K. Heister et al., Odd-even effects at the S-metal interface and in the aromatic matrix of biphenyl-substituted alkanethiol self-assembled monolayers, J PHYS CH B, 105(29), 2001, pp. 6888-6894
Synchrotron-based high-resolution X-ray photoelectron spectroscopy was appl
ied to characterize self-assembled monolayers (SAM) of biphenyl-substituted
alkanethiols CH3(C6H4)(2)(CH2)(n)SH (BPn, n = 1-4) on Au and Ag substrates
. Beyond previously identified odd-even changes in the packing density and
the tilt angle of the biphenyl moieties, the high-resolution spectra reveal
a number of additional odd-even effects upon variation of the number of me
thylene groups in the aliphatic part in the BPn molecule. Their occurrence
and mutual correlation suggests that a BPn SAM represents a strongly correl
ated, highly ordered molecular assembly. In particular, periodical changes
of a shake up feature in the C 1s region are observed, which are related to
the differences in the arrangement of the aromatic matrix. The width and b
inding energy position of the S 2p signals also exhibit odd-even changes. T
he width changes are associated with the occupation of either equivalent or
nonequivalent adsorption sites on the polycrystalline (111) Au and Ag subs
trates. The comparison of the width values with those for conventional alka
nethiols implies that the substrate bonding of alkanethiols on gold cannot
be described by a single adsorption site.