Effect of substrate bias voltage on the properties of magnetron-sputtered gadolinium layers

Thin gadolinium layers, ∼ 4 μm thick, were deposited on (100) silicon substrates by radio-frequency magnetron sputtering under negative substrate bias voltage, V_b, ranging from zero to 450 V. The substrate temperature, resulting from the sputtering process and the bias voltage, ranged from 433 K at zero voltage to 523 K at 450 V. The effect of V_b on the structure of the fabricated layer and its physical and mechanical properties were studied. The Gd layer obtained at V_b = 150 V had a strong preferred (110) orientation and a dense structure with the highest residual stress (- 5.8 GPa) and argon content (∼ 3 at.%), while layers fabricated under zero bias or under V_b = 450 V had a strong preferred (002) orientation and a less dense structure with lower stress (≤ - 2 GPa) and lower argon content (∼ 0.5-1 at.%). Compared with the (002)-orientated layer, the layer with the highly preferred (110) orientation possessed the highest density (7.9 g/cm³), hardness (4.4 GPa) and oxidation resistance. The (110)-oriented layer exhibited a smooth surface, while the layer having (002) orientation displayed a coarse, "orange-peel" type surface.