AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP7
Photoelectron Spectroscopy Studies of Potassium Deposition on Self-Assembled Monolayers

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: J.E. Whitten, The University of Massachusetts Lowell
Authors: H. Ahn, The University of Massachusetts Lowell
J.E. Whitten, The University of Massachusetts Lowell
Correspondent: Click to Email
The deposition of potassium in ultrahigh vacuum on alkanethiols self-assembled on gold surfaces has been investigated with X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). Several issues have been studied, including extent of penetration of the metal and chemical interaction with the organic layer. In the case of methyl-terminated alkanethiols, it is found that potassium penetrates and interacts weakly with the monolayer, as indicated by minimal changes in the valence electronic spectra, even for large metal doses. Angle-resolved XPS and changes in the areas of the K2p, C1s, S2p, and Au4f peaks with increasing potassium dose confirm penetration. Work function measurements, obtained from the widths of the UPS spectra, are consistent with metal diffusion through the methyl-terminated alkanethiols to the gold interface, and work function changes approaching -2 eV are observed for several atomic layers worth of potassium. These types of studies have been performed for a variety of chain lengths and at cryogenic and room temperature. In general it has been found that potassium-induced C1s core level shifts, using XPS when the spectra are referenced to the Fermi level, are a misleading indicator of chemical interaction and essentially disappear when the peaks are referenced to the vacuum level. On the other hand, the Au4f peaks do not shift with respect to the Fermi level. These data suggest that the C1s alkanethiol orbitals are pinned to the vacuum level, and angle-resolved XPS has been to quantify and study this effect as a function of depth.