LabAdviser/314/Microscopy 314-307/SEM/Nova/Transmission Kikuchi diffraction: Difference between revisions

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 = On-axis Transmission Kikuchi diffraction =
-A development of the EBSD technique, proposed in 2012, led to a signi
+This technique was introduced by Keller and Geiss in 2012 and is based on the collection of Kikuchi patterns from electron transparent samples. For TKD an electron transparent sample is required, resulting in an intensive sample preparation. This also results in both a smaller region being available for analysis and additional stress release considerations, as there are two free surfaces rather than one. Furthermore the acquisition of TKD patterns from relatively thick samples can be done (as soon as they are electron transparent at that thickness), but the effects of beam broadening due to electron scattering inside the sample become stronger in increasingly thick specimens and lead to degradation of the lateral spatial resolution.
-�cant improvement in spatial resolution. The new technique, introduced
-by Keller and Geiss [40], is based on the collection of Kikuchi patterns from
-electron transparent samples using a conventional EBSD detector. In the
-new geometry the sample, to improve the detector electron collection ef-
-�ciency, is tilted away from the EBSD detector by 20°. In this way, the
-collected di�raction pattern is projected from the lower surface of the sample.
-This technique has been given the name transmission EBSD (t-EBSD)
-at �rst [41]. However, in this case the term electron backscatter di�raction is
-inaccurate, because the collected di�racted electrons are not backscattered,
-but transmitted through the sample instead. In order to deal with that, a
-more appropriate name, transmission Kikuchi di�raction (TKD), has been
-introduced in later publications
-This mechanism leads to two main e�ects: (1) for TKD an electron
+In 2016 the on-axis TKD configuration was presented. In this system the detector is located perpendicularly beneath the electron transparent sample on the optical axis of
-transparent sample is required, resulting in more intensive sample preparation
+the microscope, obtaining an instrument resolution almost the same as that using Kikuchi patterns in TEM. A schematic illustration of the detector is shown in Fig. 3.8.
-compared to EBSD. This also results in both a smaller region being
-available for analysis and additional stress release considerations, as there
-are two free surfaces rather than one; (2) the acquisition of TKD patterns
-from relatively thick samples can be done (as soon as they are electron
-transparent at that thickness), but the e�ects of beam broadening due to
-electron scattering inside the sample become stronger in increasingly thick
-specimens and lead to degradation of the lateral spatial resolution.
+Moving the detector from a high-angle to the on-axis position permits to reduce the probe current and size to record a solvable pattern. Kikuchi patterns are more intense at small scattering angles (i.e., near the direction of the optical axis) than at higher angles. Therefore, the intensity of the incident electron beam, and thus the probe size needed to record a solvable pattern is smaller when the detector is moved from a high-angle to the on-axis position. The probe size in combination with the beam broadening affect the total interaction volume, and the width of the interaction volume is directly linked to the lateral resolution. All the experiments and results presented in the next section were obtained using the on-axis detector configuration, which has already become the standard geometry for TKD measurements.
-The last step in the evolution of TKD has been carried out by Fundenberger,
-together with Bruker Nano, in 2016 [46]. They presented a new
-con�guration for the SEM-based mapping with the detector located perepndicularly
-beneath the electron transparent sample on the optical axis of
-the microscope, obtaining an instrument resolution almost the same as that
-using Kikuchi patterns in TEM. A schematic illustration of the detector is
-shown in Fig. 3.8.
-Moving the detector from a high-angle to the on-axis position permits
-to reduce the probe current and size to record a solvable pattern. Kikuchi
-patterns are more intense at small scattering angles (i.e., near the direction
-of the optical axis) than at higher angles. Therefore, the intensity of the
-incident electron beam, and thus the probe size needed to record a solvable
-pattern is smaller when the detector is moved from a high-angle to the onaxis
-position. The probe size in combination with the beam broadening
-a�ect the total interaction volume, and the width of the interaction volume
-is directly linked to the lateral resolution. Further information about TKD
-can be found in the detailed review presented by Sneddon [47]. All the
-experiments and results presented in the next section were obtained using
-the on-axis detector con�guration, which has already become the standard
-geometry for TKD measurements.
 = In-situ heating TKD analysis of ultra-thin metal fi�lms =