Fig. 3

Anodic monolayer stripping. Tapping mode AFM images (2 × 2 μm) and XPS Si 2p narrow scans for S-2 samples on Si(111). Cyclic voltammograms are shown as insets to the AFM images. Data for as-prepared samples are in a and d, and data after the short potential step (0.3 V, 1 min) that lead reproducibly to narrow voltammetric waves (ca. 60 mV fwhm) are in b and e. Owing to the kinetic factors, the narrow waves are lost upon more extensive oxidation of the electrodes (c, f). High-energy emissions from silicon oxides (Si⁺−Si⁴⁺) are evident in e and f, and the evolution of the SiO _x :Si 2p peak area ratios appear as labels in the XPS panels. a Small protrusions are observed (222 protrusions µm⁻², which are on average 0.4 nm in height and 5 nm in radius) over the staircase structure of the 〈111〉 surface (R _q of 0.08 ± 0.02 nm (R _tm =0.15 nm) on the terraces and R _q =0.20 ± 0.15 nm (R _tm =0.63 nm) over the whole area). The number of protrusions increases upon the anodic treatment (327 protrusions µm⁻² in b and 945 protrusions µm⁻² in c) and tracks XPS SiO _x emissions. For clarity and comparison purposes all the AFM images are normalized to 1.4 nm. The scale bar is 500 nm