Thon ring patterns with FEI Falcon and Gatan US4000

We are testing our new direct electron detectors (FEI Falcon and Gatan K2 Summit). Rachel Ruskin in the lab started comparing Thon ring patterns (see attachments) calculated from images of amorphous carbon film using the Falcon detector and Gatan US4000 CCD (scintillator-based):

Microscope:	FEI TF20
Voltage:	200 kV
Magnification:	29,000

Dose rate:
Falcon:		30 electrons/Å2/second
US4000:		25 electrons/Å2/second

Exposures:
Falcon:		0.4 sec, 1.0 sec, 5.0 sec, 7.5 sec
US4000: 	0.4 sec, 1.0 sec, 5.0 sec, 10.0 sec, 20.0 sec, 40 sec

Dose/pixel:
Falcon:		12, 30, 150, 225 electrons
US4000: 	10, 25, 125, 250, 500, 1000 electrons

Although the dose values are not exactly the same in these two exposure series it is clear that the Falcon shows Thon rings that extend all the way to Nyquist (see 7.5 second exposure) while the stop about 0.8 Nyquist in a similar image recorded using the US4000 (see 10.0 second exposure).

We will perform more tests, including the K2 Summit and film and will also perform quantitative assessments by measuring DQEs.