  We carried out simulations of crystal truncation rod (CTR) scatterings, i.e.,
one of the surface X-ray diffraction techniques with atomic resolution, from a
monolayer He film adsorbed on graphite. Our simulations reveal that the 00L rod
scatterings from the He monolayer exhibit notable intensity modifications for
those from a graphite surface in the ranges of approximately L = 0.6 - 1.7 and
L = 2.2 - 3.5. The height of the He monolayer from the graphite surface largely
affects the CTR scattering profiles, indicating that CTR scatterings have
enough sensitivities to determine the surface structure of the various phases
in the He layer. In particular, in the incommensurate solid phase, our
preliminary experimental data show the intensity modulations that are expected
from the present simulations.
