Single-Nanoparticle Plasmon-Driven Phase Engineering of Two-Dimensional MoTe₂

All-optical control of material phases at the nanoscale enables reconfigurable platforms for sensing and nanophotonics. We present a plasmon-driven strategy to both write and read localized 2H→1T' phase transitions in few-layer MoTe₂ using individual Au nanoparticles as dual-function nanoantennas. Their localized surface plasmon resonances concentrate continuous-wave laser excitation to drive the transition via hot carriers and local heating, reducing the threshold power by nearly an order of magnitude, while their dark-field scattering spectra provide in situ optical readout through characteristic redshift-then-blueshift behavior. Raman spectroscopy confirms formation of the 1T' phase. The Au NP/1T'-MoTe₂ system shows a strong temperature-dependent scattering response, enabling nanoscale optical thermal sensing. In an Au/MoTe₂/MoS₂ vertical heterostructure, plasmon-induced 2H→1T' conversion reconfigures the band alignment, turning a photoluminescence-quenched OFF state into a trion-dominated ON state. This establishes a general route for all-optical, nanoscale phase engineering of 2D materials for active thermal and excitonic control.