Article,
Adsorption geometry of hydrogen on Fe(110)
J. Chem. Phys., 83 (4): 1959-1968 (1985)
DOI: 10.1063/1.449334
Abstract
From an analysis of the low-energy electron diffraction (LEED) intensities
we have determined the adsorption geometry of the two ordered H adlayers
formed at T<270 K on Fe (110): a (2�1) and a (3�1) structure, with
ideal coverages of theta= 1/2 and theta= (2)/(3) . Calculations were
performed for different adsorption sites and structural models, taking
the Fe�H bond length and the first Fe�Fe interlayer spacing as variable
parameters. An R factor analysis was used for quantitative comparison
with the experimental data. In both structures the H atoms are adsorbed
on highly coordinated (i.e., quasithreefold) sites: The R factors
of only the superlattice beams (RZanazzi�Jona=0.26, RPendry=0.55
in the (2�1) and RZJ=0.4, RP=0.58 in the (3�1) structure) are significantly
lower than those from models with a long bridge adsorption site (RZJ=0.37,
RP=0.66 and RZJ=0.6, RP=0.74). The on top site and the short bridge
site can clearly be ruled out. For both structures the minima occur
at the same Fe�H interlayer spacing of 0.9�0.1 �, equivalent to an
Fe�H distance of 1.75�0.05 � or rH=0.47�0.05 �. From the R factor
minimum of all beams(RZJ=0.23, RP=0.46) the first Fe�Fe interlayer
spacing is found to be equal to its bulk value, like on the clean
surface. In the (2�1) structure the only possible arrangement of
the Had atoms consists of dense packed rows in 001 direction which
are separated by a row of unoccupied sites, respectively, due to
a delocalization of the H atoms over two neighboring threefold sites,
short-range fluctuations can be envisaged. Their influence upon I/V
curves and relative intensities of different superlattice beams was
analyzed. As a result this effect could be excluded, large domains
are required, in which only one type of threefold sites is occupied.
For the (3�1) structure a model is favored in which the lateral distribution
of the adatoms differs from a previous suggestion. It is shown that
this model is more plausible in view of the H�H interactions. The
higher density of threefold sites also has implications for the discussion
of the 2D phase diagram of H/Fe (110), especially on the requirement
of trio interactions.
Tags
- ,
- adsorption;
- diffraction;surface
- electron
- fe(110)
- hydrogen
- hydrogen;
- iron;
- properties;
- science;
- site;
- sorptive
