Neue Methode zur Erfassung der Füllstoffverteilung innerhalb von Polymer-Verbundwerkstoffen mittels Rasterelektronenmikroskopie
Final Report Abstract
Quasi three dimensional SEM visualization of CNT is realized by voltage contrast imaging of CNT/epoxy composites. The CNT contrast is observed to invert two times as the accelerating voltage increases from 0.3 to 15.0 kV. At 0.7 kV the CNT contrast shifts from bright to dark, and after 1.5 kV bright CNT are observed again. The contrast inversion and imaging mechanism of CNT are interpreted: The epoxy is positively charged at 0.3-0.6 kV, electrons are therefore supplied through the CNT to neutralize the positive charges in epoxy. These electrons lower the potential of CNT and neighbouring epoxy, and enhance the local SE yield. On the contrary, epoxy is negatively charged when the voltage is above 1.5 kV. The injected PEs are trapped in the CNT, which also enhances the SE emission and generates a bright CNT contrast. Two possible explanations (weak PE-CNT interaction and slight charging of epoxy) are proposed for interpreting the dark CNT contrast at 0.7 and 1.0 kV. CNT visibility greatly depends on the following aspects: CNT dispersion, CNT concentration, accelerating voltage. Well dispersed CNT are easily visualized in the composites, while inhomogeneous dispersion of CNT leads to charge up of the epoxy-rich region and makes individual CNT invisible. The image contrast is enhanced by incorporating more CNT or by adopting higher accelerating voltage during observation.
Publications
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Imaging mechanism of carbon nanotubes on insulating and conductive substrates using a scanning electron microscope. Journal of Materials Science, 46 (2011) 7672-7632
W. Li, Y. Zhou, H. J. Fitting, W. Bauhofer
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Imaging of CNTs in a polymer matrix at low accelerating voltages using a SEM, Carbon, 49 (2011) 3891-3898
W. Li, W. Bauhofer
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The imaging mechanism, imaging depth, and parameters influencing the visibility of carbon nanotubes in a polymer matrix using a SEM, Carbon 49 (2011) 1955-1964
W. Li, S. T. Buschhorn, K. Schulte, W. Bauhofer
