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 (Na 2 Nb 4 O 11 ) 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 CaNb 2 O 6 , KNb 3 O 8 , and Na 3 NbO 4 , demonstrating its broad applicability to niobate compounds with diverse compositions and crystal structures.
At a wavelength of 295 nm, photodetectors based on the Na 2 Nb 4 O 11 sheets achieved a responsivity of 6.65 A/W, an external quantum efficiency of 2.79´10 3 % and a specific detectivity of 1.09´10 13 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.
Science Bulletin
Experimental study