LOCAL-STRUCTURE AND PHASE-TRANSITIONS WITHIN ORDERED ELECTROCHEMICAL,ADLAYERS - SOME NEW INSIGHTS FROM IN-SITU SCANNING-TUNNELING-MICROSCOPY

The application of in situ atomic-resolution scanning tunneling micros copy (STM) to the elucidation of local structure and potential-induced phase transitions within:ordered adlayers on monocrystalline metal el ectrodes is discussed, and illustrated primarily for compressed CO adl ayers on Pt(111). The value of the additional structural information o n adsorbate binding sites: that can be obtained from infrared reflecti on-absorption spectroscopy(IRAS) as well as from potentiodynamic STM i maging tactics is emphasized. The atomic-level and nanoscale structura l alterations wrought upon the Pt(111)/CO adlayer by bismuth predosing are described as a further illustration of the synergetic value of th e spatial and surface-bonding information-provided by STM and IRAS. A comparison is made between the potential-dependent adlayer characteris tics of the compressed CO adlayers with iodide adlayers on gold and pl atinum low-index electrodes. Possible reasons for the marked differenc es in the phase-transition behavior of these nonmetallic adlayers are briefly discussed, along with comparisons with analogous adlayers in u ltrahigh vacuum environments.