Template Approach to Large-Area Non-layered Ga-Group Two-Dimensional Crystals from Printed Skin of Liquid Gallium

Two-dimensional (2D) nanostructures are mainly confined to being obtained from intrinsically layered crystals via an exfoliation approach or epitaxial growth method, thereby greatly limiting the choice of 2D crystals available for high-performance optoelectronic devices. Here, we introduce an efficient PDMS printing strategy to simultaneously realize the controllable preparation and subsequent transfer of a large-area non-layered 2D Ga₂O₃ amorphous layer on the basis of ultrathin oxide skin of liquid Ga. More importantly, a template-confined reaction of the 2D Ga₂O₃ amorphous layer is further proposed to achieve other 2D Ga-group crystals including 2D GaN, GaS, and GaP thin layers. The corresponding crystallization and transformation process under the 2D geometrical space is investigated and demonstrated to be polycrystalline nucleation and growth, which still follows the traditional thermodynamic nucleation rule of critical radius. Furthermore, 2D Ga-group semiconductors could easily stack with themselves or other layered 2D crystals such as MoS₂ to construct diverse van der Waals heterostructures for the fabrication of high-performance and multifunctional electronics. We believe that the unique and simple synthetic strategy proposed in this work will promote the preparation and transfer of diverse non-layered 2D crystals for the discovery of new phenomena and functional nanodevices.