two, while somewhat ill-defined, is in the vicinity of 50 eV energy loss. Instrumental developments have opened up the ultra-low energy loss part of the EELS spectrum, enabling vibrational spectroscopy in the TEM. Both IR-active and non-IR-active vibrational modes are present in EELS. EEL spectrum The electron energy loss (EEL) spectrum can be roughly split into two different regions: the low-loss spectrum (up until about 50eV in energy loss) and the high-loss spectrum. The low-loss spectrum contains the zero-loss peak as well as the plasmon peaks, and contains information about the band structure and dielectric properties of the sample. The high-loss spectrum contains the ionisation edges that arise due to inner shell ionisations in the sample. These are characteristic to the species present in the sample, and as such can be used to obtain accurate information about the chemistry of a sample. Thickness measurements EELS allows quick and reliable measurement of local thickness in transmission electron microscopy. The most efficient procedure is the following: Measure the energy loss spectrum in the energy range about −5..200 eV (wider better). Such measurement is quick (milliseconds) and thus can be applied to materials normally unstable under electron beams. Analyse the spectrum: (i) extract zero-loss peak (ZLP) using standard routines; (ii) calculate integrals under the ZLP (I0) and under the whole spectrum (I). The thickness t is calculated as mfp*ln(I/I0). Here mfp is the mean free path of electron inelastic scattering, which has been tabulated for most elemental solids and oxides. The spatial resolution of this procedure is limited by the plasmon localization and is about 1 nm, meaning that spatial thickness maps can be measured in scanning transmission electron microscopy with ~1 nm resolution. Pressure measurements The intensity and position of low-energy EELS peaks are affected by pressure. This fact allows mapping local pressure with ~1 nm spatial resolution. Peak shift method is reliable and straightforward. The peak position is calibrated by independent (usually optical) measurement using a diamond anvil cell. However, the spectral resolution of most EEL spectrometers (0.3-2 eV, typically 1 eV) is often too crude for the small pressure-induced shifts. Therefore, the sensitivity and accuracy of this method is relatively poor. Nevertheless, pressures as small as 0.2 GPa inside helium bubbles in aluminum have been measured. Peak intensity method relies on pressure-induced change in the intensity of dipole-forbidden transitions. Because this intensity is zero for zero pressure the method is