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.

C 1.5 Condenser 1 (centering)
C 1.51 Set magnification selector to IOOx
Set C1 switch (5.23) to step 3
-
Turn C2 switch (1.25) - fully clockwise (overexcitation)
C 1.52 Switch on C1 (3.11): - Decentered bright spot appears
C 1.53 Turn C2 switch anti-clockwise until spot size is approximately
equal to small screen
C 1.54 Use Cf alignment screws (10.13) to center spot on screen
C 1.55 Set magnification selector to 1,000x
Repeat C 1.53 and C 1.54 until obtaining minirmun spot size
Set magnification selector to 6,300~
Center bright spot acc. to C 1.54
C 1.56 Repeat final check as in C 1.45
If necessary, compensate for illumination astigmatism by means of C2
stigmator (cf part
B)
Important: If C1 was strongly disaligned, recheck C2: switch off C1;
recenter C2 acc. to C 1.45; switch on C1 (step 3). At
6,300~recenter acc. to C 1.54
Note: Upon changing C1 setting (5.23) minimum spot may be slightly
- -
displaced. Correct - this displacement with beam alignment knobs,
not with
C1 alignment screws.
-

C 1.6 Objectivelensalignment
Prerequisite: Microscope column completely assembled and pumped down,
no previous lens alignment.
C 1.61 Fitting the centering screws
Ventilate column
Use adjustable two-pin wrench
(1 2.1 1) to unscrew blind screws (1 - 0.7)
Disassemble centering screws:
Disengage rotary knob
(I) from right-hand thread by turning anti-
clockwise, pull out until meeting resistance,
disengage from left-hand thread by turning clockwise, and pull out
Check cleanliness of gaskets on fixing sleeves
(2)
Fully screw in fixing sleeves (2) into holes (10.7) - by means of metal
plate (12.10)
Screw in rotary knobs
(1): turn anti-clockwise, push in, turn clockwise
until just meeting resistance
Open column at separation position
4
(cf part D)
Demount top cooling plate (3) (cf part D)
Loosen 3 fixing screws
(4, Allen M 4)
by one turn: upper polepiece
(pole plate) now displaceable
Close column and pump down without inserting cooling plate.
C 1.62 Further preparatory steps
Switch off all lenses
- keys on left alignment panel
Fully withdraw all apertures
- coarse drives fully anti-clockwise
Turn beam current selector (1.23)
- fully anti-clockwise (minimum current,
avoiding over-irradiation of screen)
Set high-voltage selector to 60
kV
Switch on beam - keys (1.16) - and (1.17)
-
Lock in specimen ("holey" film): shadow image of grid appears
Set both specimen drives to approx. 500 (digital indicators (2.2),
- (6.2)) -
Using beam alignment knobs, center bright spot (shadow image of P2 bore)
on screen and adjust for optimum brightness: This intensive bombardment
of screen permissible for a few seconds only.
C 1.63 Objective coarse alignment
C 1.631 Set magnification selector to lOOx (0.1)
C 1.632 Switch on objective (normal polarity, lamps (3.13) - and (3.14) - out)
Observe sweep direction of image detail rich in contrast (e.g. grid
mesh corner)
C 1.633 Use objective alignment screws (10.7)
- to recenter image detail

C 1.634 Set magnification selector to 1,000x: image detail again displaced
C 1.635 Center image detail on screen again with alignment screws (10.7)
-
,'
C 1.636 Switch off objective: image shrinks, roughly centrally, toward
screen center, but note possible sweep curve
C 1.637 Switch on objective
Alternately use specimen displacement drives and alignment screws
(10.7) to minimize sweep curve
-
C 1.638 Finally switch on objective again
C 1.64 Objective fine alignment
C 1.641 At
1,000~ focus circular image detail (approx. 0.5 mm dia. = 1/4 length
of center mark, hole in supporting film or particle)
Center detail on screen with specimen displacement
C 1.642 Check axial specimen position: focus should be obtainable with "Coarse"
knob (5.21)
- in its central position (max. deviation + 3 steps)
Otherwise check position of specimen grid in cartridze
C 1.643 Beginning in focusing position of "Coarse" knob, turn
- + 5 steps and
note current center (center point of image rotation)
C 1.644 Use alignment screws (10.7) to displace current center (image detail
coinciding with current center) toward screen center
Use specimen displacement to recenter image detail on screen.
C 1.645 Repeat C 1.643 and C 1.644 until current center coincides with image
detail centered on screen
C 1.646 Insert 200 um condenser aperture
(10.10) and, at IOOx, center on image
detail: this avoids over-irradiation of screen upon subsequently
switching off objective (cross-over image)
Switch to 1,000x again
C 1.647 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 maximum brightness (Check for this: turning each
beam alignment knob back and forth results in equal loss of bright-
ness both ways)
If aperture image is hereby displaced, recenter acc. to
C 1.646.

C 1.648 Switch on and off objective several times, each time repeating C 1.647
until
"star point" S practically coincides with image detail
Note this point P (plus
- polarity).
C 1.65 Polaritv reversal center
C 1.651 Switch off objective (3.13), - reverse polarity (3.14), - switch on (3.13) -
Important: Avoid reversal without switching off, otherwise electronic
switch will interrupt objective current for approx. 20 sec.
C 1.652 Note new location M (minus -
polarity) of image detail observed before.
C 1.653 Reverse polarity again (switch off, reverse polarity, switch on):
image detail again located at point P.
C 1.654 Use specimen displacement to move image detail half the distance from
P toward
M.
Repeat C 1.651 through C 1.654 until image detail stays at exactly
the same point when polarity
is reversed: this polarity reversal
center
U may be up to 1.5
mm (114 length of center mark) off screen
center in any direction.
C 1.66 Precision alignment on current center (normal polarity)
C 1.661 Turn "Coarse" knob (5.21)
-- + 3 steps from focus and note new current
center
D.
C 1.662 Turn objective alignment screws (10.7)
- very slightly to move current
center
D toward U.
After every small move check result acc. to C 1.661.
Important: This polepiece displacement strongly influences position
of current center
D and very weakly that of polarity
reversal center
U.
Good objective lens alignment is achieved if polarity reversal center U
(cf C 1.654) coincides with current center D (cf C 1.661, normal polarity)
and if
"star point" S (cf C 1.647) is very close to U.
Possible distance of U from screen center < 1.5 mm.
-
Quick check-up with
ltl 100 method" (EM 10 A/B)
Switch on C 1
(3.11) and set to step 4 or 5 (5.23) -
High voltage 60 kV
Set objective to 1100 (6.3) -
Check caustic patterns of both objective polarities:
(3.13) - wait for 5 sec. - (3.14) - wait for 5 .sec. - (3.13)
- -
Caustic patterns should coincide, distance - < 1.5 mm
Objective centering terminated.

C 1.68 Fixing the aligned polepiece
Keep objective lens switched on
Set high-voltage selector to 100 kV (maximum objective current)
Ventilate column
Open column at separation position 4 (cf part D)
Cautiously thighten 3 fixing screws (4) alternately without
causing any displacement of pole plate.
Important: Keep iron or steel tools carefully away from polepiece
bore
- polepiece easily damaged by magnetically attracted
tool
Place top cooling plate (3) on copper studs
(5) and fixwith 3 brass
screws (cf part D)
. .
Turn alignment screws (10.7) - anti-clockwise, pull out until meeting
resistance, turn clockwise, and withdraw
By means of metal plate (12.10) unscrew fixing sleeves
(2) and remove
Screw in blind screws (10.7)
- with adjustable two-pin wrench
(1 2.1 1)
Close column and pump down.
C 1.69 Final check:
Acc. to C 1.67, check whether objective alignment has remained un-
changed after removal of alignment screws. Otherwise pole plate-
displaced during tightening of fixing screws; alignment must be
reneated.