Design and evaluation of a novel Faraday cup for easy and accurate beam current measurement in a transmission electron microscope.

Abstract

Beam current measurement is a crucial step in estimating the electron dose when studying beam-sensitive samples in electron microscopy. A Faraday cup is a standard tool for measuring beam current; however, commercially available Faraday cups for transmission electron microscopes (TEM) are limited, expensive, and often difficult to use as the cup itself is invisible in the TEM. We herein present a new Faraday cup design that fits into an insulated TEM holder of Hitachi HT7700 and HT7800 series and can be easily located using four symmetrical through holes around the cup. This design also accommodates the 3 mm TEM mesh grid in the holder and allows both sample imaging and access to the Faraday cup within the TEM stage movement range. We evaluated the effectiveness of our Faraday cup in capturing the electron beam by varying the diameter to depth ratio and material of the Faraday cup through experimental measurements and Monte Carlo simulations, demonstrating an accuracy better than 1-2 %. The preferred configuration is an aluminum cup with a diameter of 0.2 mm and a depth of 0.8 mm. Monte Carlo simulations also suggest that this Faraday cup provides accurate beam current measurement at different electron energies. Our novel Faraday cup design provides a practical, simple, and cost-effective solution for beam current measurement in a TEM.