Chemical-state specificity in surface structure determination

In the pursuit of an understanding of complex surfaces, the problem of obtaining quantitative structural information about local adsorbate geometry is especially difficult. Conventional diffraction methods rely on long-range order of the adsorbed species, rarely present in complex coadsorption systems. Elementally specific local structural probes can help, but ultimately one also requires chemical-state specificity. This can be achieved in structural methods that involve detection of photoelectrons through the well-known ‘chemical shifts’ in core-level photoelectron binding energies; specific methods of this type are scanned-energy mode photoelectron diffraction (PhD) and normal-incidence X-ray standing waves (NISXW). Recent examples of chemical-shift PhD and NIXSW applications to complex coadsorption systems and to larger molecular adsorbates demonstrate this potential.