Why FEG?

[max.sidorov at spansion.com]

Yes, Uwe is exactly correct. The energy spread is what makes the difference here. Plus low mag and large underfocus. And it applies to the info limit, not to point-to-point resolution. See an example at http://maxsidorov.com/ctfexplorer/science/spatial_coherency.htm (two pictures at the bottom).
 
 
Max


________________________________

	From: Lucken, Uwe [mailto:uwl at nl.feico.com] 
	Sent: Friday, April 23, 2004 6:03 AM
	To: Philip Koeck; 3dem at ucsd.edu; microscopy at sparc5.microscopy.com
	Cc: Sidorov, Max
	Subject: RE: Why FEG?
	
	

	Dear Philip, for an FEG one can set 0.6eV energy spread and for and Lab6 one usually has 1.5eV energy spread. As you can see for -2000nm defocus and 61kx. There is a small mistake in the estimate of the convergence angle. The parallel beam conditions are C2 diameter/7 in microprobe and I have included the plots. 

	 

	end

	Sincerely yours,

	 

	Dr. Uwe Lücken

	Senior Scientist Application Development

	FEI-Electron Optics; Building AAE

	Achtseweeg Noord; 5600 MD Eindhoven

	The Netherlands

	tel.:+31-40-2766106; fax:+31-40-2766102

	mob: +31 40 2791621

	 

	-----Original Message-----
	From: Philip Koeck [mailto:Philip.Koeck at biosci.ki.se]
	Sent: Friday, April 23, 2004 10:44 AM
	To: 3dem at ucsd.edu; microscopy at sparc5.microscopy.com
	Cc: Max.Sidorov at Amd.Com; Lucken, Uwe
	Subject: Why FEG?

	 

	Hi,

	 

	I've been playing around with Max Sidorow's CTFexplorer and I'm finding it hard to see the
	advantage of FEG microscopes for structural biology.

	At 61000-times magnification I can't see any major difference between the Tecnai 20T and
	the Tecnai F20T for example.

	Only at magnifications beyond 300000 is the F20T clearly superior (due to better spatial
	coherence).

	 

	Am I (or is CTFexplorer) missing something relevant?

	 

	The CTFexplorer can be found at http://clik.to/ctfexplorer.

	Upon request I can also send a Word file with the CTF-plots.

	 

	Philip

	 

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