TUNGSTEN PHASE-TRANSFORMATION INDUCED BY LOW-FLUENCE AR IRRADIATION IN CU-W MULTILAYERS

Changes occurring in equiatomic Cu-W superlattices, prepared by direct sputtering, after low-fluence 300 keV Ar2+ ion irradiation were investigated by X-ray diffraction. The profiles were measured in theta-2-theta geometry. A shift of satellite superlattice peaks to higher 2-theta angles was observed for ion doses up to 2 X 10(14) ions/cm2. There were no further changes in peak position for higher doses. This effect cannot be interpreted as being caused by an ion mixing process in the copper-tungsten interface regions nor by stress relaxation effects. X-ray diffraction measurements performed on a pure tungsten layer, 1000 angstrom thick and prepared in the same conditions as the superlattices, revealed the presence of the beta-W phase. After 300 keV Ar2+ ion irradiation with low dose (2 x 10(14) ions/cm2), the 110 peak of the alpha-W structure appeared whereas the 210 peak of the beta-W phase disappeared in the X-ray diffraction profile. Thus, during the first stages of irradiation, the transformation from beta to alpha-phase occurred in tungsten sublayers.