image: The graphical abstract illustrates molecular-sieve-assisted confined growth of ultrathin Na2Nb4O11 sheets, their integration into a UV photodetector, and imaging at 255 and 295 nm.
Credit: © Science Bulletin
Ultrathin wide-bandgap oxides are promising for ultraviolet optoelectronics, but many of these materials are non-layered crystals and are difficult to grow as large, uniform sheets. The research team led by Prof. Jun He at Wuhan University has addressed this challenge with a molecular-sieve-assisted confined molten-salt method for producing ultrathin sodium niobate (Na2Nb4O11) single crystals.
During this process, the synergistic interplay between the molecular sieve and the confined molten-salt environment regulates local mass transport, precursor supply, and growth dimensionality, thereby overcoming the intrinsic tendency of non-layered wide-bandgap oxides toward three-dimensional nucleation. This regulation suppresses uncontrolled nucleation and favors anisotropic lateral growth, yielding ultrathin nanosheets with a thickness of approximately 2.66 nm. Moreover, this general growth strategy was successfully extended to other niobates, including CaNb2O6, KNb3O8, and Na3NbO4, demonstrating its broad applicability to niobate compounds with diverse compositions and crystal structures.
At a wavelength of 295 nm, photodetectors based on the Na2Nb4O11 sheets achieved a responsivity of 6.65 A/W, an external quantum efficiency of 2.79´103% and a specific detectivity of 1.09´1013 Jones. The devices recorded rise and fall times of 0.79 and 1.72 ms, respectively, a bandwidth of about 463 Hz, and stable operation over 3,800 cycles.
The team further demonstrated ultraviolet imaging of a patterned target. Images recorded at 295 nm showed clearer contrast than those recorded at 255 nm. Using the different photoresponses at these two wavelengths, the researchers also built a proof-of-concept physical-layer encoding scheme in which wavelength served as an additional information channel.
The study establishes a practical route to ultrathin non-layered oxides and shows how one material platform can integrate ultraviolet sensing, imaging and information encoding.