Provided herein is an apparatus including a layer stack. A first granular metal layer overlies the layer stack, wherein the first granular metal layer includes first metal grains separated by voids. A first granular non-metal layer overlies the first granular metal layer, wherein the first granular non-metal layer includes first non-metal grains separated by a first segregant. A second granular non-metal layer overlies the first granular non-metal layer, wherein the second granular non-metal layer includes second non-metal grains separated by a second segregant. A second granular metal layer overlies the second granular non-metal layer, wherein the second granular metal layer includes second metal grains separated by a third segregant.