Weakening of olivine by hydrogen implantation: Results of nano-indentation tests and some applications to planetary materials

Sticking of the dust grains is a critical step in planet formation. To investigate the solar wind effect on the dust mechanical properties, we conducted hydrogen implantation experiments (using beam energies of 10 keV, 20 keV and 50 keV) on olivine single crystals and determined the elastic modulus and the hardness as a function of depth by nano-indentation tests. The near surface regions of the samples (to ∼600 nm) show a substantial decrease in both hardness (up to ∼85%) and modulus (up to ∼74%), indicating a large degree of mechanical weakening. The depth extent of the weakened region increases with implantation energy while the degree of weakening decreases with implantation energy. TEM (transmission electron microscopy) observations of the samples show that the depth where damaged region occurs increases with the implantation energy used. The results are interpreted based on the physics of ion-solid interaction during implantation. According to our results, we expect that olivine-like dust exposed to solar wind would display a similar mechanical weakening in the surface (∼ 74% reduction in elastic modulus, ∼ 85% reduction in hardness). Mechanical weakening by solar wind implantation would enhance the sticking of the dust in the disk if dust have been effectively exposed to the solar wind. The present results are also applied to interpret observations of some planetary materials.