The most fundamental response of a solid to a plasma and vice versa is electric. An electric double layer forms with a solid-bound electron-rich region—the wall charge—and a plasma-bound electron-depleted region—the plasma sheath. However, it is only the plasma sheath that has been studied extensively ever since the beginning of plasma physics. The wall charge received much less attention. Particularly, little is known about the operando electronic structure of plasma-facing solids and how it affects the spatiotemporal scales of the wall charge. The purpose of this Perspective is to encourage investigations of this terra incognita by techniques of modern surface physics. Using our own theoretical explorations of the electron microphysics at plasma–solid interfaces and a proposal for measuring the wall charge by infrared reflectivity to couch the discussion, we hope to put together enough convincing reasons for getting such efforts started. They would open up—at the intersection of plasma and surface physics—a new arena for applied as well as fundamental research. [ABSTRACT FROM AUTHOR]
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