Unexpected Piezoresistive Effect, Room-Temperature Ferromagnetism, and Thermal Stability of 2D β-CuI Crystals in Reduced Graphene Oxide Membrane

2D materials are promising nanomaterials for future applications due to their predominant quantum effects and unique properties in optics, electrics, magnetics, and mechanics. However, explorations in unique properties and potential applications of novel 2D materials have been hampered by synthesis and their stability under ambient conditions. Recently, in the graphene, 2D β-CuI is observed experimentally under ambient conditions. Here, it is shown that this 2D β-CuI@graphene possesses unexpected piezoresistive effect and room-temperature ferromagnetism. Moreover, this 2D β-CuI crystal is likely to be stable in a wide range of temperature, that is, below 900 K. Theoretical studies reveal that the unexpected piezoresistive effect is mainly attributable to the convergence of the electrons on Cu and I atoms to the Fermi level with increasing strain. There is a magnetic moment that is ≈0.97 μ_B on the edge of β-CuI nanocrystal created by an iodine vacancy, which is considered the origin of such strong room-temperature ferromagnetism. Clearly, the 2D β-CuI@graphene provides a promising nanomaterial in the nano-sensors with low power consumption pressure and magnetic nano-devices with a size down to atomic scale. The discovery in the present work will evoke various new 2D nanomaterials with novel properties in nanotechnology, biotechnology, sensor materials, and technologies.