J. Phys.: Condens. Matter **14** (1 April 2002)
3085-3092
## Geometry of the (2×1) reconstruction of
diamond (111)

S
Walter^{1}, J
Bernhardt^{1}, U
Starke^{1}, K
Heinz^{1}, F
Maier^{2}, J
Ristein^{2} and L
Ley^{2}

^{1} Lehrstuhl für Festkörperphysik, Universität
Erlangen-Nürnberg, Staudtstrasse 7, D-91058 Erlangen, Germany

^{2} Institut für Technische Physik II, Universität
Erlangen-Nürnberg, Staudtstrasse 7, D-91058 Erlangen, Germany
**Abstract.** A quantitative analysis of the
(2×1)
reconstruction of the diamond (111) surface by low-energy electron
diffraction
(LEED) is presented. Spot intensity versus energy data, *I*(*E*),
were collected for normal incidence up to electron energies of 500 eV
and
analysed using the tensor LEED perturbation method. A close fit between
experimental and calculated data (according to a Pendry *R*-factor
*R* = 0.19) confirms the model of pi-bonded chains at the very
surface,
wherein neighbouring chains are at different heights equivalent to a
considerable
surface corrugation (0.68 Å). We find that the chains are
practically
untilted, i.e. the buckling within the chains is negligible (about 0.01
Å). The possible dimerization of the chains is also very small
(relative
bond-length difference *d* = 0.7%), though the respective limits
of
error would allow values up to about 7%. For the subsurface structure
we
find that the surface reconstruction extends rather deep into the
surface
according to the considerable buckling amplitudes within sublayers down
to the fourth bilayer. All structural parameters retrieved, including
the
negligible tilt and dimerization of chains as well as the extension of
the surface reconstruction to deeper layers, are in excellent
quantitative
agreement with the results of *ab initio* calculations, so
controversies
existing up to now in the literature appear to be resolved.