Above-bandgap and sub-bandgap photoelectron emission from diamond‑silver nanocomposite thin films

Recent studies have demonstrated that the introduction of silver nanoparticles into semiconducting films increases their electron emission characteristics and their ability to catalyzing chemical reduction reactions. This study investigates the impact of silver nanoparticles on the electron emission characteristics of diamond thin films. Ag nanoparticles were produced by thermal evaporation onto H-terminated surfaces of freshly grown diamond thin films produced by plasma-enhanced chemical vapor deposition and were then encapsulated using another stage of seeding and diamond growth. The energy distribution of the emitted electrons was characterized when illuminated with sub-bandgap light sources at 261 nm (4.75 eV) and 405 nm (3.05 eV) and with above-band light at 21.2 eV. At 261 nm the diamond-Ag-diamond structures increase photoelectron yield by approximately 3× compared with freshly H-terminated diamond, while at 405 nm the yield is increased approximately 200-fold. Our results suggest that the encapsulated Ag nanoparticle likely increase the yield through a combination of effects, including increasing the amount of sp2-hybridized carbon in the near-surface region, charge equilibration at the Ag-diamond interface, and increased scattering in the near-surface region, thereby increasing the effective optical absorption close to the diamond surface.