T-SEM EDS and TKD Combined for Elemental and Crystallographic Analysis.

To understand the behavior of any nanostructure, analysis of the chemical composition and its arrangement on the nanoscale is vital. We demonstrate the combination of energy-dispersive X-ray spectroscopy (EDS) and transmission Kikuchi diffraction (TKD) in SEM for studying the elemental composition and crystallographic properties of solar cell materials prepared as FIB lamellae. We show that achieving useful results at nanometer scale in a suitable amount of time in SEM, not STEM, is possible by combining on-axis TKD [1] with an annular EDS detector [2] and specimen preparation by FIB. The results are quantitative element maps and line profiles combined with crystal phase and orientation distribution in the absorber and buffer layers of CIGS solar cells investigated in SEM.<br/>The annular EDS detector is placed horizontally between the specimen and the pole piece achieving a solid angle for X-ray collection of about 1 steradian enabling high count rates also in case of low X-ray yield, for example from thin lamellae, light elements and during fast scanning of beam sensitive and/or large specimens. The annular arrangement of the active SDD quadrants parallel to the specimen surface around a central aperture to pass the electron beam enables a high take-off angle as well, minimizes absorption effects and allows the analysis of rough topography or bent specimens. This geometry is easily combined with diffraction pattern acquisition using a detector directly underneath the specimen.<br/>Quantitative EDS of electron transparent lamellae can deliver element distribution and even the specimen thickness, the latter if applying the EDS Zeta-factor method [3]. Crystallographic grain phase, size and orientation are accessible via TKD. The combination of crystallographic and chemical information on the nanoscale via TKD and EDS is particularly promising for correct quantitative analysis. Small grains can lie in front of each other and produce mixed diffraction patterns. Therefore, to interpret grain size and orientation from TKD correctly, the lamella thickness must be known. Lamella thickness can be determined using sample tilt in the FIB which also enables calibrating the Zeta-factors for successful quantitative chemical analysis.<br/>[ 1] Brodu E, Bouzy E and Fundenberger: J 2017 <i>Microsc. </i><i>Microanal.</i> <b>23 </b>(Suppl. 1) 530-531.<br/>[ 2] Terborg R and Rohde M: <i>EMC 2008 14th European Microscopy Congress</i>. (Luysberg M, Tillmann K and Weirich T; Eds.) 1-5 September 2008, Aachen, Germany. (Berlin, Heidelberg: Springer). https://doi.org/10.1007/978-3-540-85156-1_317.<br/>[ 3] Watanabe M and Williams D B: 2006 <i>J. Microscopy</i> <b>221 </b>89-109.