title: Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS.
abstract: This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250nm. The effect of collection semi-angle (β) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3mrad that is about 2x convergence semi-angle (9.0mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different β angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis.
authors.affiliation: School of Materials Science and Engineering, Central South University, Changsha 410083, China.
authors.forename: B Q
authors.initials: BQ
authors.lastname: Wei
authors.affiliation: Advanced Research Centre, Central South University, Changsha 410083, China.
authors.forename: N
authors.initials: N
authors.lastname: Yan
authors.affiliation: School of Materials Science and Engineering, Central South University, Changsha 410083, China.
authors.forename: J X
authors.initials: JX
authors.lastname: Gao
authors.affiliation: School of Materials Science and Engineering, Central South University, Changsha 410083, China.
authors.forename: D D
authors.initials: DD
authors.lastname: Li
authors.affiliation: Advanced Research Centre, Central South University, Changsha 410083, China.
authors.forename: Z G
authors.initials: ZG
authors.lastname: Shang
authors.affiliation: School of Materials Science and Engineering, Central South University, Changsha 410083, China; Advanced Research Centre, Central South University, Changsha 410083, China. Electronic address: cbbr16@126.com.
authors.forename: K
authors.initials: K
authors.lastname: He
keywords: Collection semi-angle; Graphite spheroid; Optical property; Refractive index; STEM-EELS; Thickness measurement