The sensor, which is the size of about 1/1000 of the cross-section of a human hair, could help advance the fields of astronomy, health care, and remote sensing, say the researchers. In recent years researchers have learned that twisting certain materials at specific angles can form what are known as “moiré materials,” which elicit previously undiscovered properties. In this case, the researchers used twisted double bilayer graphene (TDBG) – i,e., two atomic layers of natural stacked carbon atoms given a slight rotational twist – to build their sensing device.
This is critical, say the researchers, because the twist reduces the crystal symmetry, and materials with atomic structures that are less symmetrical – in many cases – promise some intriguing physical properties that aren’t found in those with greater symmetry. With their device, the researchers were able to detect a strong presence of what is known as bulk photovoltaic effect (BPVE) – a process that converts light into electricity, giving a response strongly dependent on the light intensity, polarization and wavelength.
The researchers found that the BPVE in TDBG can further be tuned by external electrical means, which allowed them to create “2D fingerprints” of the photovoltages for each different incident light. By applying a convolutional neural network (CNN) – a type of artificial neural network previously used for image recognition – to decipher these fingerprints, the researchers were able to demonstrate an intelligent photodetector.
Its small size makes it potentially valuable for applications such as deep space exploration, in-situ medical tests, and remote sensing on autonomous vehicles or aircrafts. Moreover, say the researchers, their work reveals a new pathway for the investigation of nonlinear optics based on moiré materials.
“Our work,” say the researchers, “not only reveals the unique role of moiré engineered quantum geometry in tunable nonlinear light–matter interactions but also identifies a pathway for future intelligent sensing technologies in an extremely compact, on-chip manner.”