ). At room temperature, the grain-4 and grain-7 GB structures show the largest thermal conductance (∼80% of pristine graphene), and the LD the lowest (∼50% of pristine graphene).

Image of FIG. 4.
FIG. 4.

Thermal properties of structures calculated without using periodic boundary conditions in the transverse direction. (a) Ballistic thermal conductance in pristine GNRs of the chirality indicated, see Fig. 1 . (b) Phonon transmission in GNRs with a GB or LD normalized by transmission of the same GNRs without defects (T GB) as a function of phonon energy, ℏω. (c)Thermal conductance vs. temperature along GNRs with a defect, normalized by the ballistic conductance of the same GNRs with no defects ( ).

Image of FIG. 5.
FIG. 5.

(a) Simulation results (without GBs, lines) fitted against experimental data (Ref. 31 , symbols) for thermal conductivity of monocrystalline graphene on SiO2 substrate. (b) Corresponding thermal conductivity of polycrystalline graphene as a function of average grain size G, calculated using the thermal conductance of GBs from Fig. 4 . The thermal conductivity depends on defect type (GB or LD) and becomes strongly affected when grain sizes are below dimensions a few times the intrinsic phonon mean free path in substrate-supported graphene (∼100 nm at room temperature) (also see Ref. 3 ).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Effect of grain boundaries on thermal transport in graphene