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Incorporating two-dimensional (2D) diamond nanosheets with fluorescent color centers exhibits great potential in the application of quantum sensing. However, color centers always show poor optical emission in chemical-vapor-deposited (CVD) diamond nanomaterials. To address this issue, Si doped diamond/graphite hybrid films were successfully fabricated in microwave-plasma CVD device. The films consist of diamond-core/graphite-shell nanosheets with high amount of diamond nanocrystalline particles. Two post treatments of acid oxidation and annealing in air were used to tailor photoluminescence (PL) of silicon-vacancy (SiV) centers. The SiV centers in the oxidized samples exhibit small PL increase compared with the as-deposited samples with SiV PL quenching. It is found that the graphite phase is selectively etched away with the presence of nanocrystalline diamond particles during the treatment of acid oxidation while the nanocrystalline diamond particles are efficiently removed with the presence of graphite using the air annealing method. Based on this result, a two-step approach of acid oxidation followed by air annealing was conducted to etch the non-diamond phase, forming diamond nanosheets. The SiV centers exhibit significant PL enhancement with a maximum value of 28 folds, compared with the single-step oxidized samples. The Raman and XPS results reveal that such PL increase originates from direct bonding of oxygen on the carbon. Therefore, our work provides a feasible approach to prepare 2D diamond nanosheets with high-brightness color centers.

Investigation of germanium gate hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with Al2O3 dielectric layer has been successfully performed. The device demonstrates a normally-on characteristics, whose maximum drain-source current density, threshold voltage, maximum transconductance, on/off ratio, subthreshold swing, capacitance, carrier density, saturation carrier mobility, fixed charge density and interface state density are of −37.3 mA/mm, 0.22 V, 6.42 mS/mm, 108, 134 mV/dec, 0.33 μF/cm2, 9.83 × 1012 cm−2, 97.9 cm2/V·s, 7.63 × 1012 cm−2 and 2.56 × 1012 cm−2·eV−1, respectively. This work is significant to the development of H-terminated diamond FET.

Microorganisms promoted corrosion has caused significant loss to marine engineering and the antibacterial coatings have served as a solution that has gained attention. In this study, the chemical vapour deposition technique has been employed to grow three different types of diamond coatings, namely, ultrananocrystalline diamond (UNCD), nanocrystalline diamond (NCD), and microcrystalline diamond (MCD) coatings. The evolution of associated surface morphology and the surface functional groups of the grown coatings have demonstrated antibacterial activity in seawater environments. It is found that different ratio of sp3/sp2 carbon bonds on the diamond coatings influences their surface property (hydrophobic/hydrophilic), which changes the anti-adhesion behaviour of diamond coatings against bacteria. This plays a critical role in determining the antibacterial property of the developed coatings. The results show that the diamond coatings arising from the deposition process kill the bacteria via a combination of the mechanical effects and the functional groups on the surface of UNCD, NCD, and MCD coatings, respectively. These antibacterial coatings are effective to both Gram-negative bacteria (E. coli) and Gram-positive bacteria (B. subtilis) for 1–6 h of incubation time. When the contact duration is prolonged to 6 h or over, the MCD coatings begin to reduce the bacteria colonies drastically and enhance the bacteriostatic rate for both E. coli and B. subtilis.