Aerosol photoemission as a versatile tool for nanoparticle surface investigations: Evaluation of metal oxide formation and surface properties of multi-component particles.

The presented work discusses an analytical setup that is capable of detecting surface alterations of aerosol nanoparticles. Utilizing the photoelectric effect, Aerosol Photoemission Spectroscopy (APES) is introduced as an online technique that determines the electron work function (eWF) of an aerosol particle material at ambient pressure. Beyond the detailed presentation of the experimental setup, the limitations and possibilities of APES are discussed with regard to metal oxide formation in technical and ultra-clean process gases. Deploying APES as an analytical tool operating at atmospheric pressure, the interaction of oxidizing and reducing gas species becomes observable for various metallic nanoparticles. As shown by APES measurements, even nitrogen with a purity of 7.0 (99.99999%) enables oxide formation when a metallic particle material is processed as an aerosol. Contrary to this, ultra-clean process gases, such as nitrogen with 10−13 ppm residual oxygen, allow the synthesis of oxide-free particles. In addition to the influence of oxygen and hydrogen on mono-metallic particles, this work includes the first results of the surface properties of so called "hetero-aggregates," nanoparticles that consist of two metals. Binary particles, such as CuNi or PtFe, exhibit varying alloying and oxidation behaviors, depending on the process gas used, which can be evaluated based on the development of the eWF during particle formation. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]