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Free keywords:
Self assembled monolayers | Alkanethiolates | X-ray exposure |
E-beam damage | NEXAFS
Abstract:
In a previous communication we presented X-ray photoelectron (XP) spectra of alkanethiolate
monolayers deposited from solution onto Au-substrates. In the S2p XP-spectra two
different sulfur species were detected, and interpreted as evidence for disulfide formation,
in agreement with an earlier report using grazing incidence X-ray diffraction (GIXRD)
[P. Fenter, A. Eberhardt and P. Eisenberger, Science 266 (1994) 1216]. Here we present
new experiments revealing that alkanethiolate monolayers adsorbed on Au exhibit an
unexpectedly high cross section for X-ray induced damage. This observation makes a
reinterpretation of the previous XPS data necessary, which
—
together with new data
— reveals that the second S-species observed in the previous experiments (which was interpreted
to indicate disulfide formation) is due to beam damage. The relevance of this
X-ray induced beam-damage for the interpretation of the GIXRD-data will be discussed.
Data obtained with soft X-ray absorption spectroscopy (NEXAFS) for alkanethiolate
monolayers exposed to low energy electrons in the typical energy range of secondary
electrons (E = 0
—
50 eV) reveal the formation of C=C double bonds and provides evidence
that the X-ray induced damage is caused by the secondary electrons resulting from
the photoemission process.
