Sn-based roughness gradients for high-throughput screening

A method is presented for the creation of nanometer-scale roughness gradients that takes advantage of the natural tendency for Sn to cluster into islands when sputter-deposited. The size of these islands is dependent on the mass per unit area of Sn, which has allowed us to create spreads in island size by depositing linear mass gradients of Sn onto smooth substrates. The root-mean-square roughness of the Sn film varies gradually with position and can span the range from 0 nm up to at least 370 nm. The utility of these gradients has been enhanced by coating with Al2O3, which buries the Sn beneath an inert layer and improves subsequent coating with certain metallic films. The properties of a range of materials can now be readily studied as a function of nanometer-scale roughness by deposition onto these gradients.