TKD in the SEM is applied to a thin foil at least parts of which have to be transparent to electrons. 1c) a dedicated detector with the transparent phosphor screen is placed concentrically to the primary beam spot beneath the sample. In TKD the detector comes in from the side beneath the horizontal sample.Įither the standard EBSD detector (Fig. The cone sections of the acquired patterns are marked in green.įig. The height of the EBSD detector is therefore set such that the intensity maximum falls on the center of the phosphor screen.įigure 1 Kikuchi diffraction in the SEM. The maximum is close to the direction of optical reflection that a light beam would have from an opaque surface. As a consequence of strong forward scattering of energetic electronsīy matter a steep lobe of intensity is generated. The distance between sample and screen is typically 2 cm, roughly like the diameter of the screen, so that a wide cone of about 45º of backscattered electrons is acquired. The EBSD detector is placed horizontally on the side (Fig. In BKD mode the sample surface is steeply inclined by about 60º to 70º out of the horizontal to produce a sufficient backscatter intensity. For automated mapping a computer controlled scan of the beam spot is implemented.
These requirements limit TKD orientation mapping to the use of a TEM with a condenser objective lens and microbeam diffraction facility such as for instance the Philips CM series, respectively FEI TEM. Should cover a large angular range and be undistorted. Pattern intensity is of minor concern in TKD with a TEM. A circular continuous density filter in the optical path is of advantage to equalize the steep drop of intensity from the blooming primary beam spot to the dim marginal area. In the TEM the diffraction patterns are either acquired with a CCD camera placed on-axis at the bottom of the microscope column or with a retractable CCD camera on the side-entry flange above the viewing screen. Recently interest in TKD has risen again, in particular as a supplementary facility to an EBSD system, a wishful dream of improving resolution in texture analysis. Since the end of last century Backscatter Kikuchi Diffraction (BKD) in the SEM, then named Electronīackscatter Diffraction (EBSD), is about to prevail thanks to the availability of commercial systems, the ease of operation and sample preparation, and enabling of dynamic experiments. 475.Įxperimental work has been focused during the first decades preferably on Transmission Kikuchi Diffraction (TKD) because of technical limitations.
Imperial Academy of Japan (Tokyo) 4 (1928) pp. The first Transmission as well as Backscatter Kikuchi Patterns (later named TKP resp. BKP) were published in the same volume of Proc.
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