Researchers used a focused electron beam to make single-photon light sources at precise locations in hexagonal boron nitride (hBN). They confirmed true single-photon emission on three separate flakes, with second-order correlation values g(2)(0) = 0.09, 0.12 and 0.16 (numbers reported without background subtraction). By changing the electron exposure time, the team mapped how yield, spectrum, lifetime and photon purity respond to dose and identified an optimal irradiation window for high-purity emitters. They also heated the samples in situ up to 300 °C and found that emission loss with temperature is reversible when the samples are cooled back to room temperature.

The experiment used a scanning electron microscope to irradiate flakes with a 48.2 pA beam at 10 kV and exposure times varied from 20 to 180 seconds. Optical measurements were taken at room temperature with a 532 nm continuous-wave laser (100 µW) and a long-pass filter that blocks wavelengths below 550 nm. A bright emission band seen near 575 nm at room temperature is assigned to the phonon sideband (PSB) of the emitter; the actual narrow electronic transition, called the zero-phonon line (ZPL), lies nearer 548 nm but is strongly broadened at ambient temperature, so the PSB dominates the spectrum.

As the electron dose increased, a separate emission feature near 580 nm grew stronger. That feature matches the known Raman/G-band of graphitic carbon and indicates a gradually formed carbonaceous layer on the irradiated regions. The authors quantify a signal-to-background ratio (SBR) as the emitter signal near 575 nm over the carbon-related emission near 580 nm. At low doses the SBR is high, but it falls sharply at larger doses as carbon-related light increasingly contaminates the spectrum. Atomic force microscopy (AFM) showed nanoscale surface features whose size grows with dose, consistent with material deposition.