From Wikipedia,
the free encyclopedia
RHEED stands for
Reflection High Energy
Electron diffraction. RHEED is
quite similar to
LEED.
RHEED uses an
electron gun and a
fluorescent screen for
creating pictures showing the
structure and/or
morphology of a
crystal surface. RHEED uses
much higher electron energy
(5-100keV) and lower impact angles
(<5°) than LEED. The higher energy
sharpens the picture, while the
lower angle makes the electrons
just pass a few atomic layers into
the crystal. This makes RHEED
pictures represent the structure
of the surface, not the whole
crystal.
In RHEED, the
reciprocal lattice is
2-dimensional if the crystal is
single crystalline and the
surface is flat in
nanometer scale. This
characteristic makes the
reciprocal lattice appear as lines
instead of dots in 3-dimensional
case. This way the reciprocal
lattice lines touch the Ewald-sphere
more often than normal and the
Laue diffraction condition is
fulfilled quite often in the
forward direction of the electron
beam, where the fluorescent screen
is mounted. The diffraction image
changes in other cases, depending
on the
crystallinity and the
morphology of the crystal.
Pros of RHEED: Real-Time
Analysis: RHEED is often used for
monitoring crystal growth, as it
doesn't block the direction
vertical to the surface of the
crystal, which is observed. It's
also very sensitive to surface
roughness.
Especially for the crystals
that can be easily damaged,
MCP-RHEED is used.
