Difference: CcdCalculations (5 vs. 6)

Revision 611 Sep 2007 - Main.BillRice

 
META TOPICPARENT name="CemParameters"
Contents

Tecnai F20

Procedure

  • Go to low-dose Exposure mode
  • Set beam intensity to 1 second exposure time
  • In SerialEM, set Record time to 1 second, with 1X binning
  • Take a Record picture and measure average intensity (counts/pixel)
  • In low-dose pullout tab, choose to measure intensity when screen is down and small screen is exposed (fully covered by beam)
  • This gives dose measured in electrons per square nm (ie mag taken into account)
  • From CCD calibration, convert square nm to pixels, get dose in electrons/pixel
  • Gain = counts per pixel / electrons per pixel = counts per electron

Tabulated data

Magnification Dose (e/nm^2) nm/pixel Dose (e/pixel) Counts/pixel Gain
5800 7.298 1.308 39.4 1151.3 29.2
Changed:
<
<
19000 199.2155   38.92 1169.99 30.06
>
>
19000 199.2155 0.442 38.92 1169.99 30.06
 
25000 342.9676 0.352 42.5 1162.54 27.36
29000 448.6993   39.31 1134.07 28.85
50000 1418.9582 .170 41.0 1205.6 29.40

Jeol 2100F

Procedure

  • 50K Mag, spot 5, set intensity to 10 pA/cm^2 (small screen)
  • Set gain on CCD to desired level
  • Insert and center SA Aperture #3; beam should now fully fit on small screen
  • Read screen current on small screen in pA/cm^2
  • Take a 1 second Exposure image
  • Using ImageJ? software, box out area inside exposed circle and measure average counts, sd
  • Determine pixel area covered by SA aperture as follows:
    1. import image into spider
    2. Using th m command, threshold at level of (mean - 5 standard deviations)
    3. Using Hi T command, measure average of thresholded mask calculated above
    4. Pixel Area = 2048*2048*avg intensity
  • Total counts = Avg counts * pixel area
  • Convert current to electrons as follows:
    1. Diameter of small screen = 2.5 cm - > area = 4.91 cm^2
    2. 1 sec exposure means 1 Coulomb per Ampere
    3. 1 elecron = 1.60 * 10^-19 C
    4. Electrons = (pA/cm^2 * 4.91 cm^2 )/ (1.6*10^-7 e/pA)
  • Gain = total counts/total electrons

  • area of SA #3: 1.16 * 10^6 pixels

Tabulated Data

Trial Mean Counts Total Counts Current (pA/cm^2) Electrons Gain (counts/electron)
Low 1 2896.8 3.36 *10^9 2.5 7.67 * 10^7 43.8
Low 2 2902.2 3.37 * 10^9 2.5 7.67 * 10^7 43.9
Low 3 2984.3 3.46 * 10^ 9 2.5 7.67 * 10^7 45.1
Low 4 2977.1 3.45 * 10 ^9 2.5 7.67 *10^7 45.0
High 1 11780 1.37 * 10^10 2.5 7.67 * 10^7 178
High 2 11750 1.36 * 10^10 2.5 7.67 *10^7 178

JEOL 3200FSC

Procedure

  • Similar to Jeol 2100F, but use SA aperture 3 and Entrance aperture 3

Tabulated Data

Aperture Area Avg counts Total Counts Current (pA/cm^2) Electrons Gain
EA 3 3.50 * 10^6 614.524 2.15 * 10^9 2.45 7.52 * 10^7 28.6
SA 3 3.48 * 10^6 614.294 2.14 * 10^9 2.40 7.36 * 10^7 29.1

  • Set ALLOWTOPICVIEW =

-- BillRice - 11 Sep 2007

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