Depth resolution in on-axis TKD 1105
requires first the production of a diffuse background by incoherent scattering, from which only a small part produces Kikuchi diffraction according to the small relative intensity in patterns of Kikuchi diffraction in comparison with the background intensity. With overall much less intensity, the Kikuchi diffraction would requiremuch less crystal thickness to drop, by absorption, below the signal/noise ratio of the camera in comparison to spots.
CONCLUSION
The depth resolution of the on-axis TKD technique in SEM was investigated with a specifically designed and produced twinned cubic silicon bi-crystal. The main conclusions are the following:
∙ The existence of a depth resolution for TKD can be explained as follows: unlike Bragg diffraction, Kikuchi diffraction beneficiates from emitting sources distributed inside the sample. Hence, each layer of the sample generates independently Kikuchi diffraction. However, the Kikuchi diffraction produced by a layer found at a given depth suffers an absorption on its way out, as a function of the thickness that remains to be crossed. Inevitably thismakes the last layers the most visible. Then, because the hardware and software limitations necessarily produce a detection threshold, only the contribution from a finite fraction of these layers, at the bottom, is effectively detected, giving rise to what we call a depth resolution as a finite length, although the absorption responsible for this depth resolution remains essentially a continuous phenomenon. In that sense, a finite depth resolution value is necessarily highly relative and is not an intrinsic property.
∙ The depth resolution, defined here as the minimal thickness of material at the bottom of the sample such that the material above does not produce a contribution to the Kikuchi diffraction pattern that can be detected to the naked eye, was measured on cubic silicon by on-axis TKD, and ranges from 30 to 65nm in the range 10–30 keV, with a close to linear dependence with incident energy, while there is no dependence with the total sample thickness. It means that the depth resolution and lateral resolution vary in opposite ways with incident energy.
∙ The observed linear dependence of the depth resolution with incident energy is the consequence of the mean free paths for phonon, plasmon, and elastic scattering having a linear dependence with energy. In this situation, a fixed number of interactions is responsible for the depth resolution measured. More precisely, the depth resolution measured on silicon corresponds to 1.5 and 2.6 times the plasmon and elastic mean free path, respectively, although it is not currently clear which scattering process in particular, plasmon, phonon, or elastic, is responsible for the absorption at the origin of the depth resolution.
∙ Alternatively, a simple relationship might provide a rapid evaluation of the depth resolution of on-axis TKD for any incident energy and atomic number from the mean
absorption coefficient µ0. The depth resolution would be given by 2.6/µ0 (E, Z, T). If the dependence of the depth resolution with incident energy can be accounted for by this relationship, the dependence with atomic number remains to be confirmed.
∙ The absorption producing the depth resolution, making grains less and less visible away from the back surface of the lamella, most likely varies with the exponential of the thickness crossed. In addition to the absorption, a second mechanism was evidenced: the progressive generation of Kikuchi diffraction with increasing grain size. Hence, the contribution of a grain to the Kikuchi pattern depends not only on its position inside the depth resolution layer, but also on its size, meaning that the grains right at the back surface will not always necessarily be the ones contributing most to the Kikuchi pattern. Thus, to better interpret patterns, the generation of Kikuchi diffraction with thickness should also be studied.
ACKNOWLEDGMENTS
This work was supported by the French State through the program“Investment in the future” operated by the National Research Agency (ANR) and referenced by ANR-11- LABX-0008-01 (LabEx DAMAS).
REFERENCES
BHATTACHARYYA,A.&EADES, J.A. (2009). Use of an energy filter to improve the spatial resolution of electron backscatter diffraction. Scanning 31, 114–121.
BRODU, E., BOUZY,E. & FUNDENBERGER, J.-J. (2017). Diffraction contrast dependence on sample thickness and incident energy in on-axis Transmission Kikuchi Diffraction in SEM. Ultramicroscopy 181, 123–133.
BRODU, E., BOUZY, E., FUNDENBERGER, J.-J., GUYON, J., GUITTON,A. & ZHANG, Y. (2017). On-axis TKD for orientation mapping of nanocrystalline materials in SEM. Mater Charact 130,92–96.
BRODUSCH, N., DEMERS,H. & GAUVIN, R. (2013). Nanometres- resolution Kikuchi patterns from materials science specimens with transmission electron forward scatter diffraction in the scanning electron microscope. J Microsc 250,1–14.
CREWE, A.V., WALL,J.&LANGMORE, J. (1970). Visibility of single atoms. Science 168, 1338–1340.
DEAL, A., HOOGHAN,T. & EADES, A. (2008). Energy-filtered electron backscatter diffraction. Ultramicroscopy 108, 116–125.
DINGLEY,D. (2004). Progressive steps in the development of electron backscatter diffraction and orientation imaging microscopy. J Micros 213, 214–224.
DROUIN,D., COUTURE,A.R., JOLY,D., TASTET,X.,AIMEZ,V.&GAUVIN,R. (2007). CASINO V2.42 – A fast and easy-to-usemodeling tool for scanning electron microscopy and microanalysis users. Scanning 29,92–101.
FUNDENBERGER, J.J., BOUZY, E., GORAN, D., GUYON, J., YUAN,H. & MORAWIEC, A. (2016). Orientation mapping by transmission- SEM with an on-axis detector. Ultramicroscopy 161,17–22.
FUNDENBERGER, J.-J.,MORAWIEC, A., BOUZY,E.&LECOMTE, J.-S. (2003). Polycrystal orientation maps from TEM. Ultramicroscopy 96, 127–137.
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