Increasing the beam current to improve the signal-to-noise ratio (SNR)  increases the probe size, which deteriorates the spatial resolution. The spatial resolution achieved using a compromise for these parameters combined with averaging of repeated line scans from the same sample was estimated to be ≤ 0.5 nm.
Spectroscopy can be done with either TEM imaging mode or TEM diffraction mode
(recommended). Imaging mode gives better energy resolution while diffraction mode
gives better spatial resolution.
Use small camera length (0.20 m) to get better signal-to-noise ratio.
The recorded electrons in the zero loss peak have passed the sample without energy loss or with energy changes too small to be measurable from phonon excitations (a few 10 meV).
 Heiko Stegmann and Ehrenfried Zschech, Compositional analysis of ultrathin silicon oxynitride gate dielectrics by quantitative electron energy loss spectroscopy, Applied Physics Letters, 83 (24), (2003) 5017.