Enhancing\nthe Pressure-Sensitive Electrical Conductance\nof Self-Assembled Monolayers

The inherent large\nHOMO–LUMO gap of alkyl thiol (CnS) self-assembled\nmonolayers (SAMs) has limited their application in molecular electronics.\nThis work demonstrates significant enhancement of mechano-electrical\nsensitivity in CnS SAMs by external compression, achieving a gauge\nfactor (GF) of approximately 10 for C10S SAMs. This GF surpasses values\nreported for conjugated wires and DNA strands, highlighting the potential\nof CnS SAMs in mechanosensitive devices. Conductive atomic force microscopy\n(cAFM) investigations reveal a strong dependence of GF on the alkyl\nchain length in probe/CnS/Au junctions. This dependence arises from\nthe combined influence of molecular tilting and probe penetration,\nfacilitated by the low Young’s modulus of alkyl chains. Theoretical\nsimulations corroborate these findings, demonstrating a shift in the\nelectrode Fermi level toward the molecular resonance region with increasing\nchain length and compression. Introducing a rigid graphene interlayer\nprevents probe penetration, resulting in a GF that is largely independent\nof the alkyl chain length. This highlights the critical role of probe\npenetration in maximizing mechano-electrical sensitivity. These findings\npave the way for incorporating CnS SAMs into mechanosensitive and\nmechanocontrollable molecular electronic devices, including touch-sensitive\nelectronic skin and advanced sensor technologies. This work demonstrates\nthe potential of tailoring mechanical and electrical properties of\nSAMs through molecular engineering and interface modifications for\noptimized performance in specific applications.