Tunable coloration of diamond films by encapsulation of plasmonic Ag nanoparticles

Chemical vapor deposition (CVD) grown diamond films are widely used as coating materials. While diamond thin films are typically clear or slightly gray in color, we demonstrate that diamond films of different optical properties and exhibiting different colors can be prepared by embedding Ag nanoparticles into the diamond film. Microwave plasma heating of Ag thin films deposited onto H-terminated diamond films grown on transparent fused quartz substrates leads to de-wetting and formation of a high density, two-dimensional array of size controlled Ag nanoparticles. Surprisingly, scanning electron microscopy and transmission electron microscopy show that starting with Ag films < 30 nm diameter, dewetting and subsequent growth of a second diamond layer encapsulates the Ag nanoparticles, forming dense 2-dimensional arrays of diamond-encapsulated Ag nano particles. Under conditions used here, initial Ag films > 30 Qm thickness lead to more polydisperse nanoparticles and the formation of Ag/diamond core/shell structures. By changing the thickness of the deposited Ag layer, the Ag nanoparticle size distribution can be changed, leading to changes in optical properties. Three-dimensional electromagnetic field modeling was performed for SiO2-diamond/Ag/diamond-air structures produced by de wetting of 20 nm thick Ag films show good qualitative agreement with experimental spectra.