| Abstract
| - In situ scanning tunneling microscopy (STM) has been used to examine underpotential deposition (UPD)of Cu at Pt(111) electrodes in the solutions of 0.01 M HCl and 1 mM Cu(ClO4)2. Cyclic voltammetry revealstwo well-defined features at 0.72 and 0.55 V (vs RHE), where a tailing phenomenon is noted for the formerpeak. In situ STM imaging reveals a disorder-to-ordered transition of the adlayer, as the electrochemicalpotential of Pt(111) was stepped from 0.8 to 0.7 V to facilitate the deposition of a sub-monolayer of Cuadatoms. The ordered adlattice can be approximately characterized as (4 × 4), whose irregular intensitymodulation of the STM atomic features indicates its incommensuratity. Toward the end of the first UPDfeature, deposition of Cu continues, resulting in reconstruction of the (4 × 4) adlattice to (√7×√7)R19.1°.The latter structure is then stable toward further negative potential stepping to the end of the second UPDwave. In situ STM imaging turns fuzzy when the electrochemical potential of Pt(111) is made more negativeto the Nernst value. Varying the operation parameters of the STM can result in atomic structures of notonly the upper layer of chloride but also the lower metallic adlayer or the Pt(111) substrate.
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