Aperture Alignment

Imaging Conditions Au/C sample

• Scan rotation set 180 degrees so image motion matches piezo stage directions, plate handle at image bottom. Up/Down buttons move Up/Down, L/R buttons move R/L (reversed)
• To see Au grains of ~ 30 to 120 nm, need 10 to 50 kX mag (relative to 19/21 inch display)
• Working with 120 um aperture 3 nA mode
• Gun -53.0 -65.0
• App +54.1 +79.5
• Stig -23.7 +13.7
• WD 9.098
• Apparent Image Shift with increasing WD
• if Ax becomes more positive, shift direction becomes more left
• if Ay becomes more positive, shift direction becomes more vertical
• Wobble method:
• set wobble amplitude to 5%
• adjust Ax and Ay to minimize wobble
• problem, as you go through best value, phase reverses, hard to catch
• Manual Focus method:
• put manual cross hairs on a feature
• increase WD, see which direction feature moves
• if it moves right, increase Ax
• if it moves down, increase Ay
• if you change aperture position significantly, you will need to re-adjust WD and Stig to recover a sharp image
• once you have the best value, Au/C should look good, you can check with wobble method

Aperture 6, 120 um 3 nA

• Gun -53.0 +65.0
• Aperture +54.1 +79.5
• Stig -23.7 +13.7
• Stig Bal X upper 84.8 lower 100.0
• Stig Bal Y upper 71.3 lower 99.2

Changing to other current/condenser settings mainly changes WD

• For 3.0 nA, WD 9.098 stig -23.4 +15.2
• For 2.5 nA, WD 9.032
• For 2.0 nA, WD 8.986  stig -21.2 +15.8
• For 1.5 nA, WD 8.950  stig -19.5 +17.9  

Defocus of 10 nm is significant (should be less for smaller apertures)

Stig change of 1% is significant

Aperture 1, 60 um (on axis)

• Gun -2.5 -54.5
• App +0.5 +70.3
• Stig +2.0 +27.0
• Stig Bal X upper 84.1 lower 100.0
• Stig Bal Y upper 70.2 lower 99.8
• WD 200 pA 8.915

Other current settings

• Max WD  9.012  stig +14.2 +40.9
• 200 pA WD 8.915  stig +2.0 +27.0
• 100 pA WD 8.905 stig +1.9 +29.3

Aperture 5 90 um

• Gun +10.1 -6.7
• App -14.5 +20.6
• Stig +2.0 +5.7
• Stig Bal X upper 85.8 lower 100.0
• Stig Bal Y upper 69.7 lower 99.1
• WD 1 nA 8.954
• WD 800 pA 8.938 stig +2.2 +6.9

Aperture 3 30 um

• Gun =45.5 -45.2
• App -51.9 +57.2
• Stig +14.7 +2.5
• Stig Bal X upper 86.7 lower 100.0
• Stig Bal Y upper 71.7 lower 100
• 80 pA WD 8.941 stig +14.7 +2.5
• 60 pA WD 8.929 +15.0 +3.1
• 40 pA WD 8.922 +15. +6.0

 Apps 2 and 4, 20 um and 75 um cannot be aligned properly, out of range with current filament