Zeiss EM 10 A User manual

Electron Microscope EM

Operating Instructions, Part C

Alignment

Lens Alignment

C 2. Aperture Alignment

Beam Alignment

Centering Objective Lens Stigmator

Lens alignment

1.1

Possible alignment procedures

Alignment of the EM

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.

Projector 2 (centering)

C 1.21 Set beam current selector to step

(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

(

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

(maximum value)

1.24

Focus image detail with "Coarse" knob (5.2

)

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.

1.3 Projector

(centering)

1.31 Switch onP1 with key (3.15)

Set magnification to 6,300~:

image detail in general not centered on

screen

1.32 Set rotary switch (5.22)

to "Diffr." and focus central diffraction spot

with knob (5.22)

1.33 Use PI aligment screws (10.2)

to place diffraction spot on polarity

reversal center

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)

1.35 Set magnification to 20,000~and note direction of image sweep

Switch back to

6,300~

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

1.37 Repeat

1.32 through

1.36 (increasing upper magnification

value in

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

1.24 and

1.25; switch on

P1. In general, recentering acc. to

1.33 will

suffice.

1.4

Condenser 2 (centering)

Prerequisite: aligned imaging lenses

1.41

Optimize beam aligment

Set beam current selector to step

(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

.2)

Set magnification selector to

1,000~

Switch off objective: "star point"

(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

switch (1.25)

fully anti-clockwise (minimum current)

C 1.43 Switch on C2 (3.12):

in general, decentered bright spot appears

1.44

Turn

switch clockwise: bright spot moves away from center.

1.45 Use

aligment screws (10.12) to recenter bright spot on screen

Repeat

1.44

and

1.45 until obtaining minimum spot size

This completes centering of condenser

Final check: Upon fully turning

switch (1.25)

both ways bright spot

grows and shrinks, remaining centered on screen center.

(tilting) (required only if final check is not satisfactory or after

disassembling

C2)

1.46 Turn

switch clockwise from minimum spot setting

(C2

over-

excited) and note sweep direction of growing spot

Reset

switch for minimum spot size

1.47 Use

tilting screws

(10.11)

to displace bright spot

sweep direction

Important: Loosen at least one of the screws

(10.11)

before

tightening any of the others.

1.48 Recenter spot by means of

aligment screws (10.12)

do not

use beam alignment potentiometers for this

Repeat

1.46

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.

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