Re: Does electron beam hit vertically in SEM at all the sample points
- From: Gary G <see.signature@bottom>
- Date: Fri, 17 Oct 2008 10:44:20 -0700
On Wed, 1 Oct 2008 10:58:53 -0700 (PDT), nutannathsharma@xxxxxxxxx
wrote:
Scanning coils deflect the electron beam so that the beam can reach
different points on the sample. However, I was wondering if that will
mean that the electron beam is not hitting all the points on the
sample at the same angle. That is to say, at the center point, the
beam will be hitting the sample vertically whereas at a point on the
periphery of the sample the beam will be slanted, albeit by a very
small amount. Could any body tell me whether I am right or wrong.
Nutan
The electrons are not travelling in a straight line but rather are
circular. Additionally, the electron optics will have three
conflicting variables that make imaging more 3-D specimens a
challenge. These are probe diameter, probe current and convergence
angle. As the beam is deflected (scanned) across the specimen, the
convergence angle will change. This convergence angle is the half
angle that the cone of electrons at the specimen makes with the center
line of the beam. In a sense, since each electron does not hit the
specimen at exactly the same point each time, the diameter of the
spiral of electrons creates the electron cone and thus the convergence
angle (sometimes called the divergence angle).
If the beam path was a line, then the points on the specimen would be
hit at different angles. However, since the beam is a spiral of
electrons, it would seem that every electron hits the specimen from an
angle. As the electron optics' parameters are changed, this angle
would also change.
gary g.
Kiss French. Drink California.
gary at gaugler dot com
.
- References:
- Does electron beam hit vertically in SEM at all the sample points
- From: nutannathsharma
- Does electron beam hit vertically in SEM at all the sample points
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