Continued skirmishing on the wave-particle frontier

Highlights: • Waves and particles in electron microscopy. • Updating Richard Feynman. • Johnson noise stimulation of bremmstrahlung. -- Abstract: Historical developments in electron microscopy where understanding lies at the interface between the particle and wave pictures of the electron are reviewed. Electron optics has remained mainly particle-based but imaging is now substantially dependent on wave methods which are now pushing it to new heights. Spectroscopy in the low loss region has used Fermi's classical electron model which can also describe the main effects of Johnson noise. It is confirmed that the RMS Johnson noise scattering of an aloof beam electron is proportional to its wavelength and to the square root of the temperature. If the conductivity σ is high, it is independent of σ. In the performance of magnetic spectrometers, the angular deflections due to the walls may be less significant than that generated in the slits. The angular deflections due to the many bremmstrahlung events in the spectrometer seem to be negligible but the influence of Johnson noise on them is beyond the scope of the classical Fermi theory and will need to be addressed by the quantum mechanical spontaneous wave theory.