Laser stimulated photodetachment of electrons from the surface of planar substrates and nanoparticles

Isolated or negatively biased non-conductive substrate surfaces in low-temperature gas discharges are typically charged by highly mobile plasma electrons. In general, the binding energy of surface electrons is approximately equal to the electron affinity of the material surface [1], which is lower than the work function. Continuous flux of ions, metastables, and UV photons induce secondary electron emission, affecting plasma sheath dynamics, ionization balance, and discharge stability. This raises the question of whether electron emission from highly charged surfaces can exceed that from bulk materials. The detachment of surplus surface electrons - particularly the yield and cross-section - has not been extensively studied for planar dielectric substrates, unlike the well-documented photoemission of bulk electrons. To address this gap, we investigate laser-stimulated photodetachment (LSPD) from plasma-charged substrates and nanoparticles. Our findings reveal that LSPD from planar surfaces induces a nonlinear charge decay with successive laser pulses. The photodetachment yield strongly depends on the initial (remaining) surface charge, charge trap density, material type, and laser wavelength [2]. Experimental measurements on common insulating substrates showed LSPD yields and cross-sections that diverged from expectations based on tabulated electron affinities. Furthermore, the findings suggest a possible pathway for precise surface charge control or removal using low-energy laser photons, minimizing surface damage in plasma and e-beam based applications. LSPD from nanoparticles was also studied in an Ar/C₂H₂ dusty plasma for charge diagnostics. The charge per particle was estimated from particle and photodetached electron densities. Notably, Langmuir probe measurements showed prolonged signal decay after LSPD, attributed to residual negative ions that were likely electrostatically trapped or newly formed, even after the C₂H₂ flow had ceased.

1. M. Shneider, Y. Raitses, S. Yatom, J. Phys. D: Appl. Phys. 56, 29LT01, 439501 (2023)

2. Y. Ussenov, M. N. Shneider, S. Yatom, Y. Raitses, Appl. Phys. Lett. 125, 254102 (2024)