Abstract
The room temperature deposition of copper onto a Au(111)-(22×√3) reconstructed surface has been investigated using scanning tunnelling microscopy (STM), up to a copper coverage of approximately 0.7 monolayer (ML). At extremely low coverage (∼0.02 ML), preferential adsorption is observed to occur by displacement of gold atoms and incorporation of copper into the top gold layer at alternate herringbone elbows along the ⟨112⟩ directions. Both fcc regions and hcp regions are occupied. With increasing coverage, incorporation of copper continues but copper is also deposited on top of the incorporated copper islands. When full coverage of these islands to monolayer thickness is reached, further deposition leads to preferential growth of those islands located in hcp regions through both the deposition process and migration of copper from other elbows, predominantly those in fcc regions. Eventually, a critical island size is reached above which atomically thick copper islands exhibit a reconstructed surface similar, in essence, to that of the clean gold surface. Models for the initial adsorption mechanism, island formation and the eventual reconstruction of the copper islands are discussed qualitatively in terms of surface strain within the gold and copper surfaces.
Export citation and abstract BibTeX RIS
GENERAL SCIENTIFIC SUMMARY Introduction and background. Ultra-thin adsorbed layers on single crystal metal surfaces can provide structurally interesting systems in which a balance of forces arises from the adsorbate–substrate lattice mismatch, resulting in generally stressed interfacial layers that tend to minimize the excess energy via surface reconstruction. To our knowledge, few ultra-high vacuum (UHV) investigations of the Cu/Au(111) system have been reported. Here, we present a scanning tunnelling microscopy (STM) study of copper deposition on gold (111), we discuss the early nucleation stage and describe the adlayer evolution with increasing coverage.
Main results. Copper initially adsorbs herringbone elbows at specific places within the Au (111) via a place exchange mechanism. With increased coverage, islands initiated in hcp regions preferentially expand, with growth compatible with the Ostwald ripening process, and eventually these islands coalesce and evolve into a partially incorporated double layer. When islands reach a critical size, the new layer reconstructs in a herringbone-like fashion. At step edges, firstly displaced gold atoms condense, expanding the gold terraces; copper condensation is then seen. Overall, copper appears to grow on Au (111) via a Frank Van der Merwe type mechanism; however, the onset of a further copper layer formation is seen before completion of the previous one.
Wider implications. The information derived by our study reveals, in considerable detail, the role of gold reconstruction in directing the very earliest stages of metal cluster growth. This makes the present paper relevant to those interested in metal-on-metal growth, metal/metal interfaces, network formation based on monodispersed, regularly spaced, features and heterogeneous catalysis.