Precise measurement of the electron beam current in a TEM

Area of Science:

• Materials Science
• Physics
• Electron Microscopy

Background:

• Quantitative transmission electron microscopy (TEM) methods, like the ζ-factor technique, demand accurate electron beam current measurements.
• Existing methods for measuring electron beam current in TEM often suffer from inaccuracies, particularly at low current levels.

Purpose of the Study:

• To design and validate a macroscopic Faraday cup for precise electron beam current measurement in TEM.
• To assess and compare the accuracy of various electron beam current measurement techniques.

Main Methods:

• Development and implementation of a macroscopic Faraday cup that replaces the TEM viewing screen.
• Comparison of Faraday cup measurements with built-in TEM screen amperimeters, spectrometer drift tubes, ultrafast electron detection cameras, and electron counting techniques.
• Investigation and reformulation of the electron counting technique for improved accuracy at low currents (<5pA).

Main Results:

• The developed Faraday cup provides highly accurate electron beam current measurements, limited only by the amperemeter precision, suitable for currents >5pA.
• Built-in TEM screen amperimeters and general screen measurements tend to underestimate the electron beam current.
• Refined electron counting techniques demonstrate accurate high-precision measurements for currents <5pA.

Conclusions:

• The macroscopic Faraday cup is an affordable, easy-to-install, and highly accurate device for measuring electron beam currents in TEM.
• The study highlights significant inaccuracies in common TEM current measurement methods, necessitating improved techniques.
• Optimized electron counting offers a viable solution for precise low-current measurements in scanning transmission electron microscopy (STEM).