Abstract

Recently, it has been shown that scanning probe microscopes, particularly the scanning tunneling microscope (STM) and the atomic force microscope (AFM), are ideal methods for analyzing surface chemistry in situ. Both instruments allow for atomic resolution in many different environments, including electrolyte, air, cryogen, and vacuum.

We have built a variable temperature STM, capable of operating at liquid helium temperatures. Initial results show the utility of the instrument in imaging inorganic adsorbates on ordered conductive substrates. Further work will focus on using scanning tunneling spectroscopy (STS) to map out the occupied and unoccupied molecular orbitals of the inorganic adsorbates.

Atomic Force Microscopy studies have focused on monitoring corrosion and deposition processes on copper surfaces. In one study, the AFM was used to examine the anodic dissolution of polycrystalline copper in acid media with and without a corrosion inhibitor. An amorphous overlayer and preferential grain boundary etching were observed. The addition of benzotriazole formed a protective film that inhibited copper dissolution. In situ Atomic Force Microscopy (AFM) images of Cu(100) single crystals in dilute acid solutions reveal that a ($\surd$2 x $\surd$2)R45$\sp\circ$ adlattice is formed on this material. We associate the overlayer with adsorbed O or OH$\sp-,$ in which the oxygen is chemisorbed in alternate 4-fold hollow sites. This adlattice can be stripped electrochemically and also redeposited. Lastly, in situ AFM studies of organic adsorbates, urea and pyrazine, on Cu(100) show ordered overlayers. For urea, a c(2 x 4) structure is observed in a NaClO$\sb4$ solution. In pyrazine/NaClO$\sb4$ solutions, two ordered adlattices are observed, one which is a (2 x 1) structure.