Electronic interaction of individual slow highly charged ions with TiO2(110)

A TiO2(110) surface was bombarded with slow iodine highly charged ions (HCIs), Iq+, having a wide range of charge states from Ni-like I25+ to He-like I51+. A scanning tunneling microscopic observation revealed that nanometer-sized hillock or crater structures were created by individual HCI impacts and the size of the structures increased with q. In time-of-flight secondary-ion mass spectrometry, a strong q dependence of the secondary-ion yield of O+, Y(O+) was observed; Y(O+) exceeded Y(Ti+) for q similar to 35. We discuss that these secondary effects are the results of the strong coupling of HCIs with electrons in the valence band of the target.