Secondary Electron Yield of Glassy Carbon Dust Grains

Secondary electron emission from a micron spherical dust grain has been investigated locally by a narrow (less than 30 nm) electron beam at energies ranging from 0.6 to 10 keV using the secondary electron microscopy. For investigations, glassy carbon grains were chosen for their conductivity and smooth surface as well as carbon abundance in space and laboratory dusty plasmas. The energetic dependences of a secondary electron yield along the grain curved surface and from a planar graphite substrate are reported. We have observed the grain yield to increase quadratically as a function of an angle of incidence. A ratio of the integral grain yield to the bulk value for glassy carbon was found to be 2.23. The established second crossover energy (900 eV for a clean surface) is in a good agreement with other single isolated dust grain experiments. Our preliminary measurements of a low-energy part of the secondary electron spectrum have revealed its Maxwellian shape (with the main maximum at 2.5 eV) with tiny subsidiary maxima in the 11–15 eV range.