A composition of matter includes a substrate material (M) having a bulk portion and an outer surface integrated to the bulk portion. The outer surface includes a modified surface layer. The modified surface layer extends to a depth from the outer surface of at least 1 nm. The modified surface layer includes M and at least one other material (X) which is a metal or metal alloy. The modified surface layer has a 25° C. electrical conductivity which is at least 2.5% above or below a 25° C. electrical conductivity in the bulk portion of M. The composition of matter can be an article that includes a frequency selective surface-based metamaterial, and the plurality of modified surface portions can be a plurality of periodic surface elements that provide a resonant frequency.
