Abstract. A nanolithography system based on an electron microscope has been employed to fabricate x-ray masks in amorphous chalcogenide-metal bilayers in a single processing stage. As a result of electron beam induced chemical modification (ECM) silver nanometre dimensional patterns can be fabricated in these bilayers. These patterns exhibit a different x-ray absorption behaviour from the regions unexposed to the electron beam. Two types of x-ray mask have been formed under different electron beam accelerating voltage conditions.