The present invention relates to the methods and devices for controlling a reactive sputtering deposition of a selected material. The proposed device comprises: a vacuum chamber; a means for supplying of an inert and reactive gas into the vacuum chamber; a means adapted for providing a command to the means for supplying of an inert and/or reactive gas into the vacuum chamber; a source adapted for generating plasma and/or creating a flux of sputtered particles of material; a means adapted for holding or placing on it a substrate to be subjected to sputtering of a film of a selected material; an X-ray source adapted to expose a sputtering target by an X-ray beam; an X-ray fluorescence polycapillary confocal probe adapted to be placed inside of the vacuum chamber and comprising an X-ray optic, where the probe is adapted to collect the X-ray fluorescence signals from a part of the sputtering target and direct them to a signal detecting unit; an X-ray energy sensitive detector being optically connected with the polycapillary confocal probe such as to enable the X-ray optic to direct X-ray fluorescence beam towards the detector from the optic's input end facing the surface of the sputtering target; where the X-ray energy sensitive detector being connected at least with the means for processing the detected signals or interpreting the signals received on the state of oxidation of the target.