Electron photodetachment from plasma-charged substrate surfaces and nanoparticles

The laser-stimulated electron photodetachment (LSPD) has been proposed as a particle charge diagnostics method in nano dusty plasmas. Additionally, the impact of nanoparticle size on photodetachment energy barrier reduction due to grain charging has been predicted [1]. However, the photodetachment yield and cross sections from material surfaces for real gas discharge plasma charging conditions remain unknown. Here, we report on the study of LSPD from both plasma-charged dielectric planar substrates and carbonaceous nanoparticles grown in a plasma medium. Electron photodetachment from planar insulators such as quartz (fused silica), alumina, and h-BN demonstrates that surface charge decay is nonlinear for subsequent laser pulses, and photodetachment yield defined by the initial surface charge density for the same material [2]. The LSPD from dust nanoparticles was carried out utilizing fast Langmuir probe measurements, synchronized with separate laser shot events. The photodetached electron density obtained from the pulsed probe current and specific charge for the nanoparticles was estimated by using the dust particle density measured by the laser light extinction method. Also, the role of the electron detachment from the residual background negative ions due to the defragmentation of C₂H₂ molecules and sputtering of carbonaceous thin film on the cathode has been discussed.