Multiscale hybrid materials consisting of semiconducting porous solids and soft semiconducting polymer fillers are expected to show interesting actuating and sensory properties.
We present a two-step process to create silicon/polypyrrole nano-hybrids based on electro-chemical etching of pores into a p-doped silicon single crystal followed by a galvanostatic electro-polymerisation of pyrrole to fill the nanopores. The electro-polymerisation initiates at the silicon pore tip, thereby utilizing the quantum wire effect that significantly reduces the electrical conductivity of the pore walls. We compare I/V curves of the electro-polymerisation within nano-porous silicon with a pore diameter of ~10 nm, within a commercially available n-doped macro-porous silicon with a diameter of ~1 µm and, as a reference, on top of a bulk silicon wafer.
The characteristic temporal evolution of the electrical potential at a reference electrode permits to clearly distinguish in-situ the process steps of i) initiation of the electro-polymerisation, ii) polymer growth, iii) transition stage, and iv) polymerisation at the outer surface. Characterization with SEM and elemental EDX analysis in plane-view and on cross-section fracture surfaces clearly indicate the filling of the pores. We identify the ratio of mean pore-depth and -diameter as well as the current density as crucial parameters for a successful electro-polymerisation inside the nanoporous system.