Figure 3. Thermal conductivity measurements of BP using micro-Raman technique.

(a) Illustration of the experimental setup and an optical image of the produced laser focal line. (b) The lengthwise profile and the knife-edge-measured widthwise integrated profile of the laser focal line. The solid lines are Gaussian function and error function curve fits, respectively. (c) The optical absorptivity A, reflectivity R and transmissivity T of the 9.5-nm-thick suspended BP film on armchair- and zigzag-polarized laser incidence. (d) Laser-power-dependent temperature rise (θ_Raman) of the 16.1-nm-thick BP film determined by the micro-Raman spectroscopy along armchair and zigzag transport directions. The dashed lines are linear fits. (e) Extracted armchair and zigzag in-plane thermal conductivities (k_armchair and k_zigzag) of multiple BP films. Dashed lines are results of theoretical modelling. The grey error bars account for the uncertainty of SiN substrate thermal conductivity k_SiN, whereas the blue/red error bars do not. (f) The anisotropic ratio k_zigzag/k_armchair at different BP thicknesses. The ratio at 12-nm thickness is calculated using linearly interpolated armchair thermal conductivity from adjacent thicknesses.