A semiconductor film one atom thick is like a tightly stretched membrane. Light makes it flash: luminous points (excitons) are born, which quickly fade. Where the membrane is torn or crumpled, the glow flickers and stutters, like a string with a knot sounding off-key.
Scientists applied a method that records brightness fluctuations (by measuring light) and built a map of “off-key notes”—places where the structure is disturbed. These spots coincided with defects previously found by spectral analysis and probe microscopy. Moreover, heating (reduces disorder) “smoothed out” the film, making the flickering more uniform.
The new method is akin to tuning an instrument by ear: instead of painstaking inspection under a microscope, you just need to see the light shivering. In the future, this will help produce perfect films for flexible screens, lasers, and sensors.
An exciton lives only a few trillionths of a second, but manages to probe neighboring atoms and reveal their arrangement by the brightness of its glow.
In Stanisław Lem’s “The Invincible,” clouds of nanomachines responded sensitively to environmental changes — much like excitons react to defects in the crystal lattice.