Electron energy loss spectroscopy (EELS) measures the spectral distribution of energy transferred from an incident electron beam into a specimen. In general, there are mainly two types of fundamental methods:
i) Low energy beams reflected by solid surfaces, presenting the excitation spectrum from meV to eV. A representative technique is vibrational spectroscopy.
ii) High energy beams transmitted through thin TEM films, presenting the inelastic scattering events in an energy range of eV to keV.
Electron monochromator  has improved the EELS energy resolution about 3-fold, to ~10 meV. At such high energy resolution, vibrational spectroscopy is available in the electron microscope . As shown in the vibrational spectrum in Figure 2398, the different peaks can be assigned to different types of bonds and vibration modes.
|Figure 2398.UHR (ultra-high energy resolution) EEL spectrum of guanine
(Nion UltraSTEM100MC, 60 kV). 
O. L. Krivanek et al., Microscopy 62 (2013) 3-21.
 O. L. Krivanek et al., Nature 514 (2014) 209-212.
 H. Cohen, P. Rez, T. Aoki, P.A. Crozier, N. Dellby, Z. Dellby, D. Gur, T.C. Lovejoy, K. March, M.C. Sarahan, S.G. Wolf and O. L. Krivanek, Hydrogen Analysis by Ultra-High Energy Resolution EELS, Microsc. Microanal. 21, 661, 2015.