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.組成物はバルク部とそのバルク部に一体化した外表面を有する基体材料（Ｍ）を含む。外表面は表面改質層を含む。表面改質層は外表面から少なくとも１ｎｍの深さまで延びる。表面改質層は、Ｍと金属又は金属合金である少なくとも１種類の他の材料（Ｘ）を含む。表面改質層の２５℃における導電率はＭのバルク部の２５℃における導電率の少なくとも±２．５％である。組成物は周波数選択性表面ベースのメタマテリアルを含む物品であり、複数の表面改質部は共振周波数を発生させる複数の周期的表面素子であってもよい。【選択図】図１
