The diffusion of individual N adatoms on Fe(100) has been studied using scanning tunneling microscopy and ab initio density functional theory (DFT) calculations. The measured diffusion barrier for isolated N adatoms is E(d) = (0.92+/-0.04) eV, with a prefactor of nu(0) = 4.3x10(12) s(-1), which is in quantitative agreement with the DFT calculations. The diffusion is strongly coupled to lattice distortions, and, as a consequence, the presence of other N adatoms introduces an anisotropy in the diffusion. Based on experimentally determined values of the diffusion barriers and adsorbate-adsorbate interactions, the potential energy surface experienced by a N adatom is determined.

The adsorption of CO on Pt(111) has been studied with variable temperature scanning tunnelling microscopy (STM). The well-known c(4×2)–CO structure formed at saturation has been used as a test system for the determination of molecular adsorption sites in an overlayer structure from comparison between theoretical and experimental STM images. By calculating the STM images of the c(4×2)–CO structure with CO placed in different adsorption sites on the surface, only the structure with CO in on-top and bridge sites agrees with the experimental images.

A new concept called configuration distribution analysis is introduced to extract quantitative information on adsorbate-adsorbate interactions from high-resolution scanning tunneling microscopy data. From atom-resolved nitrogen island configurations on an Fe(100) surface we show that the propensity to form small, compact c(2 X 2) nitrogen islands is due to a nearest neighbor repulsion and next-nearest neighbor attraction. We demonstrate the importance of including many-body terms and elastic interactions to account for the detailed description of the island distribution.

The growth and chemical reactivity of Pt on Au(111) have been studied using scanning tunneling microscopy (STM) and temperature programmed desorption (TPD). Deposition of Pt at coverages from 0.02ML up to 2.5ML on Au(111) at room temperature initially leads to the formation of a surface alloy, in which 3% of the Au atoms are replaced by Pt. Subsequent Pt evaporation leads to island growth with a mixed Pt–Au island composition. The reactivity of the Pt/Au system is studied using CO as a probe molecule. We show that a stronger bonding of CO to the first layer of Pt on Au(111) exists compared with the binding of CO on clean Pt. The Au substrate therefore very surprisingly increases the Pt overlayer reactivity. The results can be understood in a simple model, in which the change in the CO binding energy is directly proportional to the shift of the d-band center of the metal overlayer. According to this model, the increased reactivity of the Pt/Au(111) system should hold for other adsorbates and reactions as well.

The growth of cobalt on Cu(111) has been studied using a variable-temperature scanning tunneling microscope (STM). At a deposition temperature of 150 K, one observes the growth of three-layer Co islands with one subsurface layer. The Co islands are surrounded by a brim of Cu. The distinction between Co and Cu is made by adsorption of CO which adsorbs only on Co at room temperature, resulting in a Co(111)-(√3 × √3)R30°-CO structure. After heating the surface, or depositing Co at higher temperatures, the Cu brims gradually disappear, and vacancy islands form in the Cu(111) surface. The top-layer CoCu composition changes slowly at room temperature with Co being replaced by Cu on a timescale of ∼ 1 h, consistent with earlier ion-scattering studies. The experimental findings are in accordance with ab-initio total-energy calculations showing the thermodynamically stable island configuration to be several cobalt layers capped with one copper layer.

By means of scanning tunneling microscopy we have studied the growth of C-60 on the Cu(110) and Ni(110) surfaces. A surprising difference in the C-60 structures formed is observed, despite the fact that the two (110) surfaces geometrically possess a high degree of similarity. On Cu(110) C-60 forms the expected close-packed hexagonal overlayer, whereas C-60 induces a restructuring of the Ni(110) surface. The surprising difference between the Cu and Ni surfaces is tentatively explained within a simple model, based on the interaction between the molecular orbitals of C-60 and the narrow d bands of the surface.

The adsorption of C60 molecules on a Cu(110) surface has been studied by scanning tunneling microscopy. On the clean Cu surface, the C60 molecules nucleate into well-ordered islands with a distorted hexagonal structure which can be written as 100±3 using the matrix notation. The C60 structure is unchanged upon oxygen adsorption, with a (2 × 1)-O structure forming around the C60 islands. Predosing small amounts of oxygen at elevated temperature to create alternating stripes of clean Cu and (2 × 1)-O leads to elongated C60 islands nucleated on the stripes of clean Cu, but with the same internal structure as on the clean surface. However, evaporation of C60 on the fully saturated (2 × 1)-O surface leads to completely different C60 structures, as well as to the formation of small domains of the higher-density c(6 × 2)-O structure on the terraces. This is interpreted in terms of the C60 molecules compressing the (2 × 1)-O structure in a competition with the oxygen atoms for surface area.