Physically trapped oxygen in sputter-deposited MoO3 films

In the present study, we show that the stoichiometry of sputtered molybdenum oxide films can be changed from oxygen deficient to, more surprisingly, oxygen rich. O/Mo ratios as high as 3.2 were measured, depending on the oxygen partial pressure in the sputtering atmosphere. It is shown that a substantial part of the excess oxygen is physically trapped in the film while the remaining part is chemically bonded in the form of H2O groups. The presence of physically trapped oxygen is demonstrated through a hydration reaction of the film resulting in the controlled detrapping of both excess oxygen and argon. The quantities of released oxygen are electrochemically measured and compared with the elemental composition of the film as determined by means of Rutherford backscattering spectroscopy (Mo, O, and Ar) and elastic recoil detection (H).