|
||
 | ||
| Contents -> FOUR-CIRCLE REFERENCE -> Four-Circle Modes | |
|
|
| spec Manual | |
4.4. - Four-Circle ModesAs noted above, because there are three Euler angles (  , , )
while the direction
of the scattering vector
Q is specified by only two angles,
there is a degeneracy associated with the transformation from
(H,K,L)
to
(2,,,).
The degeneracy is resolved in
fourc
by providing a constraint.
In
fourc,
the different constraints are
called
modes.
The value of the
g_mode geometry parameter
determines the
prevailing mode.
Fourc defines several angles in order to specify certain of the modes. The angle  is defined
as
= - (2)/2, and is referred to as
OMEGA. The angle  (referred to as
AZIMUTH) specifies a counter-clockwise
rotation about the diffraction vector.
The zero of is determined by a reference
vector, different from the diffraction vector.
The azimuthal angle is defined to be zero
when this vector is in the diffraction plane.
The angles  (ALPHA) and
 (BETA) are defined
such that the angles between
the azimuthal reference vector and the incident and scattered X-rays
are 90°- and 90°-, respectively.
One commonly used azimuthal reference
vector is the sample's surface normal, which
then makes and correspond
to the incident and exit angles of the X-rays on the surface.
g_mode = 0) |
Top
|
|
|
|
 Prev | Next 
|
|