1. Kikuchi patterns are produced when inelastically scattered electrons in a specimen undergo Bragg reflections, forming pairs of excess and defect lines called Kikuchi lines. 2. When crystal planes are inclined against the electron beam, the lines have different intensities - defect lines near the beam and excess lines far from it. 3. As the plane orientation approaches symmetry, the lines transform into asymmetric Kikuchi bands with higher intensity between the reflection positions.

1. FORMATION OF KIKUCHI
PATTERNS IN SEM AND TEM
GERUGANTI SUDHAKAR
PHD(MATERIALS ENGINEERING)

8. The incident electron beam is directed to the point of interest
(POI) on the sample surface and thus, the elastic scattering of
the electron beam induces the electrons to diverge from a
point just below the sample surface and to impinge on crystal
planes in all directions. Backscattered electrons that
satisfy Bragg's law for a given plane generate two diffraction
cones from the front and back surfaces of the plane. These
cones are produced for each family of lattice planes. When
these cones intersect the phosphor screen or camera thin
bands are formed. These bands are called Kikuchi lines. The
Kikuchi lines appear as almost straight lines because the cones
are very shallow due to the small Bragg angle (order 1°) with a
very small electron wavelength. EBSD software can
automatically analyze the individual Kikuchi lines by comparing
them with the theoretical Kikuchi lines in database.

14. •Kikuchi pattern
1.The Kikuchi pattern is a diffraction pattern produced by Bragg reflections of inelastically scattered
(thermal diffuse scattering) electrons in a specimen.
2. Since the inelastically scattered electrons distribute over large angles, the Bragg reflections by the
inelastically scattered electrons do not form diffraction spots but form a pair of excess and
defect lines (Kikuchi lines) respectively by hkl and -h-k-l reflections.
3. The low-intensity (defect) Kikuchi lines appear near side of the direction of the incident beam,
whereas the high-intensity (excess) Kikuchi lines appear far side of the direction.
4. When low-order reflections hkl and -h-k-l are strongly excited, a high-intensity (excess) band
(Kikuchi band) is formed between the reflections due to a strong dynamical diffraction effect.
Kikuchi lines appear sharply for a highly perfect and thick crystal.
5. Kikuchi patterns are effectively used for precise adjustment of a crystal orientation
by tilting the crystal for the Kikuchi lines to locate on the Bragg reflection spots.

16. (a)Kikuch lines: When the electrons inelastically scattered at a certain point O in a crystal cause Bragg reflections
from the front face (F) and the back face (B) of a crystal plane quite inclined against the direction of incident electrons I,
a pair of defect intensity and excess intensity lines which are called Kikuchi lines (KL) are produced at the positions
(directions) of the Bragg reflections 1 and 2. The intensity of Kikuchi line (1) near side of I is lower than that of the
surrounding area (directions). To the contrary, the intensity of Kikuchi line (2) far side of I is higher than that of the
surrounding area (directions).
The amplitude of the electrons inelastically scattered at the point O is large at low scattering angles
and becomes small as the scattering angle increases. The Bragg reflection (2) from the front face (F) of a crystal plane
due to the electrons inelastically scattered near the incident direction I forms strong excess and strong defect Kikuchi lines.
The Bragg reflection (1) from the back face (B) of the crystal plane due to the inelastically scattered electrons
far from the direction I compensates the contributions from the front face. However, since the compensation
by the latter is small, the low intensity (defect) KL (1) is formed near side of I, and the
high intensity (excess) KL (2) is formed far side of I.
(b) Transformation from Kikuch lines to Kikuchi band: When the inclined angle of the crystal plane becomes small
with respect to the direction of the incident electrons I, the difference of the amplitudes of inelastically
scattered electrons incident on the reflection planes F and B becomes small. As a result, the bell-shaped intensity
of Kikuchi lines becomes low, the symmetrical feature is lost, but an asymmetric (dispersion type) intensity starts to appear.
(c) Kikuchi band: When the crystal plane becomes symmetric with respect to the direction of the incident electrons (I),
the amplitudes of inelastically scattered electrons become equal for the Bragg reflections 1 and 2. As a result, the bell-shaped
intensity vanishes and then, the dispersion type intensity is formed due to a strong dynamical diffraction effect. In the angular
region between the positions (directions) 1 and 2, the intensity becomes higher than outside the region.
This high intensity band is called Kikuchi band (KB).

17. (d) Kikuchi pattern obtained from a Si single crystal: Many pairs
of Kikuchi lines due to high-order reflections are seen. In the
vicinity of a symmetric incidence, a Kikuchi band is seen
between “G = 220 reflection” and “G = -2-20 reflection”. The
low-intensity (defect (dark)) Kikuchi lines appear near side of
the incident beam direction, whereas the high-intensity (excess
(bright)) Kikuchi lines appear far side of the direction. (However
the Kikuchi pattern below is shown with reversal of bright and
dark.)