Optical coherence tomography measurement of capillary filling in porous silicon

Abstract

The use of nanoporous structures with known morphology allows studying the properties of fluids in conditions of strong spatial confinement. Alternatively, the capillary filling of nanoporous structures with simple fluids provides information on their morphology. When a liquid enters the porous structure there is an increase in the optical path of the porous layer, and measuring this optical path as a function of position and time allows evaluating the filling dynamics of the pores. In this work, we determined the capillary filling dynamics of nanostructured porous silicon (PS) by optical coherence tomography. The high spatial resolution of this technique allows one not only to follow the position of the liquid front as a function of time but also to resolve in detail the filling fraction profile of the liquid front inside the PS matrix. Moreover, these profiles contain information about the pore size distribution in the PS structure. Therefore, we show how the determination and analysis of the filling fraction profile along the advancing liquid front can be used as a method to study the pore size distribution inside PS structures.