IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Monday Sessions
       Session SS1-MoA

Paper SS1-MoA6
Closing the Pressure Gap: Photoemission at 5 Torr and the Premelting of Ice

Monday, October 29, 2001, 3:40 pm, Room 120

Session: Innovations in Surface Science
Presenter: D.F. Ogletree, Lawrence Berkeley National Laboratory
Authors: D.F. Ogletree, Lawrence Berkeley National Laboratory
H. Bluhm, Lawrence Berkeley National Lab and Fritz Haber Institute, Germany
F. Requejo, Lawrence Berkeley National Laboratory
C.S. Fadley, Lawrence Berkeley National Lab and University of California at Davis
Z. Hussian, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Fundamental studies of surface processes and reactions at high pressure are outside the reach of many surface science techniques - the so-called "pressure gap". Scanning probe microscopy and non-linear optical probes can be used to study surface topography and vibrational excitations, respectively, but probes of electronic structure and atomic composition are hard to come by. We have recently extended x-ray photoemission spectroscopy to pressures as high as 5 Torr using a synchrotron light source and a differentially pumped electron transfer lens. One of the first applications of this method has been a study of the pre-melting of the ice surface. The new instrument will be described, and the results on ice pre-melting will be presented. Near-edge x-ray adsorption fine structure (NEXAFS) probes the density of unoccupied molecular states. In the case of water, NEXAFS is sensitive to the effects of hydrogen bonding and can therefore distinguish between water vapor, liquid water and ice. Surface sensitivity was obtained by using the O KLL Auger electron yield as a probe of x-ray absorbtion. Electron spectroscopy allowed the Auger yield to be extracted, since total electron yield measurements were complicated by secondary electron cascades in the gas phase. Pre-melting was investigated for ice, in equilibrium with its vapor, between -40 and 0 C (the vapor pressure of ice at the melting point is 4.6 Torr). NEXAFS results showed that a liquid-like film exists at the ice surface above -20 C, reaching a thickness of ~ 2 nm near 0 C. We also found that the presence of hydrocarbon contamination strongly influenced the pre-melting of ice.