Microstructure of electrodeposited Co-W thin films

Cobalt-tungsten thin films, 300-500 Å thick, containing 0-15 at. % (0-35 wt. %) tungsten have been prepared by electrodeposition onto polycrystalline copper substrates, from acidic and basic baths of various compositions, at 22, 50, and 90 °C. The grain morphology, phase composition, texture, and defect structure were studied by transmission electron microscopy and diffraction. The deposits were either amorphous (or composed of microcrystallites) or crystalline, depending on the plating conditions. The crystalline films consisted of a dispersion of large grains (≫film thickness) within a background of small size grains (≲film thickness). The crystal structure of the latter was hcp, fcc, or mixed. The hexagonal small grains showed a varying degree of [0001] texture. The large grains consisted of alternate hcp and fcc platelets with a definite mutual orientation relationship: (0001)_h∥(001)_c∥ substrate surface with [101̄0]_h∥[110]_c or (0001)_h∥(111) _c∥ substrate surface with [21̄1̄0]_h∥ [110]_c. The grains of both phases contained extensive stacking faults. The microstructure of the films is discussed and a growth mechanism is proposed in order to account, in terms of mutual epitaxy, for the observed orientation relationship between the hcp and fcc structures.