Electron spectrometer calibration method

An energy dispersion calibration method for calibrating an electron spectrometer of an electron spectrometer system including at least one electron emission source, electron optics and the electron spectrometer, the electron spectrometer system being configured to produce an electron energy spectrum electrons received by the electron spectrometer, the election energy spectrum including a plurality of channels defining an electron energy range the electron energy spectrum, the method comprising:

• providing an optical resonator configured to exchange energy with the electrons of the electron spectrometer system;
• obtaining, using the electron spectrometer, at least one electron energy loss spectrum produced by electrons of the electron spectrometer system exchanging energy with at least one resonant optical mode of the optical resonator into which light at a resonant wavelength is coupled;
• calculating a Fourier transform of the at least one electron energy loss spectrum or a part of the at least one electron energy loss spectrum;
• determining an energy dispersion ΔE of the electron spectrometer according to the equation
• Δ
• ⁢
• E
• =
• f
• E
• ⁢
• hc
• λ
• ⁢
• N
• ⁢
• or
• ⁢
• Δ
• ⁢
• E
• =
• f
• E
• ⁢
• E
• p
• N
• where λ is the resonant wavelength of the light coupled into the optical resonator, h is Planck's constant, c is the speed of light in vacuum, Ep is the resonant photon energy of the light coupled into the optical resonator, N is the number of channels or data points along an energy axis of the at least one electron energy loss spectrum used in determining the Fourier transform of the at least one electron energy loss spectrum or a part thereof, and fE is the number of reciprocal energy space data points or coordinates between (i) a DC spectral component peak of the Fourier transform of the at least one electron energy loss spectrum or a part thereof and (ii) a sideband peak or a center of a sideband peak of the Fourier transform (FT) of the at least one electron energy loss spectrum or a part thereof, the sideband peak originating from electron energy exchange with the at least one resonant optical mode of the optical resonator, the determined energy dispersion ΔE defining an incremental energy value of the plurality of channels defining the election energy range of the election energy spectrum or an incremental energy value of a subset of the plurality of channels used to calculate the Fourier transform of the part of the at least one electron energy loss spectrum;
• and
• using the determined energy dispersion ΔE to provide calibrated electron energy spectrum when the electron spectrometer system is used to perform electron spectroscopy.