Nitrogen-Doped Chemical Vapour Deposited Diamond: a New Material for Room-Temperature Solid State Maser

Electron spin resonance (ESR) in polycrystalline diamond films grown by dc arc-jet and microwave plasma chemical vapour deposition is studied. The films with nitrogen impurity concentration up to 8×10¹⁸cm^-3 are also characterized by Raman, cathodoluminescence and optical absorption spectra. The ESR signal from P1 centre with g-factor of 2.0024 (nitrogen impurity atom ccupying C site in diamond lattice) is found to exhibit an inversion with increasing the microwave power in an H₁₀₂ resonator. The spin inversion effect could be of interest for further consideration of N-doped diamonds as a
medium for masers operated at room temperature.