On the mechanism ruling the morphology of silicon nanowires obtained by one-pot metal-assisted chemical etching.

One-pot Ag-assisted chemical etching (SACE) of silicon provides an effective, simple way to obtain Si nanowires (NWs) of potential interest for technological applications ranging from photovoltaics to thermoelectricity. The detailed mechanism ruling the process has not been yet fully elucidated, however. In this paper we report the results of an extended analysis of the interplay among doping level and type of silicon, nanowire nanomorphology and the parameters controlling the chemistry of the etching process. We provide evidence that the SACE mechanism entirely occurs at the interface between the etching solution and the Si substrate as a result of Si extrusion by sinking self-propelled Ag particles. Also, a rationale is advanced to explain the reported formation of (partially) porous NWs at high doping levels in both p- and n-type Si. A model not relying on the asserted formation of potential barriers enables to recover full consistency between SACE electrochemistry and the mechanism of formation of porous silicon in electrochemical cells.

Simple approach for the fabrication of PEDOT-coated Si nanowires.

The synthesis of a conformal poly(3,4-ethylenedioxythiophene) (PEDOT) layer on Si nanowires was demonstrated using a pulsed electrodeposition technique. N-type Si nanowire (SiNWs) arrays were synthesized using an electroless metal-assisted chemical etching technique. The dependence of the SiNW reflection on the concentration of the AgNO3 solution was identified. A reflection of less than 2% over the entire visible spectral range was obtained for these structures, evidencing their excellent antireflective properties. The etched SiNWs nanostructures can be further modified by using a tapering technique, which further preserves the strong light trapping effect. P-type PEDOT was grown on these SiNWs using electrochemical methods. Since the polymerization reaction is a very fast process with regards to monomer diffusion along the SiNW, the conformal deposition by classical, fixed potential deposition was not favored. Instead, the core-shell heterojunction structure was finally achieved by a pulsed deposition method. An extremely large shunt resistance was exhibited and determined to be related to the diffusion conditions occurring during polymerization.