These measurements are essential for the assessment of the use of this material as a substrate for Si-based cooling devices (micro-coldplates). De Boor et al. [16] measured the thermal check details conductivity of porous silicon formed on n-type silicon in the temperature range 120 to 450 K using the 3ω method. Gesele et al. [17] used the same method to measure the thermal conductivity of porous silicon from both p and p+-type silicon in the temperature range 35 to 350 K. In a most recent paper by the authors of this paper [18],

the thermal conductivity of mesoporous Si from p-type Si wafers with resistivity in the range 1 to 10 Ω cm, and 63% porosity was measured for temperatures from 20 to 350 K. The above material was nanostructured with randomly distributed pores in a sponge-like morphology. It was found that the temperature dependence of the thermal conductivity of this type of porous Si in the above temperature range is monotonic and does not show any maximum, as in the case of bulk crystalline Si and other crystalline materials. It is more similar to that of different low thermal conductivity amorphous materials, its value being even lower than that of the most known such materials (amorphous Si, silicon oxide, silicon nitride). selleckchem The

thermal conductivity of highly porous Si at cryogenic temperatures is more than four orders of magnitude lower than that of bulk crystalline Si [18]. This is mainly due to its porous nanoscale structure that causes phonon confinement and phonon-wall scattering that blocks thermal transport [19, 20]. In this study, we extend previous measurements of the temperature dependence of porous Si thermal conductivity to the low temperature range 4.2 to 20 K. We found that at these low temperatures, porous Si thermal conductivity Farnesyltransferase is almost stable with temperature, click here showing a plateau-like

behavior. This behavior is common to glasses and disordered materials (i.e., SiO2, vitreous silica, epoxy resin, etc.), but unusual in crystalline systems. The plateau-like behavior of porous Si thermal conductivity in the above temperature range will be discussed by considering the fractal nature of the material and the existence of localized vibrational excitations (fractons) that dominate at these temperatures. At higher temperatures, other mechanisms are dominant and will be discussed. The obtained absolute values of thermal conductivity of the studied nanostructured porous Si are lower than those of many known low-k materials in the whole temperature range 5 to 350 K. This demonstrates the high potential of this material as a substrate for thermal isolation on the Si wafer (micro-hotplate or micro-coldplate for Si-based thermal and cooling devices).