Atomic adsorbates on metal surfaces

The free molecules of metallic oxides can best be described as having covalent links, possessing dipoles (58). Similarly oxygen atoms adsorbed on metallic surfaces form covalent bonds, sharing two pairs of electrons with the metal (59) or with one specific atom or two atoms of the metal. Their dipoles point with the negative ends away from the metal. We may, to give an example, express the situation of the adsorption of oxygen on silver by... 

TABLE VII. Other Atomic Adsorbates on Metal Surfaces... 

The study of adsorbates on metal surfaces is a particularly fruitful area, which has received much attention. Experimentally, atomic adsorbates are known to yield very different images ranging from bumps [S on Pt(l 11)] to depression [O on Ni(lOO)] depending on the nature of the interaction with the LDOS of the metal surface [58,70,71]. The phenomenon has been analyzed in terms of the impact of the adsorbate on the local density of states at the substrate Fermi level [57,71-75]. Importantly, even... 

Schardt, B.C., Yau. Shneh-Lin, and F. Rinaldi Atomic Resolution Imaging of Adsorbates on Metal Surfaces in Air Iodine Adsorption on Pt(III), Science, 1050... 

Just as a metal may play the role of a halogen atom in the adsorption of alkali ions discussed in the previous section, it may in other cases act similarly to the chlorine atom in HC1 and form a covalent bond. Hydrogen atoms adsorbed on the surface of platinum may serve as an example. The dipoles point with their positive ends away from the metal and may... 

This happens at 8 = 0.134 (827), and at higher 6 values no ions can be formed on the surface. In our earlier considerations (328) we suggested that atoms would be adsorbed next to the ions and be polarized by them. Though we stated there that a sharp distinction between ions and atoms could not be made, we had better consider this old picture obsolete and replace it by the picture of the adsorption of atoms, which are still strongly polarized by the metal surface. Even physically adsorbed atoms are polarized in the same direction when adsorbed on metal surfaces (Secs. V,7 and VI, I). The nature of the adsorption, therefore, changes at higher degrees of occupation. 

Figure 1. Charge transfer Aq/e from the zigzag SWCNTs (p,0) with p = 5-15 to the F atom adsorbed on their surfaces as a function of the tube radius R. The heavy dots and triangles refer to semiconducting and metallic SWCNTs, respectively. The solid lines are intended as a guide to the eye.

Returning to the possibility of quantum delocalization, one could expect that the light H atoms adsorbed on a surface would behave similar to the electrons in free-electron metal surfaces, provided the energy barrier for the H atoms to move across the surface, i.e., the diffusion barrier is very small. This barrier has to... 

Some catalytic reactions proceed only on surfaces with a specific structure. In fine chemistry, the size of metal particles can significantly affect catalytic activity and selectivity. With small metal particles, penetration of foreign atoms into the metal surface can proceed easily, because the number of neighboring metal atoms in the surface is small. As might be expected, the catalytic reactions of foreign atoms penetrating into the metal surface is often different from that of foreign atoms adsorbed on the surface. The most well known example is the activity of... 

The dissociation of oxygen molecules into atoms adsorbed on the surface of a metal or oxide is a particularly simple reaction, which has been investigated with the help of various methods. 

Graham, A.P. The low energy dynamics of adsorbates on metal surfaces investigated with helium atom scattering. Surf. Sci. Rep. 2003, 49,115. 

At higher temperatures, still another effect comes into play vibrational excitation of adsorbed H atoms will cause transfer into delocalized band states. This effect was first predicted theoretically for H atoms adsorbed on Ni surfaces [43,44] and demonstrated by a combination of theory with vibrational spectroscopy for the system H/Pt(l 11) [45,46]. For not extremely low temperatures, the low-lying vibrational excitations will cause the H atoms to become delocalized (like the conduction electrons in a metal), and thus diffusion obtains a different meaning. 

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