Scanning Electron Microscopy and X-Ray Microanalysis

99 6

. Fig. 6.7 a Schematic illustra-
tion of projection distortion of
tilted surfaces. b Illustration of
foreshortening of familiar objects,
paper clips (upper) Large area
image at 0 tilt; (lower) large area
image at 70° tilt around a horizon-
tal tilt axis. Note that parallel to
the tilt axis, the paper clips have
the same size, but perpendicular
to the tilt axis severe foreshorten-
ing has occurred. The magnifica-
tion also decreases significantly
down the tilted surface, so the
third paper clip appears smaller
than the first (Images courtesy
J. Mershon, TESCAN)

A

B

C

D

A* B* C* D*

In the SEM image, arrows spanning

A, B, C, D appear to be same length!

Projection

Distortion:

Foreshortening

Scan Rays

S*

Cross-section

through rough

specimen

a

Strue =

b

tilt

Tilt Axis

0

70 ºtilt

6.4 · Image Defects