Mechanical Properties of 2D LiInP2Se6: Implication for Semiconductor Applications

Metal phosphorus trichalcogenides (MPTCs) are emerging 2D semiconductor materials with unique functional properties that set them apart from other 2D systems. Despite the importance of their mechanical properties for improving the semiconductor device's durability and performance, as well as for utilizing strain effects to customize material properties and create new functionality, our current understanding of MPTCs' mechanical behavior is lacking and lags behind our knowledge of their other properties. Here, we use LiInP2Se6 as a model example of MPTCs and report the first experimental measurements of the elastic and plastic (fracture) properties along both in plane and out-of-plane directions by atomic force microscopy and nanoindentation. Being a 2D material that is entirely inorganic, LiInP2Se6 surprisingly exhibits mechanical properties that resemble those of hybrid organic-inorganic materials rather than pure inorganic 2D materials. It has a soft crystal structure with low elastic moduli, a low difference in in-plane vs out-of-plane mechanical properties, and a combination of elastic and plastic characteristics of hybrid organic-inorganic materials. Our work provides the mechanical information critically needed to mitigate and/or harness the strain effects in LiInP2Se6-based semiconductor devices and sheds light on the mechanical behaviors of MPTCs with indispensable insights.