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MDS Alignment
All 3 modes have their own alignment
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Photo Mode**Press MDS PHOTO button**
Set up all imaging conditions:
• Spot Size (1 or 2)
• Alpha Angle (2 or 3)
• Magnification (40-60k)
• Dose (15-20 e-/Å2/sec)
After you set up dose, record your C3 lens value so that you can find the correct dose without having to recalculate it
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How to calculate specimen and image dose and dose rate
Example:
Io = 15 e/Å2/sec
Mi = 40,000x
If M s = 1.25 for screen
1 piAmp/cm2 = 625 x 10-12 e/Å2/sec
Is = 23.4 PiAmp/cm2
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Relationship of dose or dose rate between object and detector
Object intensity = I0 = Ii Mi2
Ii = I0/ Mi2 Ii = Is/ Ms
2
Screen intensity = Is = I0 Ms2/ Mi
2
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Dose Calculation (e-/Å2/sec)
Go to a completely open area (no ice or carbon, just vacuum)
Go to 50,000x Magnification
*Your dose at 50k in pA/cm2 is equal to
the dose in e-/Å2/sec
Adjust the following settings to obtain the
desired dose for your sample:
• Size of your beam (using Brightness knob)
• Spot Size
• Exposure time
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MDS Focus
**Press MDS FOCUS button**
Should be set up the same way as MDS PHOTO
• Be in MAG 1
• Select desired spot size, alpha angle and magnification
*generally these settings should all the be same as the settings in PHOTO mode
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MDS Search
**Press MDS SEARCH button**• Go to MAG 1
• Repeat Voltage Axis Alignment
• Go to Spot Size of 5 (you may also have to do the spot size alignment at this point if they are misaligned)
• Spread beam clockwise (using Brightness)
until you hear a beep
• Press SA DIFF
• Adjust DIFF FOCUS knob until the beam
is the desired size
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Aligning MDS Photo and MDS Search
• After setting up MDS SEARCH mode, go back to MDS PHOTO
• Find an area of interest such as ice contamination
• Center that area in Photo mode using the trackball
• Press MDS FOCUS
• Press MDS SEARCH
• If the area of interest is not in the center than press PLA and use your DEF/STIG X and Y knobs to bring the area to the center
• Turn off PLA
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Alignment of Search Mode
Photo Mode Misaligned Search Mode:Use PLA & def/stig x y to center area of interest
Aligned Search Mode