Modeling of Reduced Effective Secondary Electron Emission Yield from a Velvet Surface

摘要

Complex structures on a material surface can significantly reduce totalsecondary electron emission from that surface. A velvet is a surface thatconsists of an array of vertically standing whiskers. The reduction occurs dueto the capture of low-energy, true secondary electrons emitted at the bottom ofthe structure and on the sides of the velvet whiskers. We performed numericalsimulations and developed an approximate analytical model that calculates thenet secondary electron emission yield from a velvet surface as a function ofthe velvet whisker length and packing density, and the angle of incidence ofprimary electrons. We found that to suppress secondary electrons, the followingcondition on dimensionless parameters must be met: {\pi}/2 DA tan {\theta} >> 1where {\theta} is the angle of incidence of the primary electron from thenormal, D is the fraction of surface area taken up by the velvet whisker bases,and A is the aspect ratio, A {\equiv} h/r, the ratio of height to radius of thevelvet whiskers. We find that velvets available today can reduce the secondaryelectron yield by 90% from the value of a flat surface. The values of optimalvelvet whisker packing density that maximally suppresses secondary electronemission yield are determined as a function of velvet aspect ratio and electronangle of incidence.