Hi, researchers,
In the book about TEM, it is mentioned there are two kinds of angle, the incident angle and the convergence angle.
the former is that between the normal of a specimen plane and the incident electron beam. the latter is that convergent electron beam illuminates a specimen, the semi-angle of the cone is termed "convergence angle."
Is there any difference between the two kinds of angle?
Hi there,
When a light ray interacts with a surface, we draw a normal line perpendicular to that surface.
The angle of incidence is the angle between a light ray and the normal when the ray hits the surface (directed towards the surface)
The angle of reflection is the angle between a light ray and the normal when the ray leaves the surface (directed away from the surface).
Regards,
Angle of incidence is in general the angle that ray of light makes with the surface of the object,
Critical angle is specifically the minimum angle of incidence for which the ray doesn't go through the refracting object.
As the angle of incidence is increased in little steps from 0 degrees there comes a time when the light wave doesn't go through the surface.
Another thing to be noted from this definition is the "minimum" word. Even after attaining critical angle the angle of incidence when increased won't allow light wave to go through the surface of the object. And all such angles won't be called critical angle.
Only the minimum angle for which the light wave does not leave one medium and enters another medium is termed the critical angle.
Incident angle - angle between beam and specimen; for TEM it is most often equal to 90 degrees.What is a convergence angle you can see from picture on this page (actually, it is more important for STEM operation):
http://www.microscopy-analysis.com/editorials/editorial-listings/how-optimize-your-eels-experiments-adjusting-collection-angle-your
@ Francisco Mesa Linares ·, Qhatan Adnan Yousif, Ali hadi Ghawi
Why you are giving answers on question you do not understand?
Dear Vladimir Dusevich, thanks for your answer.
Can it be understood like that, in STEM operation, the sum of incident angle and convergence angle is 90?
In STEM, due to the larger probe forming aperture, the incident angle is smaller than that in conventional TEM. Is it right?
In most cases incident angle for TEM and STEM is 90 (common exemptions - when you work with EDS or tomography). Convergence angle does not depend on incident angle, for STEM (and SEM) it is an angle which describes trajectories of outer electrons of an electron beam when the beam is focused on specimen surface.
got it.
Thanks very much for your detailed explanation.
@Vladimir Dusevich
Dear Lewis,
I would like to add a brief manuscript comimg from a Mozart's lecture I gave in Rovereto, Italy in 2012 at the meeting of Mozart' italian association. I focused to some compositions.I feel sorry for the italian text.
good vacation
Giacomo
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