Monitoring the non-equilibrium electronic response of surfaces during plasma exposure*

Plasmas have long been used for the synthesis and modification of materials because of their unique ability to deliver both energetic and chemically active species to surfaces, which enables the engineering of a material’s surface properties without modifying the material’s bulk properties. Yet despite its widespread use, many details of the effect of plasma treatment on a surface, including the energy transfer of the species making up a plasma and their effects on the material’s electronic and vibrational structure, are still missing in literature. For this reason, understanding the energy transfer at the surface of a material upon plasma exposure is vital in optimizing its use in surface treatment.

In this work, we investigate the optical response of metals upon plasma treatment using a tunable-wavelength pulsed laser. Our approach first utilizes a plasma jet to excite the sample; then, laser pulses are used to probe the carrier dynamics of the irradiated region. By using a tunable-wavelength laser as our probe, we selectively monitor the changes in the optical response of different electronic states, giving direct insight into how plasma excitations influence individual states in a material. This study furthers the understanding of how plasma modifies electronic states under non-equilibrium conditions, allowing for a more precise optimization of surface treatments depending on plasma-surface interaction.