[3dem] [TEM] amplitude contrast

[Bill & Sue Tivol]

> On Aug 16, 2017, at 12:52 AM, Philip Koeck <Philip.Koeck at ki.se> wrote:
> 
> Just one question: When you say “absorption” of the electron wave to describe the imaginary part of the atomic scattering factor, how would you picture this absorption?
> What is actually happening when the wave amplitude decreases, (which should mean that the number of electrons decreases.)
>  
Hi Phillip,
	In answer to your question, electrons are not actually absorbed—that would require either inverse beta decay or interaction with a positron (or some even more bizarre process).  Electrons removed from the beam after interaction with the specimen are accounted for by the imaginary part of the amplitude.  They can be scattered to large enough angles that they do not enter the detector or suffer energy loss sufficient to have the bottom half of the lens system, perhaps including an imaging filter, to focus them to a point not within the detector.  They can also, of course, be focussed to a point on the detector that does not correspond to the proper imaging point, causing blurring or other noise events.  These removal processes are described by a decrease in the wave amplitude.
						Yours,
						Bill