Evaporation Process in Porous Silicon: Cavitation vs Pore Blocking.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Porous silicon (PS) exhibits unique properties due to its high surface area and tunable pore structure.
• Understanding gas sorption and evaporation mechanisms in PS is crucial for its applications in sensors and energy storage.

Purpose of the Study:

• To investigate gas sorption and evaporation mechanisms in native and modified porous silicon.
• To elucidate the role of pore structure, particularly ink-bottle pores, on evaporation dynamics.
• To determine if porous silicon behaves as independent pores or a correlated network.

Main Methods:

• Sorption isotherms for helium and nitrogen were measured across a wide temperature range.
• Volumetric measurements and sensitive optical techniques were employed.
• Porous silicon samples included native and those with reduced pore mouths (ink-bottle shape).

Main Results:

• At high temperatures, homogeneous cavitation dominates evaporation for all samples.
• At low temperatures, evaporation is governed by meniscus recession, influenced by pore length and mouth size.
• Short ink-bottle pores (<1 μm) act independently, while long ink-bottle pores show long-range correlations.
• Evaporation in long ink-bottle pores occurs via collective percolation, not heterogeneous cavitation.

Conclusions:

• Porous silicon is an anisotropic 3D pore network, not merely an array of independent pores.
• Evaporation mechanisms in porous silicon are diverse and depend significantly on pore geometry and temperature.
• The findings challenge previous assumptions about evaporation in ink-bottle shaped pores.