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excess of SEs compared to the bulk interior. In addition,

there will be enhanced escape of BSEs near the edge, and

these BSEs will likely strike other nearby specimen and

instrument surfaces, producing even more SEs. All of the

signals collected when the beam is placed at a given scan

location are assigned to that location in the image no matter

where on the specimen or SEM chamber those signals are

generated. The apparent SE emission coefficient when the

beam is placed near an edge is thus greatly increased over

the bulk interior value, often by a factor of two to ten

depending on the exact geometric circumstances. The edges

of an object will appear very bright relative to the interior of

the object, as shown in. Fig. 10.5 (e.g., objects in yellow

circles in. Fig. 10.5b) for particles of TiO 2. Since the edges

are often the most important factor in defining a feature, a

contrast mechanism that produces such an enhanced edge

signal compared to bulk is a significant advantage. This is

especially true considering the limitations that are imposed

on high resolution performance by the demands of the

Threshold Current/Contrast Equation, as discussed below.

10.4.2 Even More Localized Signal: Edges

Which Are Thin Relative to the Beam

Range

The enhanced SE escape near an edge shown in. Fig. 10.4

is further increased when the beam approaches a feature

edge that is thin enough for penetration of the beam elec-

trons. As shown schematically in. Fig. 10.6, not only are

additional SEs generated as the beam electrons emerge as

“BSEs” through the bottom and sides of the thin edge

100 nm

a b

100 nm EHT = 5.00 kV

WD = 1.4 mm

Signal A = InLens

Mag = 151.08 K X

Date :30 jul 2015

Time :17:54:00

. Fig. 10.5 a SEM image at E 0 = 5 keV of TiO 2 particles using a through-the-lens detector for SE 1 and SE 2 (Bar = 100 nm). b Note bright edge
effects and convergence of bright edges for the smallest particles (Example courtesy John Notte, Zeiss)

SE 1

SE 1

SE 1 SE (^2) SE 2
SE 1
SE (^2) SE 2
SE 2
BSE SE 2
SE 1 BSE SE 1
BSE
SE 1
SE 2
SE 2
BSE
BSE
BSE BSE
BSE

. Fig. 10.6 Schematic diagram
of the enhanced BSE and SE pro-
duction at an edge thin enough
for beam penetration. BSEs may
strike multiple surfaces, creating
several generations of SEs

Chapter 10 · High Resolution Imaging