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ECP

ECP: Electron Channeling Pattern
Definition:A type of diffraction pattern obtained in a scanning electron microscope (→SEM) by rocking the beam over a pivot point and recording the backscatter electron intensity.
Explanation:As explained in the section on electron channeling contrast imaging(→ECCI), the backscatter electron intensity recorded in a →SEM depends on the crystallographic direction along which the electron beam penetrates into a sample. During rocking the primary electron beam over a pivot point on the sample and plotting the recorded intensity over the rocking angle, one may display this orientation dependence in form of a characteristic pattern, a so-called ECP. This pattern has the same geometry as a Kikuchi diffraction pattern (or an electron backscatter diffraction (→EBSD) pattern) and consists of bright bands bounded by dark lines. The dark lines correspond to so-called channeling conditions, where particularly few electrons are backscattered. These conditions are used in ECCI to observe lattice defects.

When a sample is tilted, the observed ECP moves over the screen. This can be used to set channeling conditions for the subsequent imaging: the conditions at the centre of the ECP determine the channeling conditions during normal imaging.

ECP has been used in former times to determine crystal orientations and crystallographic phases. However, most modern microscopes do not allow to obtain large rocking angles. Furthermore, the spatial resolution of the ECP technique is rather bad (in the order of 5 µm). Therefore, most applications of ECP have been replaced by EBSD. However, ECP may still be very useful to obtain exact channeling conditions for ECCI.
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Diagram:

Typical electron channeling pattern from copper at 40 kV.
SFB-Link:Electron channeling patterns are used indirectly for cECCI; after measurement of crystal orientations by EBSD, a computer program is used to simulate ECPs and allow positioning of a crystal into channeling conditions.