Characterization and modeling of the temperature-dependent thermal conductivity in sintered porous silicon-aluminum nanomaterials

Abstract

Nanostructured silicon and silicon-aluminum compounds are synthesized by a novel synthesis strategy based on spark plasma sintering (SPS) of silicon nanopowder, mesoporous silicon (pSi), and aluminum nanopowder. The interplay of metal-assisted crystallization and inherent porosity is exploited to largely suppress thermal conductivity. Morphology and temperature-dependent thermal conductivity studies allow us to elucidate the impact of porosity and nanostructure on the macroscopic heat transport. Analytic electron microscopy along with quantitative image analysis is applied to characterize the sample morphology in terms of domain size and interpore distance distributions. We demonstrate that nanostructured domains and high porosity can be maintained in densified mesoporous silicon samples. In contrast, strong grain growth is observed for sintered nanopowders under similar sintering conditions. We observe that aluminum agglomerations induce local grain growth, while aluminum diffusion is observed in porous silicon and dispersed nanoparticles. A detailed analysis of the measured thermal conductivity between 300 and 773 K allows us to distinguish the effect of reduced thermal conductivity caused by porosity from the reduction induced by phonon scattering at nanosized domains. With a modified Landauer/Lundstrom approach the relative thermal conductivity and the scattering length are extracted. The relative thermal conductivity confirms the applicability of Kirkpatrick’s effective medium theory. The extracted scattering lengths are in excellent agreement with the harmonic mean of log-normal distributed domain sizes and the interpore distances combined by Matthiessen’s rule.

Crystallize It before It Diffuses: Kinetic Stabilization of Thin-Film Phosphorus-Rich Semiconductor CuP2

“…On the basis of these results, we assume that the phonon mean free path in the CuP 2– y film is low due to disorder and/or phonon boundary scattering . The latter is likely enhanced by the small grains, low thickness, and porous morphology of the film. − The electronic contribution to the thermal conductivity is negligible due to the low hole concentration of CuP 2– y (Figure ). The thermal conductivities of Cu 3– z P and Cu 1.61 P are only slightly higher and their temperature dependences are similar to the case of CuP 2– y .…”

Crystallize it before it diffuses: Kinetic stabilization of thin-film phosphorus-rich semiconductor CuP2

“…41 The latter is likely enhanced by the small grains, low thickness, and porous morphology of the film. [40][41][42] The electronic contribution to the thermal conductivity is negligible due to the low hole concentration of CuP 2−y (Fig. 8).…”