In situ scanning tunneling microscopy of electrodeposition of mercury on a well-ordered Ir(1 1 1) electrode

Electrodeposition of Hg at a well-ordered Ir(1 1 1) electrode has been examined by linear sweep voltammetry (LSV) and in situ scanning tunneling microscopy (STM) in aqueous 0.1 M HClO4 containing dilute Hg(ClO4)2. The results of LSV revealed multiple peaks, presumably due to underpotential deposition and diffusion-limited bulk deposition. In situ STM unveiled the details of bulk Hg deposition at bare and iodine-modified Ir(1 1 1). The compositions of the Ir(1 1 1) surface could dominate the morphology of the Hg film. An iodine adlayer rendered layer-by-layer deposition of Hg till the sixth layer when 3D island growth prevailed. High-quality STM atomic resolution identified a well-ordered iodine overlayer residing on top of the Hg film, strongly suggesting that the Hg film was crystalline. At a bare Ir(1 1 1), Hg deposition was also layer-by-layer but only to a thickness of three layers. Without the iodine adlayer, the Hg film was, however, seriously pitted and it was not possible to achieve atomic resolution.