On the table lies a layered cake of hexagonal boron nitride flakes, a material similar to graphite but made of boron and nitrogen atoms. One flake is carefully transferred onto another, and at the spot where they overlap, after heating in oxygen, bright single light sources are born. Their density increases up to fifteen times compared to ordinary areas, while the quality remains the same.

Previously, such emitters were produced by irradiation, plasma, or local strain. These methods required sophisticated equipment and often yielded defects with noticeable background or instability. Now it is enough to align two flakes under a microscope and heat them in a tube furnace at 1000 °C in a flow of oxygen. The top layer acts as a lid that protects the defects from burning out: oxygen penetrates to a depth of about 192 nanometers, but under the overlap the defects survive better.

The scientists measured the emission spectra, verified that the sources emit photons strictly one at a time, and confirmed that they do not blink or fade over five minutes. In three independent samples, the emitter density in the overlaps exceeded the control by factors of 2.5, 15.8, and 6.3. The saturation brightness reached 12 million counts per second, and the linewidth remained narrow, from 1.24 to 1.78 nanometers.

Such a simple trick paves the way to creating arrays of single light sources for quantum communication and photonic chips. No vacuum, no lithography, no expensive setups are needed, just two flakes, a furnace, and a bit of oxygen. The layered cake, in which the filling of defects is preserved under the top layer, turned out to be not just a metaphor but a working recipe.