Sputtering of Spherical SiO2 Samples

Dust grains in the interplanetary environment can be basically found in two locations-floating in the free space or attached to a surface of asteroids, comets, or moons. They are sputtered by the impacts of energetic ions, and this process supplies the interplanetary space with heavy elements. The sputtering yield is generally estimated on the basis of laboratory investigations of planar samples. We use silica micrometer-sized spherical grains as a prototype of a space-borne dust, bombard them by 2-keV Ar ions, and monitor the influences of simultaneous application of the electron beam as well as the electric field at the dust surface on the sputtering yield. We found that the increase in the sputtering yield due to the electron impact is much larger than expected and it can enhance the sputtering yield by a factor of 1.6 in a comparison with the sole ion bombardment. On the other hand, the influence of the electric field is not so strong (if any) and it is masked by electron impacts in our experiment. Sputtering of the grains fixed at a surface by 30-keV Ga ions revealed that the angular profile of the yield is flatter than that frequently used for a description of the sputtering process. Finally, we compare these results with the published sputtering yield values.