We have developed a platform that allows for real time optical sensing based on localized surface plasmon resonance (LSPR) readout inside a transmission electron microscope (TEM). With the TEM, we obtain insight into the structure and composition of materials by performing imaging and spectroscopy with atomic resolution [1]. However, the probed volume is rather small, and the beam-specimen interaction is often non-negligible and needs to be taken into account, usually by performing additional experiments. Thus, there is an increasing effort towards enabling simultaneous TEM probing and characterization with complementary techniques. Thanks to the strongly enhanced electric fields generated around metallic nanoantennas, LSPR-based sensing is a proven tool to study processes at the nanoscale [2], and an ideal complement to TEM since it probes a much larger volume of the specimen.

We have fabricated a TEM specimen holder hosting a miniaturized optical bench [3] that allows for sample illumination and spectroscopic readout. Specimens can be heated up to 1300 ºC, and the holder is compatible with differentially pumped environmental TEM (ETEM), with no prior modification to the microscope required. Comparison between signals obtained simultaneously by TEM and LSPR provides indication of the relevance of electron beam-induced effects. Moreover, we enable for the first time direct correlation of the LSPR response with changes in physical properties of the specimen. We investigate thermally-induced sintering of metal nanoparticles, a crucial process in deactivation of catalysts [4]. We envision the combination of LSPR sensing with probing by ETEM to become a versatile tool to study processes at the nanoscale, especially taking place on (photo)catalysts.

References:

[1] J.-M. Herrmann Top. Catal., vol. 34, no. 1–4, pp. 49–65, May 2005.

[2] E. M. Larsson, C. Langhammer, I. Zorić, and B. Kasemo, Science, vol. 326, no. 5956, pp. 1091–4, Nov. 2009.

[3] F. Cavalca, A. B. Laursen, B. E. Kardynal, R. E. Dunin-Borkowski, S. Dahl, J. B. Wagner, and T. W. Hansen Nanotechnology, vol. 23, no. 7, 075705, Feb. 2012.

[4] C. H. Bartholomew, Appl. Cat. A, vol.  212, no. 1–2, pp. 17–60, Apr. 2001.

Acknowledgments: The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA Grant Agreement No. 609405 (COFUNDPostdocDTU).

Figures:

Top left: low magnification scanning electron micrograph of a microelectromechanical systems based chip for specimen support and heating experiments (scale bar: 100 µm). Top right: transmission electron micrograph of an electron transparent ‘window’ (scale bar: 500 nm). Au nanodisks used for plasmonic sensing can be distinguished on the surface of the window. Bottom right: normalized optical spectra acquired using the novel TEM specimen holder for one type of heating chip with Au sensors (solid line), the same type of heating chip without Au sensors (broken line) and for another type of chip without Au sensors (dotted line).

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