Abstract
Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics. Here we report the anisotropic in-plane thermal conductivity of suspended few-layer black phosphorus measured by micro-Raman spectroscopy. The armchair and zigzag thermal conductivities are ∼20 and ∼40 W m−1 K−1 for black phosphorus films thicker than 15 nm, respectively, and decrease to ∼10 and ∼20 W m−1 K−1 as the film thickness is reduced, exhibiting significant anisotropy. The thermal conductivity anisotropic ratio is found to be ∼2 for thick black phosphorus films and drops to ∼1.5 for the thinnest 9.5-nm-thick film. Theoretical modelling reveals that the observed anisotropy is primarily related to the anisotropic phonon dispersion, whereas the intrinsic phonon scattering rates are found to be similar along the armchair and zigzag directions. Surface scattering in the black phosphorus films is shown to strongly suppress the contribution of long mean-free-path acoustic phonons.
Highlights
Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics
On the contrary, such ‘orthogonal’ electronic and phononic transport of black phosphorus (BP) may not be favourable in typical field-effect transistor and photovoltaic devices, as low thermal conductivity in the channel direction can lead to thermal management issues
We report the anisotropic in-plane thermal conductivity of suspended few-layer BP measured by micro-Raman spectroscopy, which has been used for measuring thermal conductivity of 2D materials such as graphene[30,31], MoS2 and hBN34
Summary
Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics. We report the anisotropic in-plane thermal conductivity of suspended few-layer black phosphorus measured by micro-Raman spectroscopy. Some recent first-principles studies raised interest of BP in thermoelectric applications, claiming that because of the anisotropic lattice structure, the ‘armchair’ direction possesses high electrical conductivity and low lattice thermal conductivity, which is desirable for thermoelectrics[21,25,26,27,28]. On the contrary, such ‘orthogonal’ electronic and phononic transport of BP may not be favourable in typical field-effect transistor and photovoltaic devices, as low thermal conductivity in the channel direction can lead to thermal management issues. The thickness dependence of the thermal conductivity is attributed to the strong surface scattering of acoustic phonons, especially phonons with long mean-free-path (MFP)
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