Unconventional 2D Materials from Liquid Phase Synthesis

Current 2D materials largely derive from van der Waals -layered bulk structures. However, only a limited number of such structures exist under ambient conditions, and in total only a few dozen 2D crystals have been successfully synthesized or exfoliated. In contrast to previous contributions, in this talk I will discuss a so far unexplored scheme for liquid phase synthesis of 2D materials that is based on the use of graphene oxide (GO) bilayers acting as a template material and kinetic barrier. The GO layers in the presented scheme are of fundamental importance as they prevent crystal growth along out-of-plane high-symmetry directions, and thus the formation of bulk crystalline solids.<br/><br/>Among countless 2D materials that have been predicted based on first principle computations [1], the <i>β</i>-phase of CuI, which is only stable at a narrow temperature range of 645-675 K [2,3], is a prime example of a material that would be impossible to isolate in its monolayer form via exfoliation. In our recent contribution we have synthesized this particular material inside a GO envelope and via atomically resolved scanning transmission electron microscopy have subsequently characterized its structure in great detail [4]; these results will be discussed in the talk.<br/><br/>The applicability of our synthesis method, however, is not limited to this singular structure. Quite the contrary, we have already applied the same process to several other transition metal halides, including 2D silver iodide and magnetic nickel iodide crystals. Moreover, generalizing this concept should allow access to further exotic layered structures, which will vastly expand the currently available library of 2D materials and their incorporation in devices, hence facilitating their structure and properties to be studied in room temperature.<br/><br/>1. Mounet <i>et al. </i>Two-dimensional materials from high-throughput computational exfoliation of experimentally known compounds. Nature Nanotechnology 2018, 13, 246–252.<br/><br/>2. Sakuma, Crystal structure of <i>β</i>-CuI. Journal of the Physical Society of Japan 1988, 57, 565–569.<br/><br/>3. Keen, D., Hull, S. Determination of the structure of beta-CuI by high-resolution neutron powder diffraction. Journal of Physics: Condensed Matter 1994, 6, 1637.<br/><br/>4. Mustonen <i>et al</i>. Toward Exotic Layered Materials: 2D Cuprous Iodide. Advanced Materials 2022 e2106922.