Surface structure atomic, gold

Iodine and bromine adsorb onto Au(l 11) from sodium iodide or sodium bromide solutions under an applied surface potential with the surface structure formed being dependent on the applied potential [166]. The iodine adsorbate can also affect gold step edge mobility and diffusion of the Au surface. Upon deposition of a layer of disordered surface iodine atoms, the movement of gold atoms (assisted by the 2-dimensional iodine gas on the terrace) from step edges out onto terraces occurs. However, this diffusion occurs only at the step edge when an ordered adlayer is formed [167]. 

The three cases discussed here are the simplest and most important surface structures. Other surface planes, such as (210) or (311), have a lower density of surface atoms and tend to be less stable. In a few cases, notably gold, even these simple surfaces are not stable but reconstruct, forming denser surface structures with a lower surface energy. Adsorption of a species usually lifts this reconstruction, i.e. the original simple surface structure is restored [2], We will discuss an example in Chapter 15. 

Fig. 22. ETEM at 180°C in N2, illustrating the stability of gold nanorods, for nanoelectronics and catalysis applications. Gold atomic layers and surface atomic structures are visible. Surface of gold nanorod at room temperature showing twin defect lamellae on the atomic scale. They indicate interaction of the surfactant with the (110) surface forming twins to accommodate the shape misfit between the two.

Fig. 3. Two STM images of the nickelfl 1 1) surface with 2% (right) and 7% (left) gold coverage, respectively. Au is imaged as dark depressions in the surface. The nickel atoms surrounding the gold appear brighter owing to a local modification of the electronic structure, indicating a changed chemical reactivity of these. Adapted from Reference (79).

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