Authors:  C. Swanson, I.D. Kaganovich

Abstract:  Complex  structures on a material surface can significantly reduce total  secondary electron emission from that surface.  A velvet is a surface that consists of an array  of vertically  standing whiskers.   The  reduction occurs  due to the capture of low-energy, true  secondary electrons emitted  at  the  bottom of the  structure and  on the  sides of the velvet whiskers.   We performed  numerical  simulations  and  developed  an  approximate analytical model that calculates  the net secondary  electron  emission yield from a velvet surface as a function  of the  velvet whisker length  and packing density,  and the angle of incidence of primary  electrons.  We found that to suppress  secondary electrons,  the  following condition  on  dimensionless parameters must be met: (π/2)DA tan θ>>1, where  θ is the  angle of incidence  of the  primary  electron  from the normal,  D is the fraction  of surface area taken  up by the velvet whisker bases, and A is the aspect  ratio,  A ≡ h/r, the  ratio  of height  to radius  of the  velvet  whiskers.  We find that velvets available today can reduce the secondary electron  yield  by 90% from  the  value  of a flat  surface. The values of optimal velvet whisker packing density that maximally  suppresses  secondary  electron  emission  yield are  determined as a function  of velvet  aspect  ratio  and electron  angle of incidence.

Submitted to: Journal of Applied Physics
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