Figure 4

Schematic diagram of the TOF measurement system for desorbed ions. A positron beam was transported by an axial magnetic field (0.01 T) and was incident normal to the sample surface. The TiO₂ sample was biased at a voltage of 300 V. Annihilation γ rays emitted from the target were detected by a NaI(Tl) scintillator coupled with a photomultiplier tube. The positive ions desorbed from the target were accelerated by the target bias of 300 V and were directed to an ion deflector with a potential difference of 460 V. The ionic trajectories in the deflector were deflected and directed to a MCP ion detector. The e⁺SD-TOF spectrum was obtained through analysis of the time interval between the signals from the NaI(Tl) scintillator and the MCP. An electron gun was mounted on a linear manipulator to move it into and out of the beam path, allowing measurement of the ESD-TOF spectrum.