Practical Electron Microscopy and Database

In practice, experimental EELS profiles at interfaces between two thin films are not abrupt. The broadening of the EELS profiles at the interfaces normally is rather due to the thickness of the STEM specimen and to the probe broadening than due to the formation and/or inter–diffusion of chemical compounds.

As mentioned in page4487, the spatial resolution of STEM measurements is determined by the specimen thickness, due to cone shape of the probe. For instance, if we have the experimental conditions below:
        i) A specimen is in thickness of 600 nm.
        ii) The incident electron spot size is ~1 nm.
        iii) The convergence angle of the incident electron is 10 mrad.
Then, the diameter of the electron at the bottom surface of the specimen is about 10 nm. Therefore, the spatial resolution will be about 10 nm in diameter.