Scanning Tunelling Microscopy

1 Direct Atomic Scale Observation of Electrochemically Controlled Spillover/Backspillover 

Since the pioneering work of Rohrer and Binning,77 scanning tunelling microscopy (STM) has been used to image atomic-scale features of electrically conductive surfaces under ultra-high-vacuum but also at atmospheric pressure and in aqueous electrochemical environments. The ability of STM to image chemisorption and surface reconstruction is well 

As expected, the Pt(l 11) surface is covered under ambient conditions by the well-known Pt(lll)-(2x2)-0 adlattice which corresponds to Oq -0.25 where the superscript Pt denotes that the coverage is based on the total surface Pt atoms. The measured interatomic distance of 5.61 A (Fig. 5.49a) is in excellent agreement with literature for the Pt(lll)-(2x2)-0 adlatice. As manifest by the Fourier transform spectmm (Fig. 5.49b) of the surface image of Fig. 5.49a there exists on the surface a second hexagonally ordered adlattice, 

Upon application of positive potential (UWr=0.4V) for 10 min the surface is cleaned from sodium and one obtains the image of Fig. 5.50a which shows only the Pt(lll)-(2x2)-0 adlattice. 

It is worth noting that each Na atom appears to perturb the electron density of the Pt(lll) surface over large ( 12) atomic distances. This can explain nicely the observed long-range promotional effect of Na on Pt surfaces. It is strongly reminiscent of the IR spectroscopic work of Yates and coworkers who showed that a single adsorbed alkali atom can affect the IR spectra of up to 27 coadsorbed CO molecules.80 

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Figure 5.48. Schematic of the experimental setup for using Scanning Tunelling Microscopy (STM) to investigate a Pt(lll) catalyst-electrode surface.78 Reprinted with permission from Elsevier Science.

H.-W. Fink, Monoatomic tips for scanning tuneling microscopy, IBM Journal of Research and Development 30, 460 (1986). 

The starting point of molecular simulation methods is - as in the density functional theory - the well-defined microscopic description of the system studied. This macroscopic (molecular) specification includes (1) the equations of statistical thermodynamics describing the fluid/fluid and solid/fluid interactions, and (2) the molecular model of solid adsorbent. This model should take into account all possible and reliable information on the solids, most of which can be developed from various modern surface science techniques [417]. For instance, some important data on the bulk crystalline structures are given by the X-ray diffraction or neutron diffraction, but the scanning tunelling microscopy is a valuable source of information on the topography of a surface solid. For solving... 

Moffat TP (1999) Scanning tunelling microscopy studies of metal electrodes. In Bard AJ, Rubinstein I (eds) Electroanalytical chemistry, vol 21. Marcel Dekker, New York... 

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