111 / 2021-07-19 11:04:38

Effect of surface oxidation on the SiV PL properties in the nanocrystalline diamond films

nanocrystalline diamond,"Chemical vapor deposition (CVD)",surface modification,Optical properties.

Color centers in CVD-deposited nanocrystalline diamond (NCD) particles or films always exhibit a photoluminescent (PL)-quenching behavior. It has confirmed that the oxidation of diamond in air is an efficient approach to improve the PL properties of color centers. Actually, there are other surface modification methods to oxidize diamond films. In this work, three different surface oxidation approaches (air annealing, acid oxidation and oxygen plasma) is employed to explore the PL evolution of silicon vacancy (SiV) centers in the NCD films. All oxidation methods lead to the bonding of oxygen functional groups at diamond surface. However, compared with the as-deposited films, the SiV PL enhancement is about 105-fold in the air-annealed sample while it is about 7-fold and 2-fold in the acid- and plasma- treated samples, respectively. Combination of Raman spectra, HRTEM imaging with cross-sectional oxygen mapping confirms that such different PL behavior originates from the formed different thick oxidation layers. The air oxidation results in a thicker oxidation layer with improved crystallinity than the other two methods. In addition, when the air-annealed films are re-terminated with hydrogen, the SiV PL emission tends to drop remarkably under the same crystallinity. It indicates that hydrogen termination leads to the PL quenching of SiV centers. Therefore, our work reveals that the direct bonding of oxygen to sp³ carbon or the improvement of diamond crystalline quality plays an effective role in the PL enhancement of SiV centers during the oxidation of hydrogen-terminated NCD particles or films.