Formation of macro–meso–microporous multilayer structures

In this study, we present a novel electrochemical technique for the fabrication of macro–meso–microporous multilayer structures. Based on systematic investigation of HF/H2O2/ethanol electrolyte system, all three types of pores (smooth macropores, branched mesopores and spongy micropores) can be produced respectively on highly-doped n-type silicon substrate by varying the applied current density, which determines the pore sizes and morphologies. By applying a multi-step current modulation during anodization, a multilayer consisting of three different pore morphologies (macro-, meso-, and micro-pores), as well as several types of multilayer structures with two different pore morphologies, was fabricated on the same silicon substrate using the same electrolyte. A wide range of porosities (30–82%) can be easily achieved with this approach. The current-burst-model is employed to interpret the mechanism concerning such three types of pores formation.

► We present a novel technique for fabrication of macro–meso–microporous multilayers.
► Pore formation with HF/H2O2/ethanol electrolyte on highly-doped n-type Si is studied.
► Macro-, meso-, and micro-pores can be produced on one substrate with one electrolyte.
► Kinds of multilayers with different morphologies and great potential were obtained.
► A wide range of porosities (30–82%) can be achieved.