  We present experimental results and numerical simulations to investigate the
modification of structural-mechanical properties of ion-implanted
single-crystal diamond. A phenomenological model is used to derive an
analytical expression for the variation of mass density and elastic properties
as a function of damage density in the crystal. These relations are applied
together with SRIM Monte Carlo simulations to set up Finite Element simulations
for the determination of internal strains and surface deformation of
MeV-ion-implanted diamond samples. The results are validated through comparison
with high resolution X-ray diffraction and white-light interferometric
profilometry experiments. The former are carried out on 180 keV B implanted
diamond samples, to determine the induced structural variation, in terms of
lattice spacing and disorder, whilst the latter are performed on 1.8 MeV He
implanted diamond samples to measure surface swelling. The effect of thermal
processing on the evolution of the structural-mechanical properties of damaged
diamond is also evaluated by performing the same profilometric measurements
after annealing at 1000 {\deg}C, and modeling the obtained trends with a
suitably modified analytical model. The results allow the development of a
coherent model describing the effects of MeV-ion-induced damage on the
structural-mechanical properties of single-crystal diamond. In particular, we
suggest a more reliable method to determine the so-called diamond
"graphitization threshold" for the considered implantation type.
