Experimental Investigation into the Reactions Between Liquid Gallium and Inorganic Nitrogen Precursors (N2, NH3, and NH4Cl) at 400–500 °C

Liquid gallium (Ga) provides a dynamic reaction interface covered by a self-limiting native oxide layer, yet the reaction behavior of liquid Ga with different inorganic nitrogen sources and the surface-layer evolution remains insufficiently clarified. Herein, we have comparatively investigated interfacial reactions of pure liquid gallium (Ga) with N2, NH3, and NH4Cl under controlled thermal treatments (400, 450, or 500 °C for a 6 h duration), and further examined the reaction with NH4Cl in non-contact versus direct-contact configurations. The resulting surface films were analyzed using a combination of multiple characterization tools after removing residual liquid Ga underneath. Under N2 at 400–500 °C, the surface products obtained were dominated by oxygen-containing gallium species and no distinguishable nitride phase was detected, indicating sluggish kinetics of nitridation in this temperature range. In comparison, NH3 promoted nitrogen incorporation more effectively. Nitrogen-related signals were also detected in the surface products of the NH4Cl experiments in non-contact and direct-contact modes, whereas direct contact resulted in significantly stronger interfacial restructuring and characteristic morphologies, such as spheres and hollow-shell structures. Overall, the extent of nitrogen incorporation and the morphology evolution are jointly governed by nitrogen-source reactivity, temperature, and local contact conditions, with the native oxide layer mediating the competing oxidation and nitridation processes.