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Journal Articles Applied Physics Letters Year : 2024

Multiscale phonon thermal transport in nano-porous silicon

D. Chakraborty
A. Abdullaev
A. Shamatova
A. Azarov
A. Kuznetsov
Y. Wang

Abstract

We performed a comprehensive multi-scale phonon-mediated thermal transport study of nano-porous silicon (np-Si) films with average porosities in the range of φ = 30%–70%. This depth-resolved thermal characterization involves a combination of optical methods, including femtosecond laser-based time-domain thermo-reflectance (TDTR) with MHz modulation rates, opto-thermal micro-Raman spectroscopy, and continuum laser wave-based frequency domain thermo-reflectance (FDTR) with kHz modulation rates probing depths of studied samples over 0.5–1.2, 2–3.2, and 23–34 μm, respectively. We revealed a systematic decrease in thermal conductivity (k) with the rise of φ, i.e., with the lowering of the Si crystalline phase volumetric fraction. These data were used to validate our semi-classical phonon Monte Carlo and finite element mesh simulations of heat conduction, taking into account disordered geometry configurations with various φ and pore size, as well as laser-induced temperature distributions, respectively. At high φ, the decrease in k is additionally influenced by the disordering of the crystal structure, as evidenced by the near-surface sensitive TDTR and Rutherford backscattering spectroscopy measurements. Importantly, the k values measured by FDTR over larger depths inside np-Si were found to be anisotropic and lower than those detected by the near-surface sensitive TDTR and Raman thermal probes. This finding is supported by the cross-sectional scanning electron microscopy image indicating enhanced φ distribution over these micrometer-scale probed depths. Our study opens an avenue for nano-to-micrometer scale thermal depth profiling of porous semiconducting media with inhomogeneous porosity distributions applicable for efficient thermoelectric and thermal management.
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Dates and versions

hal-04630010 , version 1 (01-07-2024)

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B. Kurbanova, D. Chakraborty, A. Abdullaev, A. Shamatova, O. Makukha, et al.. Multiscale phonon thermal transport in nano-porous silicon. Applied Physics Letters, 2024, 124 (25), ⟨10.1063/5.0205455⟩. ⟨hal-04630010⟩
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