HIGH-TEMPERATURE SCANNING-TUNNELING-MICROSCOPY STUDIES OF OXYGEN-INDUCED RECONSTRUCTIONS OF PD(110)

The adsorbate-induced reconstructions of the Pd(110) surface during di ssociative chemisorption of oxygen have been studied at elevated tempe ratures (between 400 and 520 K) by scanning tunnelling microscopy (STM ). For relatively high exposures, a well-ordered c(2 x 4)-O overlayer is observed which consists of a Pd(1 x 2) added-row reconstruction dec orated by oxygen adatoms. At 520 It this surf;lct displays very little mobility, with defects and step edges remaining stationary over long time periods. For low exposures of oxygen, adsorption onto the clean s urface at 430 K leads initially to the formation of ii Pd(I x 3) missi ng-row reconstruction which is again decorated by oxygen atoms. The de coration shows considerable disorder between the Pd rows, while along the rows the structure is relatively well ordered into a zig-zag chain , Structural models are proposed which satisfy both LEED and STM data and concur with coverages derived by other techniques. (C) 1998 Elsevi er Science B.V. All rights reserved.