Exceptionally pure epitaxial diamond layers have been grown by microwave plasma chemical vapour deposition, which have low boron doping, from 5 × 10 14 to 1 × 10 16 cm −3 , and the compensating n-type impurities are the lowest reported for any semiconducting diamond, <3 × 10 13 cm −3 . The hydrogen impurities that bind with the boron making them electrically inactive can be significantly reduced by baking the diamond to >700 • C for ∼1 s in air. Schottky diodes made on these epitaxial diamond films have breakdown voltages >6 kV, twelve times the highest breakdown voltage reported for any diamond diode and higher than any other semiconductor Schottky diode.

Rabi splitting between the longitudinal plasmon of a gold nano-bipyramid and the A exciton of monolayer MoS 2 is observed at room temperature. The dependence of the Rabi splitting on the physical dimensions of the nano-bipyramid is reported. The impact of bipyramid length, aspect ratio, and tip radius on the coupling strength is investigated. The mode volume of the nanoresonator is significantly reduced because of the sharp tips of the bipyramid, and the Rabi splitting increases with tip sharpness. The results also reveal that greater Rabi splitting is observed for larger bipyramids, contrasting with results previously reported for different nanoresonator shapes. This shows, for the first time, how the magnitude of the splitting has a different response for particular nanoresonators when tuning the size, without increasing the number of excitons coupled into the system. The Rabi splitting, at zero energy detuning between plasmon and A exciton, increases from ∼55 meV with a 70 nm-long bipyramid to ∼80 meV with a 100 nm-long bipyramid. The increase in coupling strength with size arises because of increasing confinement of the field enhancement at the bipyramid tip.

Epitaxial diamond with remarkably low p-type doping (1×1014–1×1017 cm−3) and exceptionally low compensation ∼1×1013 cm−3, has enabled the demonstration of a optically-switched conduction modulation of the epitaxial layer. Charge exchange between the diamond substrate and the epitaxial layer makes it possible to modulate the conductivity of the epitaxial layer. Incandescent light will make the lightly p-doped epitaxial layer insulating and ultraviolet radiation will make the layer conductive again. Once the layer conductivity has been established it will remain in the same electrical state for days, if kept in the dark.