PPBD deposition from water nears an early plateau for active functional groups detectable by CV in only 2 minutes, while the deposition from ACN on gold is nearly complete after 5 minutes. (Figure ) In both cases, the surface coverage is similar to values for a monolayer on ITO or gold respectively. Interestingly, after a period of relative stability, coverage continues to increase beyond the highest value reported in literature for a close-packed monolayer on either ITO or gold. We attribute this super-monolayer surface concentration to the presence of a polymer thin film covered in ferrocene groups, with the 3-dimensional roughness of the film allowing a "skyscraper" packing of the groups on the surface. The rms roughness of the film increases from ca. 2 nm with 5 min PPBD deposition time (a roughness indistinguishable from the substrate, and consistent with the presence of a thin uniform film) to 6-8 nm with 60 min PPBD deposition time, yielding a film with an increased surface area. (Figure ) PPBD deposition on ITO surfaces from acetonitrile is much slower, as previously noted. This is a reasonable result in light of the greater stability of PPBD in acetonitrile, but yields the significant implication that ITO does not directly reduce PPBD under these reaction conditions as do metals or conducting carbon. This result is consistent with ITO's well-known use as a hole-injection material with organic compounds, and is reminiscent of other findings of complex interfacial interactions between ITO and organic thin films where ITO's conductivity is found to be due to surface states rather than electrons occupying a high-energy conduction band. Other reports of aryl diazonium grafting on ITO do not mention spontaneous reaction. In films deposited from acetonitrile, the nanoscale structure of the surface eventually becomes smoother than the underlying oxide or gold, (Figures and) consistent with the hypothesis that the surface produced by PPBD deposition is a uniform polyarene thin film similar to that seen in reductivelydriven diazonium film deposition experiments. Interestingly, this film has a higher electrochemical surface coverage at long reaction times. Because of the rigidity of polymers containing phenylene or azobenzene backbone groups, it is unlikely that functional groups contained in the deep interior of the polymer would be accessible for reaction, so we believe that electrochemically measurable ferrocene groups are likely located near the surface of the polymer film. The higher surface coverage may be due to the increase in surface area due to the appearance of the finergrained features. (Figure )