Formation of nanometric polypyrrole films on Au (1 1 1): A STM, SEM and XPS study

Adsorption of pyrrole (Py) and the electrochemical formation of ultrathin polypyrrole (PPy) films from aqueous solutions of 0.1 M Na2SO4 or LiClO4 and Py of low concentrations onto partially atomically flat Au (1 1 1) electrodes were investigated by voltammetry, electrochemical in situ and ex situ scanning tunneling microscopy (STM), high-resolution scanning electron microscopy (HR-SEM), and photoelectron spectrometry (XPS) methods. The voltammetric measurements showed that the adsorption of Py on the surface of Au (1 1 1) is well detectable. In situ STM measurements demonstrated that direct interaction of Py molecules with the electrode is weak, but the co-adsorption process of sulfate and Py molecules improves adhesion of adsorbed Py layer. The formation of ultrathin PPy layers on the electrode surface is not uniform but more island-like. It was shown that the PPy films deposited galvanostatically from diluted Py solutions were essentially overoxidized, contrary to the ones deposited from more concentrated solutions of the monomer, or by using the potentiostatic deposition mode with a limited anodic potential.

► In situ STM study showed that electrochemical formation of PPy films on Au (1 1 1) electrode starts with adsorption of a thin Py sheet following island-like growth of polymer film until it covers the electrode surface continuously.
► Voltammetric measurements showed that during electrochemical deposition of PPy films from a solution consisting of SO42− ions co-adsorption of the ions and Py molecules could happen that improves adhesion of adsorbed Py layer with the electrode in the first stage of the deposition, and helps imaging the film formation stages with in situ STM.
► Prepared from diluted Py solution ultrathin PPy films having low conductivity can be used for preparation of new type biosensors.