Typical dark-field STEM images of as-prepared trifluoromethionine (Tfm) and methionine (Met) powder clusters are shown in Figs. and, respectively, with corresponding EELS recorded aloof from the edge of the particles also shown in the same figure. The position of the electron probe is indicated in the survey images at fixed distances from the surface (~50 nm and ~30 nm, for Tfm and Met, respectively). At the beam positions used, no radiation damage of the sample was observed . A peak in the EELS data is present at an energy-loss of ~139 meV (~1121 cm -1 ). This is present in the spectra for Tfm but is absent in those for Met. Similar spectral features are also present in the FTIR spectra collected from the same powder samples, shown for comparison in the same figure. The FTIR spectrum of Tfm also exhibits a sharp peak at ~136 meV (~1097 cm - 1 ) with a weak shoulder at ~146 meV (~1177 cm -1 ) but there are no substantial differences between the vibrational frequencies collected by FTIR, and EELS, from either sample. The slight off-set of momentum and light transfer modes are visualized and likely due to the surface vs bulk interaction that occurs in EELS and FTIR respectively . To compare the EELS data with the as-acquired FTIR spectra, which has a higher energy resolution of ~1 meV, the FTIR spectra were broadened with a Gaussian kernel having standard deviation, σ of 4 meV, corresponding to a full width at half maximum (FWHM) of 2.35 σ (see Supporting Information). The final energy broadening of ~9 meV of the FTIR data is consistent with the energy resolution measured from the FWHM of the experimental EELS zero-loss peak and after broadening, the dominant frequency in the Tfm FTIR spectrum appears as a single peak at ~136 meV, in agreement with the EELS data. The highest intensity feature in the Tfm spectrum is attributed to a stretching mode of the C-F bond, which was validated by the DFT calculations. This assignment supports our hypothesis that the EEL spectra can selectively measure the vibrational signature of the C-F bond in the trifluoromethyl (CF3) functional group of Tfm. Furthermore, the EELS data also records the features of the raw and broadened FTIR spectra, which can be attributed to all the major vibrational modes in Met (Table ). The vibrational signatures of the carbonyl (C=O) group stretching mode and the scissoring motion of the amine (NH2) group contribute to the most intense spectral features at ~190 meV. The observation of the carbonyl frequency at a reduced energy relative to the typical values for carboxylic acids suggests that the molecules are present in a zwitterionic form within the powder . At lower energy, the broader peak at ~170 meV is attributed to a conglomerate of various C-H bending modes. At higher energy-loss, the peak at ~360 meV is assigned to stretching modes of the hydroxyl (O-H) and amine (N-H) groups. A shoulder feature at around 320 meV is also associated with various C-H stretching modes. This peak is weaker in L-trifluoromethionine due to the absence of the methyl group. The peak at 293 meV (2365 cm -1 ) in the raw FTIR data is a known instrument feature corresponding to the C=O stretch of environmental CO2, which is absent in the EELS data, which are recorded in vacuum. Finally, the distance from the sample edge approximately defines the lateral spatial sensitivity of the EELS data which is of the order of few tens of nanometers. This sensitivity is superior to that of conventional FTIR which records the vibrational response from a much larger ensemble of microcrystallites.