159 10
is applied (. Fig. 10.14b), the SE signal at the edges of fea-
tures will be substantially enhanced.
Making Fewer BSEs, SE 2 , and SE 3
by Eliminating Bulk Scattering
From the Substrate
For the important class of specimens such as nanoscale parti-
cles which have such small mass thickness that the beam elec-
trons penetrate through the particle into the underlying bulk
substrate, the large BSE, SE 2 and SE 3 components that
dominates the E–T(positive bias) signal respond to substrate
properties and don’t actually represent specimen information
at all. Thus, the high resolution imaging situation can be sig-
nificantly improved by eliminating the bulk substrate. The
particles are deposited on an ultrathin (~10-nm) carbon film
supported on a metal (Cu, Ni, etc.) grid. This grid is placed
over a deep blind hole drilled in a block of carbon that will
serve as a Faraday cup for the beam electrons that pass though
the particles, as shown schematically in. Fig. 10.15a. An
example of this preparation is shown for particles of SRM470Grid bar,
e.g., Cu10 nm
carbon foil~10 nm carbon or high-d metal
coating for discharging and stabilityDeep
blind
hole in
carbonEverhart-Thornley
detectorGrid bar,
e.g., Cu10 nm
carbon foil~10 nm carbon or high-d metal
coating for discharging and stabilityEverhart-Thornley
detectorOn-axis
bright field
detectorAnnular
dark-field
detectorab. Fig. 10.15 a Schematic illus-
tration of specimen mounting
strategy to minimize background
by eliminating the bulk substrate.
b Scanning transmission electron
microscopy (STEM) two compo-
nent detector for high energy
electrons: on-axis bright-field
detector and surrounding annu-
lar dark-field detector
10.5 · Achieving High Resolution with Secondary Electrons