Thermal conductivity of amorphous carbon thin films

Abstract

Thermal conductivities ⌳ of amorphous carbon thin films are measured in the temperatures range 80-400 K using the 3 method. Sample films range from soft a-C:H prepared by remote-plasma deposition (⌳ϭ0.20 W m Ϫ1 K Ϫ1 at room temperature͒ to amorphous diamond with a large fraction of sp 3 bonded carbon deposited from a filtered-arc source (⌳ϭ2.2 W m Ϫ1 K Ϫ1 ). Effective-medium theory provides a phenomenological description of the variation of conductivity with mass density. The thermal conductivities are in good agreement with the minimum thermal conductivity calculated from the measured atomic density and longitudinal speed of sound.

Effect of microstructure on the thermal conductivity of disordered carbon

“…2a. Firstly, the simulations are in good qualitative agreement with the available experimental data [3][4][5][6][7][8][9][10], particularly given the magnitude of the experimental uncertainties. Secondly, the linear dependence on density is close to that measured experimentally by Shamsa et al, [4], with the gradients differing by just 20%.…”

“…As shown by Angadi et al [28] nanometre-sized sp 3 grains lead to small thermal conductivities (around tens of Wm −1 K −1 ), while larger grains lead to an exponentially increasing thermal conductivity which approaches the diamond limit (2000 Wm −1 K −1 ). Combining our present studies of sp 2 ordering with previous works on sp 3 ordering provides a unified picture showing how the thermal conductivity is determined by the microstructure. We find that density plays a minor role, being important only when the structure is fully amorphous.…”

“…Increasing the grain size will lead to even higher thermal conductivities, tending towards the theoretical limit for graphite of circa 4000 Wm −1 K −1 in the basal plane [26]. This variation mimics the behaviour of highly sp 3 carbons which have been extensively studied [4,5,28]. As shown by Angadi et al [28] nanometre-sized sp 3 grains lead to small thermal conductivities (around tens of Wm −1 K −1 ), while larger grains lead to an exponentially increasing thermal conductivity which approaches the diamond limit (2000 Wm −1 K −1 ).…”

“…Ref [3] Ref [4] Ref [5] Ref [6] Ref [7−8] Ref [8] Ref [9] Ref [10] diamonds in Fig. 2) exhibits no such variability, finding little deviation from a straight line fitted through the simulation data points.…”

“…The triangles and circles in Fig. 2a illustrate the broad experimental spread, showing data from eight different authors using either the 3ω [3][4][5] or optical [6][7][8][9][10] methodology. Some of this variability is due to the specifics of sample preparation, prompting Shamsa et al [4] to perform a series of measurements on carbon films deposited in a systematic manner.…”