Modeling of reduced effective secondary electron emission yield from a velvet surface

Complexstructures on amaterialsurface can significantly reduce totalsecondary electron emission from thatsurface. A velvet is asurface that consists of an array of vertically standingwhiskers. The reduction occurs due to the capture of low-energy, truesecondary electrons emitted at the bottom of thestructure and on the sides of the velvetwhiskers. We performed numerical simulations and developed an approximate analytical model that calculates the netsecondary electron emission yield from a velvetsurface as a function of the velvetwhisker length and packing density, and the angle of incidence of primaryelectrons. We found that to suppresssecondary electrons, the following condition on dimensionless parameters must be met:(π/2)DA tan θ≫1, whereθ is the angle of incidence of the primaryelectron from the normal,D is the fraction ofsurface area taken up by the velvetwhisker bases, andA is the aspect ratio,A ≡ h/r, the ratio of height to radius of the velvetwhiskers. We find that velvets available today can reduce thesecondary electron yield by 90% from the value of a flatsurface. The values of optimal velvetwhisker packing density that maximally suppresses thesecondary electron emission yield are determined as a function of velvet aspect ratio and theelectron angle of incidence.

Source: Journal of Applied Physics - December 5, 2016 Category: Physics Authors: Charles Swanson and Igor D. Kaganovich Source Type: research