![]() ![]() Rather, we rely on the strong thermoreflectance coefficient of Au at visible wavelengths 16, 17 to directly measure the plasma-induced temperature change on the Au surface by means of lock-in detection at the plasma jet repetition frequency, to obtain nanosecond time resolution. 1.įor the operating conditions in this work, there are negligible laser-plasma interactions, and the reflected beam is not affected by any direct interactions. A simplified schematic of our experimental configuration is shown in Supplementary Fig. ![]() The entire system is exposed to the ambient, with room temperature at a constant 20−24☌ and relative humidity of 35−45%. 1) and simultaneously measure the reflectance of a continuous wave laser from the Au surface at the point of contact. In our experiment, we expose a grounded 80-nm gold (Au, 3-nm RMS roughness) film supported by a sapphire substrate to a pulsed, atmospheric plasma jet (Fig. This cooling is then measured through time-resolved, relative temperature changes in the plasma-exposed material with nanosecond resolution. ![]() This cooling is enabled by exposing a surface to a pulsed plasma, which allows the broad range of different energetic processes associated with plasma exposure to be parsed in time. In this work, we experimentally demonstrate the ability of an incident plasma to cool the surface of a material. While certainly of value, none of these approaches provide a direct measure of the response associated with the flux of species at the surface required to separate the localized and transient energy transport mechanisms from the spatially and temporally averaged net power transfer and temperature rise. More recently, in-situ materials characterization techniques have been developed that allow for real-time or quasi-real-time analysis 14, 15. Our current understanding of energy delivery from a plasma to a material surface and its response is guided using a variety of ancillary plasma diagnostics 7, steady-state temperature measurements 8, 9, models 10, 11, and post-treatment ex-situ surface characterization to “re-construct” energy deposition and absorption 6, 12, 13. This can be understood by considering the power balance at the surface 6, While the benefits or detriments of energy delivery are commonly associated with an increase in temperature, the temperature, is in fact, the net result of the difference between energy delivered to and released from the surface. Aside from intentional material modifications, understanding energy delivery at the plasma-surface interface is critical for an array of technologies such as nuclear fusion, where plasma-facing materials must meet complex, yet strict, requirements to avoid degradation from the aforementioned energetic processes 5. Indeed, the energy flux serves to drive the surfaces out of thermal equilibrium with the bulk material, thus enabling local physicochemical processes that can be harnessed to remove (etch) substrate material, deposit different material, or chemically modify the surface. 1)-an attribute that separates them from other approaches to materials processing. Plasmas have long been used for the synthesis 1 and manipulation 2, 3, 4 of materials because of their unique ability to deliver both energy and chemically-active species to the surface of materials (Fig. The results indicate photon-stimulated desorption of adsorbates from the surface is the most likely mechanism responsible for this plasma cooling. To identify potential mechanisms for this ‘plasma cooling,’ we employ time-resolved plasma diagnostics to correlate the photon and charged particle flux with the thermal response of the material. Here, we use time-resolved optical thermometry in-situ to show that the energy flux from a pulsed plasma serves to both heat and transiently cool the material surface. However, to-date, there have been no reports on the direct measurement of the localized, transient thermal response of a material surface exposed to a plasma. This energy flux serves to heat the surface out of thermal equilibrium with bulk material, thus enabling local physicochemical processes that can be harnessed for material manipulation. Plasmas are an indispensable materials engineering tool due to their unique ability to deliver a flux of species and energy to a surface. ![]()
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