Precise evaluation of specimen thickness by convergent-beam electron diffraction technique and electron energy-loss spectroscopy

To determine the mean free path (λ_p) for inelastic electron scattering of a silicon crystal at an accelerating voltage of 200 kV precise measurements of the specimen thickness were carried out by convergent-beam electron diffraction (CBED) technique and electron energy-loss spectroscopy (EELS) using an analytical electron microscope. Through the evaluation of the specimen thickness by using CBED technique, it was found that precise measurements in the case of 400 reflection with convergent beam angle of 12 mrad were performed in the condition that the specimen thickness was set to be in the range of 100 to 500 nm. By subtracting the background in CBED patterns with an energy filter, minima and maxima of the intensity profile of the symmetric fringes in the diffraction disks were clearly observed. Consequently, it was clarified that the maximum thickness measurable for the 400 diffraction disks increased from 400 nm to 670 nm. Using the precise specimen thickness evaluated by CBED technique, λ_p with the collection semiangle 157 mrad was determined to be about 147±5 nm through EELS.