A simple calibration for routine section thickness measurements using current density ratios

A method to calibrate current density ratios for the determination of specimen thickness is presented. This method uses a tilt series from a single noncrystalline specimen to create different thicknesses; these are used to generate data points to establish the relationship between specimen thickness and current density ratio. The actual specimen thickness at 0° tilt was determined to an accuracy of 5 nm by a parallax method. From the calibration curves obtained, we observed that the current density ratio was sensitive to relative thickness changes on the same section of less than 1 nm when a 50‐μm objective aperture was used.