Evaporation Process in Porous Silicon: Cavitation vs Pore Blocking

We measured sorption isotherms for helium and nitrogen in wide temperature ranges and for a series of porous silicon samples, both native samples and samples with reduced pore mouth, so that the pores have an ink-bottle shape. Combining volumetric measurements and sensitive optical techniques, we show that, at a high temperature, homogeneous cavitation is the relevant evaporation mechanism for all samples. At a low temperature, the evaporation is controlled by meniscus recession, the detailed mechanism being dependent on the pore length and mouth reduction. Native samples and samples with ink-bottle pores shorter than 1 mu m behave as an array of independent pores. In contrast, samples with long ink-bottle pores exhibit long-range correlations between pores. In this latter case, evaporation takes place by a collective percolation process and not by heterogeneous cavitation as previously proposed. The variety of evaporation mechanisms points to porous silicon being an anisotropic three-dimensional pore network rather than an array of straight independent pores.

Automated summary

The study measured sorption isotherms for helium and nitrogen in a series of porous silicon samples with varying pore structures. At high temperatures, homogeneous cavitation is the relevant evaporation mechanism, while at low temperatures, the evaporation is controlled by meniscus recession. Samples with ink-bottle pores shorter than 1 μm behave as an array of independent pores, while samples with long ink-bottle pores exhibit long-range correlations between pores. This variety of evaporation mechanisms suggests porous silicon is an anisotropic three-dimensional pore network.