Adding structural diversity to roughness gradients formed from Sn

Nanoscale roughness gradients formed from gradients in the mass per unit area of sputtered Sn were previously reported in the literature. In the accompanying report, we identify three approaches that enhance or complement these gradients by allowing more diverse Sn structures to be generated. The first approach is to alter the substrate chemistry, which was explored by sputtering Sn onto the thin-film library Cu1 − xCrx (0 < x < 1) and onto thin films of Co, Ti, V and W. Sn structure was highly sensitive to substrate chemistry, which should provide a means of incorporating morphology as a variable alongside roughness in gradients of nanotopographies. In the second approach, a small amount of Cr is added to a film of Sn to reduce the size of Sn crystallites. By spatially varying the Cr composition, a gradient in crystallite size can be produced. This is another way of making a roughness gradient, which we have demonstrated by preparing the thin-film library Sn1 − xCrx (0 < x < 0.05). In the final approach, gradients in the mass per unit area of Sn were deposited at substrate temperatures of 14, 112 and 191 °C. While a minor increase in crystallite size was noted for increasing substrate temperature to 112 °C, significantly larger crystallites could be produced at 191 °C. This increase in size at 191 °C corresponded to a near doubling in roughness along the gradient, which suggests that elevating substrate temperature could be a viable means of extending the range in roughness attainable with Sn gradients.