INSITU OBSERVATIONS OF OXYGEN-ADSORPTION ON A CU(100) SUBSTRATE USING ATOMIC FORCE MICROSCOPY

In situ atomic force microscopy (AFM) images of Cu(100) single crystals in dilute acid solutions reveal that a (square-root 2 x square-root 2)R45-degrees adlattice is formed on this material at negative potentials. This adlattice can be removed by sweeping the potential of the Cu(100) surface approximately 0.5 V negative of the open circuit potential. Based on the insensitivity of the (square-root 2 x square-root 2)R45-degrees structure to electrolyte and electrode surface preparation, and our data showing that Cu(111) surfaces in the same acidic solution exhibit only the hexagonal Cu lattice, we associate the overlayer with adsorbed 0 or OH-, in which the oxygen is chemisorbed in alternate 4-fold hollow sites. AFM images of monatomic steps in an electrochemical environment are reported.