Conduction and trapping of electric charges in an anisotropic material after irradiation with an electron beam: Application to TiO2 single-crystal

The present work deals with the characterization of the mechanisms occurring during the injection of electrons with a 30 keV electron beam in oriented TiO2 single-crystals, by two complementary experimental methods: the scanning electron microscope mirror effect (SEMME) and the induced current measurement (ICM), respectively used for characterizing the trapping and the motion process of electric charges.The use of several set-ups, allows separating the various components of the current induced in the sample-holder during the injection of the electrons. It highlights, in the case of TiO2, a strong surface diffusion of the charges and a significant tertiary current, due to the secondary electrons re-emitted by the walls of the microscope.SEMME characterizations show that monocrystalline rutile traps a significant quantity of electric charges, depending on the sample temperature during the injection of electrons. Electrons are mainly trapped on the crystallographic orientation of the TiO2 single-crystal and on the structural defects, particularly dislocations. One of the most interesting results is the unusual shape of the mirror image. Depending on the crystallographic orientation, the mirrors can be elliptic (injection on the (1 1 0) plane), or circular (injection on the (0 0 1) plane) proving that the anisotropy of the material plays a significant role on the conduction and trapping mechanisms of charges.