[en] Surface reactions between heated aluminum nanoparticles (Al NPs) and thin α-MoO₃ sheets are investigated. Localized photothermal heating on Al NP clusters is provided by a Raman spectrometer laser, while enhanced heating rates and imaging resolution are enabled by the use of a plasmonic grating substrate. Prominent linear reaction zones extending from Al NPs in the 〈001〉 crystal direction are observed on the surface of the host MoO₃ sheets after heating. Raman spectroscopy and x-ray diffraction indicate that α-Al₂O₃ is generated within these extended reacted regions, while AFM and SEM indicate that the topology of the reaction regions are indistinguishable from the MoO₃ host. We hypothesize that these Al₂O₃ zones are formed by surface diffusion and subsequent sub-surface adsorption of heated Al adatoms along the low-energy 〈001〉 MoO₃ direction. Understanding and controlling these reaction mechanisms could lead to enhanced combustion of Al/MoO₃ nanothermite systems. (paper)