Photoelectrochemical etching of silicon derivatized with an electroactive thiophene-terminated alkyl monolayer: toward a redox center-induced etching activation and anisotropy

The photoelectrochemical oxidation of n-Si(1 1 1)-C₁₀H₂₀COOC₂H₅ (1) and n-Si(1 1 1)-C₁₀H₂₀C(2-thienyl)₂OH (2) in CH₃CN + 10^?1 M Bu₄NPF₆ lead to the formation of macropores resulting from the dissolution of underlying silicon. The cyclic voltammetry study indicates that this etching phenomenon is electrocatalyzed by the oxidation product of terminal di(2-thienyl)carbinol moieties present in 2. Further AFM analysis demonstrates that the etching of silicon derivatized with the electroactive monolayer is of an anisotropic nature because characteristic morphological features are produced. In contrast, randomly distributed macropores without specific geometrical shapes are photoelectrogenerated from 1.