Substrate Van der Waals Force Effect on The Stability of Violet Phosphorous

The weak van der Waals (vdWs) forces between monolayers has been a unique distinguishing feature of exfoliable materials since the first isolation of graphene. However, the vdWs interaction of exfoliable materials with the substrate and how this interface force influences the interaction of vdWs materials with the surroundings have yet to be well understood. Here, we experimentally and theoretically unravel the role of vdWs forces between the recently rediscovered wide band gap p-type vdW semiconductor violet phosphorus (VP), with various substrates (including, SiO₂, mica, Si, Au) and quantify how VP stability in air and its interaction with its surroundings is influenced by the interface force. Using a combination of infrared nanoimaging and theoretical modelling we find three main factors that influence how VP interacts with its surroundings: the vdWs force at the interface, the hydrophobicity of the substrate, and substrate surface roughness. We found that VP can maintain its stability for a prolonged period if it is exfoliated on SiO₂ substrate, followed by mica and Au substrates, and is least stable when placed on a Si substrate. Our results could guide in the selection of substrates when vdW materials are prepared and more generally highlight the key role of interface force effects that could significantly alter physical properties of vdWs materials. Our findings can assist in the choice of substrates to exfoliate vdWs materials and emphasize the crucial impact that interface forces can have on altering the physical properties of exfoliable materials.