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.