The present invention relates to a handheld material analyser comprising an air-tight chamber having an analysis aperture; an electron beam generation system adapted to direct a beam of electrons through the analysis aperture; an Energy-Dispersive X-ray (EDX) spectroscopy system having a detector located in the chamber; the chamber being adapted to operate at internal pressures between atmospheric pressure and a vacuum of the order of 1 Pa; and a gas inlet adapted to receive an inert gas for generating a plasma in the region of the photocathode. In this way, the plasma can clean the photocathode.