A normal incidence X-ray standing wave (NIXSW) and near-edge X-ray abs
orption fine structure (NEXAFS) study was performed on saturated monol
ayers of 1-octanethiol on Cu(111). NEXAFS around the S K-edge taken in
normal and grazing incidence revealed that the S-C bond was oriented
with respect to the Cu(111) surface to give a calculated orientation o
f the pendant hydrocarbon which was almost normal to the surface, simi
lar to self-assembled alkanethiols on gold surfaces. Modulation in the
S(1s) photoemission with variation in the energy of the X-ray standin
g wave about the (111) and ((1) over bar 11) Bragg energies was modell
ed to yield values of structural parameters: the coherent position, d(
hkl), and coherent fraction, f(hkl), for the adsorbate with respect to
the bulk Cu lattice planes. For the (111) reflection, d(111)=1.19+/-0
.10 Angstrom, f(111)=0.70+/-0.03 but for the ((1) over bar 11) reflect
ion, f((1) over bar 11) was close to zero (f((1) over bar 11)=0.10+/-0
.05) and d((1) over bar 11) was indeterminate. The coherent fraction f
or the Cu substrate was high for both reflections studied (f(111)=0.95
+/-0.03; f(111)=0.92+/-0.02). The structural parameters are rationalis
ed in terms of penetration of the Cu by thiolate sulfur atoms to cause
a surface layer reconstruction. The resultant adsorbate structure is
either incommensurate or else consists of a large-mesh commensurate su
perlattice in which the S atoms exist at a number of different positio
ns with respect to the ((1) over bar 11)planes of the bulk. (C) 1997 E
lsevier Science B.V.