Surface properties of spark-ablated metal oxide nanoparticles studied in-flight

Metal oxide nanoparticles are widely used in catalysis, photovoltaics, and gas sensing, where surface structure and oxidation state strongly influence performance. This work investigates how carrier gas composition, combined with in-flight heating, can be used to control the surface properties of metal oxide nanoparticles generated via the gas-phase method, spark ablation. Sn, Zn, and Al nanoparticles were characterized using in-flight X-ray photoelectron spectroscopy (XPS) at the MAX IV synchrotron radiation facility, enabling near real-time measurement of suspended particles under oxidizing (N₂ + O₂), inert (N₂ and Ar), and potentially reducing (N₂ + H₂ and Ar + H₂) gas environments, without introducing potential changes associated with particle deposition and storage. To support the interpretation of the XPS results, the particle size distributions, spark energy and frequency, and compaction behaviour were studied, providing insight into how material properties and generation conditions affect surface chemistry. The XPS results show that for Sn nanoparticles, surface oxidation state can be tuned from SnO2 to SnO and metallic Sn by selecting appropriate carrier gas and in-flight heating temperature. For Zn, the carrier gas primarily determines the surface composition, while heating has only a minor influence on the balance between ZnO, oxygen-deficient ZnOₓ, and metallic Zn on the surface. In contrast, the surface oxide of Al nanoparticles remains largely unaffected by both carrier gas and in-flight heating. These findings demonstrate how careful control of carrier gas and in-flight thermal processing can be used to tailor nanoparticle surface properties, providing a pathway for designing materials optimized for specific applications. • In-flight XPS reveals true nanoparticle surface oxide without deposition artifacts. • Carrier gas composition controls NP surface chemistry during in-flight heating. • Surface tuning of spark-ablated metal oxide NPs depends strongly on the material. • Carrier gas and heating tune Sn and Zn surfaces, while Al remains highly stable. • Size distributions reveal how spark energy and frequency control NP formation.