Continuous adsorption in highly ordered porous matrices made by nanolithography.

The exposed surface area of porous materials is usually determined by measuring the mass of adsorbed gas as a function of vapour pressure. Here we report a comprehensive study of adsorption in systems with closed bottom, not interconnected pores exhibiting different degrees of disorder, produced with methods encompassing nanolithography and dry and wet etching. Detailed adsorption studies of these matrices show hysteresis loops, as found always in pores having sizes of tens to hundreds of nanometres. The observed variations in the loop shape are associated with changes in the pore morphology. In regular pores formed by vertical and smooth walls, continuous adsorption is found for the first time in agreement with thermodynamic considerations valid for ideal pores. This suggests that irregularities in the walls and pore openings are the key factors behind the hysteresis phenomenon. Interestingly, pores having rough walls but a pyramidal shape also do not show any hysteresis.