Molybdenum oxide (MoO x ) films have been deposited by atomic layer deposition using bis(tert-butylimido)-bis(dimethylamido)molybdenum and oxygen plasma, within a temperature range of 50–350¿°C. Amorphous film growth was observed between 50 and 200¿°C at a growth per cycle (GPC) around 0.80¿Å. For deposition temperatures of 250¿°C and higher, a transition to polycrystalline growth was observed, accompanied by an increase in GPC up to 1.88¿Å. For all deposition temperatures the O/Mo ratio was found to be just below three, indicating the films were slightly substoichiometric with respect to MoO3 and contained oxygen vacancies. The high purity of the films was demonstrated in the absence of detectable C and N contamination in Rutherford backscattering measurements, and a H content varying between 3 and 11 at. % measured with elastic recoil detection. In addition to the chemical composition, the optical properties are reported as well.