RECONSTRUCTION AND DISORDERING ON (110) FCC METAL-SURFACES

Due to the large number of possible defects available to disorder the fee metal (110) 2x1 missing row reconstruction, there is a particularly rich variety of possible disordered phases. The five distinct disordering scenarios that have been predicted for this reconstruction depend on the relative energy cost to generate the different defects that can form on this surface. Recent high resolution LEED measurements on the clean and alkali covered Pd(110) surfaces have explored a few of these phases. For clean Pd(110), a surface consisting of semi-ordered islands has been demonstrated to exist up to 950 K. The periodic island structure can be predicted by a simple model that includes step-step interactions and strain relaxation in the islands. Subsequent alkali adsorption destroys the island structure and forms the 2x1 missing row reconstruction. Diffraction results will be presented as a function of alkali coverage that show that the Pd(110)+K 2x1-->,1x1 transition is an example of deconstruction to the ''even'' flat phase. The existence of this intermediate phase has important implications to the growth of the missing row reconstruction and the range of the alkali-substrate interaction. In addition to these observations, higher potassium coverage data demonstrates that the Pd(110)+K work function minimum is correlated with a surface roughening transition.