Direct evidence of homoepitaxial growth in the electrodeposition of Au observed by ultra-high resolution differential optical microscopy

The combination of our improved laser confocal microscopy with the differential interference microscopy technique (LCM-DIM) is capable of resolving the monatomic steps with heights of ca. 0.25 nm on Au(111) and Pd(111) surfaces and even 0.14 nm on Si(100) in aqueous solutions. LCM-DIM can also follow dynamic movement of monatomic steps in a large area with short acquisition times (2-10 frames/s), indicating that the LCM-DIM is a powerful in-situ method for evaluating various reactions at solid/liquid interfaces with atomic layer resolution. In this paper, we demonstrate the capability of LCM-DIM for the evaluation of the electrodeposition of Au on an Au(111) surface. It is shown that the Au deposition occurs mainly at atomic steps resulting the layer-by-layer growth at potentials near the onset of cathodic currents over the entire area (ca. 100 × 100 μm square). New small islands with a monatomic height were also observed on atomically flat terraces during the deposition. These islands expanded in the lateral direction, resulting the formation of new layers. LCM-DIM provides direct images of dyammic growth modes in the electrochemical deposition of Au with an atomic layer resolution.