Scanning Electron Microscopy and X-Ray Microanalysis

161 10

A simple STEM-in-SEM bright-field detector can be
created as shown in. Fig. 10.18. The grid carrying the thin
specimen is placed over an aperture that serves to stop elec-
trons that have suffered an elastic scattering event in the
specimen. The unscattered beam electrons pass through this
aperture and strike a gold-covered surface below, where they
generate strong SE emission, which is then attracted to the
E–T(positive bias) detector, creating a bright-field image. If
the SEM is also equipped with a TTL detector, the nearly pure
SE 1 image that arises from a thin specimen can be collected
with the TTL detector simultaneously with the bright-field

STEM image collected with the E–T(positive bias) detector,

as shown for particles supported on a lacey-carbon film in

. Fig. 10.19.

10.5.3 Eliminate the Use of SEs Altogether: “Low Loss BSEs“

“Low Loss BSEs“

BSEs are usually considered a low resolution signal because

of the substantial delocalization that results from multiple

elastic scattering of the beam electrons at conventional beam

Simple STEM-in-SEM detector

Short

working

distance, ~ 3 mm

Au surface

Through the lens detector: SE image

E-T detector: “STEM Image”

Electrons

scattered by

particle are

cut off by

aperture

Aperture

C-film and

support grid

Unscattered beam electrons

Scattered

beam

electrons

. Fig. 10.18 Schematic
cross section of a STEM-in-SEM
detector that makes use of the
Everhart–Thornley(positive bias)
detector to form a bright-field
STEM image

Aerosol particles collected on lacey carbon

25 keV cold-FEG-SEM

ab

SEM (TTL) STEM (ET)

500 nm

. Fig. 10.19 Aerosol contamination particles deposited on lacey-carbon film and simultaneously imaged with a TTL detector for SE 1 and the
STEM-in-SEM detector shown in. Fig. 10.18 (Example courtesy John Small, NIST)

10.5 · Achieving High Resolution with Secondary Electrons