The origin of high energy negative ions during deposition of aluminum doped zinc oxide (AZO) films by dc magnetron sputtering of an AZO (Al2O3: 2.0 wt %) target was investigated by in situ analyses using the quadrupole mass spectrometer combined with the electrostatic energy analyzer. High energy negative oxygen (O−) ions which possessed the kinetic energy corresponding to the cathode sheath voltage were detected. The maximum flux of the O− ions was clearly observed at the location opposite to the erosion track area on the target. The flux of the O− ions changed hardly with increasing O2 flow ratio [O2/(Ar+O2)] from 0% to 5%. The kinetic energy of the O− ions decreased with decreasing cathode sheath voltage from 403 to 337 V due to the enhancement of the vertical maximum magnetic field strength at the cathode surface from 0.025 to 0.100 T. The AZO films deposited with the lower O− bombardment energy showed the higher crystallinity and improved the electrical conductivity.

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In-situ analyses on reactive sputtering processes used to deposit photocatalytic TiO2 were carried out using a quadrupole mass spectrometer combined with an energy analyzer. High-energy negative oxygen ions (O-) accelerated by the cathode sheath electric field of several hundred volts and fragments sputtered from the target were analyzed in relation to the oxygen flow ratio and total gas pressure (P tot). With increasing the oxygen flow ratio over 15%, the deposition rate decreased markedly where the target surface was fully oxidized confirmed by in-vacuo X-ray photoelectron spectroscopy analysis on the target surface. High-energy O- ions with a kinetic energy of several hundred eV corresponding quantitatively to the full cathode voltage were distinctly observed. Such high-energy O- species dominant at P tot = 1.0 Pa showed a marked decrease and disappeared at 3.0 Pa. The photocatalytic activity of the anatase TiO2 films deposited at 3.0 Pa was much higher than that of the film deposited at 1.0 Pa, which could be attributed to the presence of many more recombination centers introduced by the bombardment of high-energy O- ions.