Characterization of Nonconductive Polymer Materials Using FESEM
Y.D. Yu*, M.P. Raanes and J. Hjelen
Laboratory of Electron Microscopy, Department of Materials Science and Engineering, Norwegian
University of Science and Technology, NO-7491 Trondheim, Norway
*corresponding author, yingda.yu@material.ntnu.no
One of the most challenging SEM characterization areas at our Electron Microscopy Lab [1] is
currently found for characterizing nonconductive nano materials, especially for increasing demands
from nano polymer research. This article gives an overview of using our Zeiss Ultra 55 and Supra
55VP SEMs for characterization of un-coated nonconductive materials.
For conventional SEM imaging of nonconductive materials, specimens need to be coated for
preventing the accumulation of electrostatic charge. However for porous nano-composite polymer
[2], sputter coating would potentially have the impact on SEM imaging of the nanoenhanced
particles. Fig. 1 shows a variable pressure (VP) SEM micrograph of the nano particle enhanced
polymer from Zeiss Supra SEM. The SEM chamber gas pressure was carefully controlled to 8 Pa for
achieving beam charge stabilization, and also for stabilizing the porous polymer by reducing
shirking under electron irradiation. VPSEM resolution is strongly limited by the complicated beamspecimen interactions, and only the VPSE detector is available for SE imaging. To get higher
resolution low voltage SE imaging is applied for the relative condensed polymer-particle
characterization [3]. In low voltage mode by controlling the electron landing energy, a dynamic
charge balance can be built for the incoming and outgoing electrons on the sample surface. At 1 kV,
SE1 raises rapidly from a small interactive volume with a narrow angular distribution. Together with
using collecting-efficient through-the-lens (In-lens for Zeiss) detector, the resolution at low voltage
mode could reach at the nanometer level [4]. Fig. 2 shows a SEM micrograph of the polymer
particles from Zeiss Ultra In-lens detector at 3 kV with a working distance (WD) of 3 mm, where the
artifacts were caused from slightly over charging. As decreasing down to 1 kV and WD to 1 mm, the
dynamic charge balance was nearly reached as shown in Fig. 3, which is the enlargement of the
white rectangular region in Fig. 2. The horizontal streaks on the particles in Fig. 3 were also caused
by tiny over charging from 1 kV incident beam, which could be fully removed by further decreasing
to 0.5 kV as shown in Fig. 4. All of these micrographs were recorded by using a 10 μm in diameter
aperture to limit beam divergence, which gives benefits to reduce both the beam spherical and
chromatic aberrations, and further increasing depth of field at such a short WD. By using this
optimized setting with the detailed surface information, a series of nanoindentation tests were carried
out for understanding particle nano-mechanics [3].
Compositional characterization can also be performed at this low voltage mode by using the Zeiss
EsB detector [5] through filtering potential control for collecting only low-loss BSE signals. The
initial test result is shown in Fig. 5 with metallic coating, and the low-los BSE indicates coating
segregation to the triple junction with the filtering grid of 330 eV.
References
[1] Y.D. Yu et al., Proc. the 14th EMC, ISBN 978-3-540-85225-4. (s. vol.2) (2008) 513.
[2] L. Shao, PhD Thesis, Norwegian University of Science and Technology, Trondheim, 2008.
[3] J. Y. He et al., Journal of Physics D: Applied Physics, 42 (2009) 085405.
[4] D.C. Joy and C.S. Joy, Micron, 27 (1996) 247.
[5] K.W.Kim and H. Jaksch, Micron, 40 (2009) 724.
The 17th International Microscopy Congress, International Federation of Societies for Microscopy, Rio de Janeiro, 19. 09. 2010 - 24. 09. 2010
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M-11 Polymers, Molecular Crystals and Radiation-sensitive Materials
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Rio de Janeiro
Materials Science and Nanotechnology
Soft materials, including synthetic polymers, biological materials, and combinations of the two, can be structured
over a broad range o f length scales, an d this structure c an be studied by a variety of imaging methods such as
electron, X-ray, scanned-probe, and optical microscopies. Quantifying soft-materials structure, particularly at nano
length scales, remains a challenge, however.
Traditional methods of electron microscopy employ heavy element stains to generate Z-contrast. These have played
a key role in structure-property studies for de cades and continue to do so in problems involving, for example,
polymer blends, copolymers, and various types o f composite materials. I mportant alternative stain-free methods
continue to emerge. Phase contrast imaging, originally rooted in defocus techniques, is seeing renewed impact at
higher r esolution u sing e ither h olography o r one o f s everal new phase-plate approaches. D ifferential i nelastic
scattering between often similar soft-materials components can also be assessed spectroscopically.
Energy filtering and spectrum imaging, for example, have been increasingly used to solve soft-materials morphology
problems and can be implemented with nanoscale resolution using electrons or X-rays. These alternative approaches
have also enabled new experiments involving hydration/solvation using cryo or wet-cell techniques.
At the same time, however, the new instrumentation and new techniques available to the soft-materials community
has brought into increasingly clear perspective the fundamental limitations on the achievable dose-limited resolution
when using energetic ionizing radiation to probe soft materials. Given the advances over the past decade in efficient
detector technologies and rapid data-acquisition methods, these limitations increasingly center on the question of
how to extract meaningful information from datasets that are inherently noisy due to the finite exposure many
radiation-sensitive materials can withstand. This s ymposium will c oncentrate o n th e e merging n ew methods to
microscopically study so ft-materials m orphology, n ew m orphologies e nabled b y h ierarchically st ructured soft
materials, and new approaches to f urther enhance the achievable spatial resolution associated with dose-limited
imaging of radiation-sensitive materials.
Chairpersons:
Matthew R. Libera
Stevens Institute of Tecnology
Hoboken, NJ, USA
mlibera@stevens-tech.edu
Caribay Urbina
U. Central de Venezuela
Caracas, Venezuela
caribay.urbina@ciens.ucv.ve
Invited Speakers:
- Ray Egerton, University of Alberta, Canada
- Fernando Galembeck, Universidade Estadual de Campinas, Brazil
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