A SIMPLE CALIBRATION FOR ROUTINE SECTION THICKNESS MEASUREMENTS USINGCURRENT-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 betwee n specimen thickness and current density ratio. The actual specimen th ickness at O degrees tilt was determined to an accuracy of 5 nm by a p arallax 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-mu m objective apertu re was used.