In-situ Analyses on Reactive Sputtering Processes to Deposit Photocatalytic TiO₂ Films

Abstract

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.

Spatial distribution of electrical properties for Al-doped ZnO films deposited by dc magnetron sputtering using various inert gases

“…All the curves for the average final energy are exponential in total gas pressure. 31 We also calculated the average final energy of the recoiled Ar, Kr, and Xe neutrals, which were much smaller than that of the energetic O − ions at 0.5 Pa. We also find that O − ions undergo about 1.5 collisions at 0.5 Pa, regardless of the gas species ͓Fig.…”

Positive ion speed at the plasma–sheath boundary of a negative ion‐emitting electrode

“…In applications involving surface production of negative ions, such as in negative ion sources and magnetron sputtering discharges, the low‐pressure plasma is favoured in order to reduce the detachment/recombination loss of negative ions inside the plasma/sheath and to enhance the extraction yield. In this scenario, the sheath in front of the emitting electrode can be assumed to be collisionless, that is, ionization/secondary processes are absent inside the sheath.…”

“…The negative ion emission was also observed from a stainless steel surface due to positive ion bombardment . These negative ions are ballistically accelerated across the cathode sheath with kinetic energies that can adversely affect the quality of growing films deposited at the substrate …”

Visible-light active thin-film WO3 photocatalyst with controlled high-rate deposition by low-damage reactive-gas-flow sputtering

“…Generally, the oxide films deposited by conventional DC sputtering contain numerous structural defects generated by high-energy particles during deposition, such as O − bombardment (with several hundreds of eV of energy) on the growing film surface. [36][37][38][39][40][41][42] However, in the case of reactive GFS, sputtered W atoms are transported by the forced Ar stream to the substrate, where they react with O 2 molecules to form WO 3 on the substrate. In this case, there are no high-energy particles available to generate structural defects.…”