  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. But it is only the plasma sheath which has been studied extensively
ever since the beginning of plasma physics. The wall charge received much less
attention. Especially little is known about the in-operando electronic
structure of plasma-facing solids and how it affects the spatio-temporal scales
of the wall charge. The purpose of this perspective is to encourage
investigations of this terra incognito 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.
