Chemisorption, diffusion and reactions on surfaces by scanning tunnelling microscopy

Abstract

We discuss several applications of scanning tunneling microscopy (STM) to studies of chemisorption and surface reactivity. These include : (i) adsorbateadsorbate interactions and diffusion phenomena. We illustrate this with the example of S on Re(0001), where the hopping (diffusion) of S atoms across surface sites was viewed by use of STM. The observed atomic motion was found to be highly correlated, as in a lattice 'liquid'; (ii) interaction between different co-adsorbed species, including S and CO, and benzene and CO, that display both repulsive and attractive interactions leading to the segregation or intermixing of the adsorbates; and (iii) adsorbate-substrate interactions that lead to various surface reconstructions, step restructuring and faceting. We give recent results showing CO and S inducing step restructuring and reconstruction of a Pt(ll1) crystal substrate. Finally, we illustrate the unique capability of STM of operating in virtually any environment by studying the structure of Pt( 110) and Pt( 11 1) surfaces in various gas environments (H, , 0, , CO, propylene) and at pressures of up to 1.6 atm.

CO2 + O on Ag(110): Stoichiometry of Carbonate Formation, Reactivity of Carbonate with CO, and Reconstruction-Stabilized Chemisorption of CO2

“…CO 2 appears to be moving along the added Ag rows. Similar observations have been made for S on Re(0001) where simulated images of diffusing S reproduce the exact line features . The mobility along the [1 1̄ 0] direction makes the transient (3 × 2) order invisible in the LEED pattern; the (1 × 2) order is observed instead.…”

Tuning Metal–Metal Interactions through Reversible Ligand Folding in a Series of Dinuclear Iron Complexes

“…These data are comparable to those reported previously for a folded macrocycle geometry that is static on the NMR time scale. 44 The proposed geometry was confirmed by X-ray crystallography, which revealed an Fe 2 (μ-Cl) core, with ∠Fe−Cl−Fe = 72.34 (8)°and d(Fe−Fe) = 2.710(2) Å (Table 1). The crystal structure further reveals significant reduction of the 3 PDI 2 ligand compared to [Fe 2 Cl 2 ] 2+ .…”

“…The ability to vary the distances and spin interactions between multiple metal sites when binding and functionalizing small molecules is important for the proper functioning of many metalloenzymes − and heterogeneous metallic surfaces. − Recent work in molecular cluster chemistry has led to the development of di- and trinucleating ligand frameworks that allow for control over the distances between metal ions (Figure ). This work has provided a means of evaluating the relationship between M–M bonds and the reaction chemistry that occurs between them.…”

A Self-Organized Two-Dimensional Bimolecular Structure

“…Mate and Somorjai were the first to postulate a vertical dipole−dipole interaction mechanism for the ordering process . Adsorbates with a positive dipole moment relative to the surface form-ordered structures when coadsorbed with CO (having a negative moment), while segregation or disorder occurs when CO is coadsorbed with an adsorbate with a similarly oriented dipole moment . The CO + benzene like systems, however, are not particularly appropriate models for the noncovalent interactions envisaged here because both species undergo significant bonding with the metal substrates studied.…”