Transport mechanisms in nanostructured porous silicon layers for sensor and filter applications

Mechanisms such as diffusion, adsorption, desorption and capillary condensation of gases or fluidics in porous materials play an important role when using these materials for sensing or filtration. Transport processes were investigated in freestanding porous silicon (PS) membranes for liquids and gases. Transport models in nanostructured PS membranes are analyzed considering several types of transport mechanisms for different liquids and gases. As a new analytical approach, transport of liquids (organic and aqueous solutions) and vapors was studied optically in PS optical multilayers. Adsorption in the meso- and microporous materials occurs rather fast (typical adsorption time of 5 s). Natural desorption time at ambient conditions depends on the vapor pressure of the investigated adsorbates and can be reduced using heating or purging. Adsorption and desorption isotherms are measured to investigate interactions between sample surface and adsorbate as a function of surface treatment and to evaluate specific surface area and pore size distribution of porous material.