Low-Energy Focused Ion Beam Milling Provides
Reduced Damage During TEM Sample Preparation
gatan gets it
Laurent Roussel
Product Marketing Manager SEM & DualBeam, FEI, Hillsboro, OR, 97124
laurent.roussel@
fei.com
Introduction
Two sites of interest are identifi ed on the LaB
6
emitter
Th e combined focused ion beam (FIB) and scanning
(Figure 2a): the apex, exposed to heavy particle bombardment
The most
electron microscope (SEM), known as the DualBeam, is
during its lifetime, and the signifi cantly less-exposed emitter
well-known for its unique ability to produce site-specifi c thin
side. From each site, aft er protecting the sample surface using
advanced
samples starting from bulk and then attaching the section to
beam-induced deposition of platinum, a thin sample was
a transmission electron microscope (TEM) grid, all in-situ. It
prepared using diff erent pre-thinning techniques. Finally, both
imaging filters
To learn more,
has been reported that producing a thin sample using a 30 kV
samples were thinned using increasingly lower FIB energies.
gallium FIB creates surface damage several tens of nanometers
Th e fi nal step consisted of a 2-kV FIB polishing step.
deep. However, recent DualBeam technology improvements
Most of the protective platinum was removed, and some areas
are here
visit us at
now enable the FIB to produce thin samples with a thickness
near the actual sample surface showed very high electron
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well below 50 nanometers and deliver a tightly focused ion
transparency (Figure 3). Although assessing the sample quality
beam at an energy of 2 kV and below, which dramatically
is premature at this point, this work already demonstrates
reduces the damage depth to as low as 1 to 2 nanometers in
the fl exibility off ered by DualBeams for very thin sample
typical materials, such as silicon.
preparation, as well as their site specifi city and end-pointing
GIF Quantum
null
One example of a challenging application being addressed
capabilities. Both samples were then transferred to the TEM,
with this capability is the failure analysis of LaB
without further preparation.
6
emitters.
LaB
6
emitters are widely used in electron microscopy as
high-brightness electron sources, owing to their favorable
HR-TEM Microscopy Study on LaB
6
properties for thermionic emission: low work function and
High-resolution TEM is an excellent method to study the
high melting point. Th e emitter consists of an LaB
structure of materials at the atomic level. In combination with
6
single
crystal with a carefully shaped tip (Figure 1).
spherical aberration (C
s
) correction, HR-TEM images directly
During its lifetime, an LaB
visualize the atomic order of crystals, and determination of the
6
emitter can undergo diff erent
types of failure. Some failures can be related to a source in
atomic positions in the image is usually straightforward. Th e
manufacturing (mechanical failure, defect in the crystal, etc),
most limiting factor for the determination of atomic positions
others to its operation (for instance, overcurrent, which may in C
s
-corrected images is the thickness of the sample in the
lead to mechanical failure), or to its environment. In the latter electron beam direction.
1000 spectra per second
case, bad vacuum will cause gas molecules in
the gun to be ionized by collisions with the
electron beam. Th e positive ions thus formed
1 nulls Electrostatic Shutter
are accelerated towards the emitter and may
sputter away the cathode material.
30 fps Imaging
Sample Preparation of LaB
6
on the
DualBeam
Characterizing the LaB
9 mm Aperture
6
emitter by
means of high resolution TEM (HR-TEM)
requires from one to several thin samples
DualEELS
null
to be prepared, which must meet certain
criteria: the preparation of each sample
should be site-specifi c and deliver lamellas
Automated Acquisition Software
with a thickness well below 50 nm and of
highest possible quality.
Th e work described here was performed
on a Helios NanoLab DualBeam (FEI
Company, Hillsboro, OR). Its high-stability
platform, sub-2 kV FIB mode, and integrated
in-situ preparation capabilities are useful for
preparing high-quality thin sections.
Figure 1: LaB
6
emitter overview, SEM image.
40 doi: 10.1017/S1551929509000364
www.microscopy-today.com • 2009 September
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