Metal-adatom compound

A special case is when the electrochem-ically active components are attached to the metal or carbon (electrode) surface in the form of mono- or multilayers, for example, oxides, hydroxides, insoluble salts, metalloorganic compounds, transition-metal hexacyanides, clays, zeolites containing polyoxianions or cations, intercalative systems. The submonolayers of adatoms formed by underpotential deposition are neglected, since in this case, the peak potentials are determined by the substrate-adatom interactions (compound formation). From the ideal surface cyclic voltammetric responses, E° can also be calculated as... 

The microstructure and morphology of thick single-phase films have been extensively studied for a wide variety of metals, alloys, and refractory compounds. Structural models have been proposed (12,13). Three zones with different microstructure and surface morphology were described for thick (tens of micrometers) deposits of pure metal. At low temperature (< 0.3 Tm ), where Tm is the melting point (K) of the deposit metal, the surface mobility of the adatoms is reduced, and the deposit was reported to grow as tapered crystallites. The surface is not full density (Zone 1). At higher substrate temperature (0.3-0.45 Tm ), the surface mobility increases. The surface... 

Of major interest for such processes as oxidation and compound formation are results that show several stages of atomic penetration into the substrate lattice. At metal surfaces, this appears to occur mostly with small atoms oxygen, nitrogen, carbon, as well as hydrogen. In some instances, as the coverage is increased, first an overlayer is formed (e.g. O on Ni(100)). Usually, the adatom occupies high-coordination sites such as hollow sites. On less close-packed surfaces, this site puts the adatom nearly coplanar with the surface metal atoms... 

Most nonmetallic adsorbed atoms will not compress into a monolayer overlayer on the closest-packed metal substrates. There appears to be a short-range repulsion that keeps these atoms apart by approximately a van der Waals distance. Attempts to compress the overlayer further by increasing the coverage (which is carried out by exposing the surface to higher pressures of the corresponding gas) result either in no further adsorption or in diffusion of the adatoms into the bulk of the substrate, forming compounds. 

A material in which the organometallic compound has lost all its organic Ugands and is present on the metallic surface as naked adatoms. 

---