A new film could lead to lighter, more portable far-infrared sensing devices.[Credit: Adam Glanzman]
Developed at MIT and detailed in the journal Nature, an ultrathin device for far-infrared sensing registers tiny changes in heat, reads the complete far-infrared spectrum, and needs no active cooling. All of those qualities are packaged in a film just 10 nanometers thick. The device’s compactness supports lightweight, portable formats such as eyeglasses.
Corresponding authors Celesta S. Chang, Yunfeng Shi, Chang-Beom Eom, Jeehwan Kim, and colleagues describe a novel “release-layer-free atomic lift-off (ALO)” technique. They discovered that lead (Pb) within the PMN-PT structure weakens the covalent bonding at the substrate interface by attenuating electron transfer. The Nature paper explains that this phenomenon allows for precise, high-throughput exfoliation of high-quality, single-crystalline membranes down to 10 nm thickness without needing traditional sacrificial layers. These ultrathin, freestanding membranes achieved a record pyroelectric coefficient (1.76 × 10⁻² C m⁻² K⁻¹).
Inside the 10-nm membrane
Performance begins with the material choice. The “PMN-PT pyroelectric membrane” turns tiny temperature shifts into electrical signals, letting it act as a sensitive heat sensor. Because the membrane is only 10 nanometers thick, its thermal mass is low, enabling operation without external refrigeration. Operating at room temperature also trims system power demands and eliminates bulky cryogenic add-ons found in many existing far-infrared systems. The Nature paper reports this single PMN-PT layer covers the full far-infrared spectrum, achieving a record-high pyroelectric coefficient, some two orders of magnitude higher than conventional thin films, without cooling.
Remote epitaxy in action
Creating such a wafer-thin but defect-free film involved using lift-off techniques. While established methods like remote epitaxy (pioneered by researchers including corresponding author Jeehwan Kim at MIT) often use an intermediate graphene layer, the team found this wasn’t necessary for PMN-PT. They discovered they could grow PMN-PT directly on a single-crystalline substrate and peel it off intact without needing an intermediate layer, using their Atomic Lift-Off (ALO) technique. A related press release explains that lead atoms within the PMN-PT structure contribute to this easier separation, allowing for an “easy peel-off of epitaxial films.”
This process leaves the substrate intact and ready for another cycle, “substrate reusable after lift-off,” preserving the substrate. The outcome is an intact, free-standing 10-nanometer membrane that retains its crystalline orientation.
Funding for the project came from the U.S. Air Force Office of Scientific Research.
