The thermal conductivity (TC) of porous silicon (PS) is lower than that of bulk Si by 2-3 orders of magnitude, making it a useful material for thermal insulation in micro electro-mechanical systems (MEMS) for example. PS samples were formed by electrochemical etching of p+ Si wafers in a HF-based electrolyte; porosity varied from 40 to 80% and thickness from 10 to 25 µm. These samples were irradiated at the GANIL accelerator, using 850 MeV ²⁰⁸Pb ions (SME beamline) or 100 MeV ¹³¹Xe ions (IRRSUD beamline). The fluences ranged from 10¹¹ to 10¹³ cm^-2. Raman spectroscopy and electron diffraction both show the appearance of an amorphous phase following irradiation (up to 50% of PS volume) whereas SEM imaging shows no significant damage to the PS structure. This partial amorphisation is ascribed to interaction in the electronic regime and is presented in detail in [1]. Extending this observation of the amorphisation of PS, this work presents the effect of amorphisation on the thermal conductivity of PS. TC measurements were carried out using two methods: Raman spectroscopy and scanning thermal microscopy. Both methods show a significant reduction of TC in the irradiated partially-amorphous samples: a reduction by a factor of up to 2.5 has been measured. Finite element simulations of the heat flux through a partially amorphous Si column were also carried out, and show a TC reduction consistent with experimental results.

[1]   B. Canut, this conference.

Pascal Newby*, INL-Insa de Lyon / CRN2-Université de Sherbrooke, France
Bruno Canut, INL-Insa de Lyon, France
Séverine Gomes, Cethil-Insa de Lyon, France
Konstantinos Termentzidis, Cethil-Insa de Lyon, France
Olivier Marty, INL-UCBL, France
Patrice Chantrenne, Cethil-Insa de Lyon, France
Jean-Marie Bluet, INL-Insa de Lyon, France
Vincent Aimez, CRN2-Université de Sherbrooke, Canada
Luc G. Fréchette, CRN2-Université de Sherbrooke, Canada
Vladimir Lysenko, INL-Insa de Lyon, France

*presenting author