In some examples, a method including depositing a functional layer over a substrate; depositing a granular layer over the functional layer, the granular layer including a first material defining a plurality of grains separated by a second material defining grain boundaries of the plurality of grains; removing the second material from the granular layer such that the plurality of grains of the granular layer define a hard mask layer on the functional layer; and removing, via reactive ion etching with a carrier gas, portions of the functional layer not masked by the hard mask layer, wherein the carrier gas comprises a gas with an atomic number less than an atomic number of argon.