Online photoelectron current spectroscopy of metal powder at atmospheric pressure

This paper introduces a new setup to measure the work function of metal powders and bulk materials, called Powder Photoelectron Current Spectroscopy (PPCS) at atmospheric pressure. This setup, which works in different gas compositions under atmospheric pressure and at room temperature, was developed for the online analysis of the oxidation state of metal powders used in the oxygen-free production, where all processes take place in a controlled environment at extremely low oxygen levels. The PPCS method can refer to many advantages, such as being quick, relatively inexpensive compared with UHV systems, and easy to use, also compatible with small amount of powders (≈1 mg). In this work, fundamental issues of the technique were investigated. In particular, for Cu powder with diameters ranging from 4 to 180 μm, it is shown that the size distribution of the particles does not affect the determination of the work function. In addition, an applied electric field for more efficient removal of the photoemitted electrons does hardly influence the measured work function, i.e., Schottky effects remain negligible. In agreement with the literature, a thin oxide layer on the surface of metal particles leads to a shift of the work function by about 0.5 eV. For instance, the work function of pure Cu plate is 4.5 ± 0.07 eV, while an oxide layer exhibits a WF of 5.15 ± 0.105 eV corresponding to Cu2O [Olszok et al., Aerosol Sci. Technol. 58, 54-69 (2024)].