Zeiss EM 10 A User manual

Electron Microscope EM 10
Operating Instructions, Part C
Alignment
C
I. Lens Alignment
C 2. Aperture Alignment
C
3. Beam Alignment
C
4.
Centering Objective Lens Stigmator
C
1. Lens alignment
C
1.1 Possible alignment procedures
Alignment of the EM
10 lenses in general remains constant for long
periods of time.
specially the objective lens alignment carried out
during manufacture will be retained precisely as long as the objective
lens is not disassembled.
Double condenser (Cl, C2) and double projector (Pl, P2) are of identical
design (cf. part A). Each of these four lenses can be displaced (against
a restoring spring) as a whole ("centering"). With C2 and PI, it is
possible in addition to displace one polepiece with respect ot the
other; this "tilting" of the lens axis is required only after disassembling
the double lens concerned and is carried out by three adjusting screws
(normally concealed) for which restoring springs are not provided.
Prerequisites for correcting the alignment of the double lenses are
correct objective lens alignment as well as precise alignment of both
the illumination direction and the condenser aperture with respect to
the objective lens axis. Procedures for checking these alignments are
described in the appropriate sections of the alignment instructions.

C 1 .2 Projector 2 (centering)
C 1.21 Set beam current selector to step
1 (minimum value)
Switch off all lenses except objective
C 1.22 Use specimen displacement drives to place image detail rich in
contrast on objective lens axis (polarity reversal center):
Place suitable image detail in screen center
Switch off objective (3.13)
-
Reverse objective polarity (3.14): - avoid reversal without switch-
ing off
Switch on objective (3.13):
- Image detail must appear at exactly
the same place as before
Otherwise, switch off objective, reverse polarity, switch on
again, and use specimen drives to move image detail to central
position between the two image positions.
Repeat polarity reversal until image detail appears in exactly
identical position with both polarities; this "polarity reversal
center" may be up to 1.5
mm ( = length of center mark) off screen
center.
From now on, do not change specimen position any more
C 1.23 Switch onP2 with key (3.16)
-
Set magnification selector (1.24) - to 6,300~(maximum P2 current)
Set beam current selector (1.23)
- to step 8 (maximum value)
C
1.24 Focus image detail with "Coarse" knob (5.2 1 )
-
Use P2 alignment screws
(10.1) to center image detail on small screen
-
C 1.25 Turn magnification selector from 6,300~to 1,000~: image detail must
shrink concentrically towards polarity reversal center.

C 1.3 Projector 1 (centering)
C 1.31 Switch onP1 with key (3.15)
-
Set magnification to 6,300~:
image detail in general not centered on
screen
.
C 1.32 Set rotary switch (5.22)
- to "Diffr." and focus central diffraction spot
with knob (5.22)
-
C 1.33 Use PI aligment screws (10.2)
- to place diffraction spot on polarity
reversal center
C 1.34 Set switch (5.22) - back to "Image"
This completes centering of projectors
Final check: Image detail centered at 100,000x shrinks concentrically
upon switching to 6,300~.
PI (tilting) (required only if final check is not satisfactory or after
disassembling PI)
C 1.35 Set magnification to 20,000~and note direction of image sweep
Switch back to
' 6,300~
C 1.36 Use PI tilting screws (10.3) - to displace image detail in sweep
-
direction by approx. half the sweep distance
Important: Loosen at least one of the screws (10.3) before
-
tightening any of the others
C 1.37 Repeat C 1.32 through C 1.36 (increasing upper magnification
value in
C 1.35 as aligment is improved) until image derail grows
and shrinks concentrically with screen center as magnification is
varied throughout range
Important: If PI was strongly disaligned, recheck P2: switch off
PI; recenter P2 acc. to C 1.24 and C 1.25; switch on
P1. In general, recentering acc. to C 1.33 will
suffice.

C 1.4 Condenser 2 (centering)
Prerequisite: aligned imaging lenses
C
1.41 Optimize beam aligment
Set beam current selector to step
1 (minimum value)
Switch off P1 and P2
Set magnification selector to lOOx
Insert 200 vm condenser aperture (10.10) and center on reversal
center (cf
C 1 .2)
Set magnification selector to
1,000~
Switch off objective: "star point" S (image of cross-over) appears
temporarily (just before objective current
= 0), then small shadow
image of condenser aperture
Use beam alignment potentiometers to center aperture image on screen
and to adjust for maxim brightness: turning each beam alignment
potentiometer back and forth results in equal loss of brightness
in both ways; if aperture image is displaced during this procedure,
recenter with condenser aperture drive.
Repeatedly switch on and off objective, each time recentering aper-
ture image and adjusting for optimum brightness until "star point" S
practically coincides with polarity reversal center and aperture
image is centered on it
Switch on objective,
P1, and P2
Do not touch beam alignment knobs again until completion of condenser
alignment.
C 1.42 Set magnification selector to
1,000~
Turn C2 switch (1.25) - fully anti-clockwise (minimum current)
C 1.43 Switch on C2 (3.12):
- in general, decentered bright spot appears

C 1.44 Turn C2 switch clockwise: bright spot moves away from center. ,
C 1.45 Use C2 aligment screws (10.12) to recenter bright spot on screen
Repeat
C 1.44 and C 1.45 until obtaining minimum spot size
This completes centering of condenser
2
Final check: Upon fully turning C2 switch (1.25) - both ways bright spot
grows and shrinks, remaining centered on screen center.
C2 (tilting) (required only if final check is not satisfactory or after
disassembling
C2)
C
1.46 Turn C2 switch clockwise from minimum spot setting (C2 over-
excited) and note sweep direction of growing spot
Reset
C2 switch for minimum spot size
C 1.47 Use
C2 tilting screws (10.11) to displace bright spot - in
sweep direction
Important: Loosen at least one of the screws
(10.11) before
-
tightening any of the others.
C 1.48 Recenter spot by means of C2 aligment screws (10.12) - do not
- -
use beam alignment potentiometers for this
Repeat
C 1.46 to C
1.48 until, upon over- and under-exciting
C2, bright spot grows and shrinks concentrically with screen
center. Increase magnification to 4,000~as alignment is im-
proved to obtain more exact alignment.