MS-1-P-5771 Application of EFTEM and EELS for investigations of electronic and structural properties of nanostructures

Transmission electron microscope offer wide range of measurement possibilities like high efficient electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM)[1]. That allows, among others, the measurement of surface plasmons resonance (SPR) and in the case of structures with the size below tens nanometers – Localized Surface Plasmons Resonance (LSPR)[2].
The phenomena of electron energy loss can be exploited in both scanning and imaging working mode of TEM. In the scanning mode a spectrum is recorded at a given beam position and therefore the spatial resolution is determined by beam size and specimen thickness, which indicate a volume from which the spectrum is collected. The energy resolution depends on monochromaticity of the incident electron beam and the quality of a spectrometer. Nowadays  the energy resolution of monochromator is 0,2 eV at a 300 keV and about 0,15 eV at a 80 keV. STEM mode connection with such a good energy resolution allows the measurement of the plasmon resonance eve n in nanostructures with dimensions less than 5 nm.
EFTEM technique is to form an image with electrons within a certain kinetic energy range. The EFTEM standard procedure for elemental mapping is based on recording three images: two pre-edge images with electron energy loss window before an absorption edge and one post-edge image with energy window after the absorption edge. The element mapping is obtained by the post-edge image after removing a background extrapolated from two pre-edge images. The intensity of the resulting image is proportional to the concentration of the element for which the absorption edge was used. Fig. 1 and 2 shows the application of the EFTEM elements mapping procedure in the case of AlN/GaN heterostructure.
EFTEM is very useful method to mapping of the distribution of elements in the investigating sample. Fig.3 and 4. present maps obtained by EFTEM method for Ag nanoparticles. An interesting application of EFTEM is mapping of electronic properties with a use of plasmon absorption [3]. It is well known that plasmon excitation energy depends on the mobility and density of charge carriers. The energy of plasmon’s peak is correlated with local structure and therefore gives information about relation between electronic properties and structural defects.


[1] F.J. Garcia de Abajo. Optical excitations in electron microscopy Rev. Mod. Phys. 2010;82:209-275
[2] JA. Scholl, AL. Koh, JA. Dionne. Quantum plasmon resonances of  individual metallic nanoparticles Nature 2012;483:421-428
[3] J. Nelayah, M. Kociak, O. Stephan, FJG. de Abajo, M. Tence, L. Henrard, D. Taverna, I. Pastoriza-Santos, LM. Liz-Marzan, Ch. Colliex. Mapping surface plasmons on a single metallic nanoparticle. Nature Physics 2007;3:348-353