A crystalline film thinner than a human hair lies on a rigid substrate like a carpet nailed to the floor. The substrate prevents the film from freely changing shape when heated: it expands and contracts stiffly, losing sensitivity. In the new work, the film was separated from the substrate by dissolving an intermediate layer in water. The free-standing film, transferred onto silicon, became four times better at converting heat into an electrical signal at room temperature.

At 60°C, sensitivity increased 34-fold. Microscopy revealed that in the free-standing film, thermal vibrations more easily rearrange internal regions with different charge orientations, as if the carpet can now flex freely rather than just ruffle slightly. Such a film detects infrared heat without the bulky cooling required by conventional detectors and can scavenge low-temperature waste heat from electronics.