Chemistry Reference
In-Depth Information
w
-axis
Diffractometer
plane
y
-axis
f
-axis
w
-rotation
S
3
y
-rotation
FIGURE 9.7 The c-tilt is achieved by either iso-inclination (v-rotation) or side-inclination
(c-rotation).
9.2.5
-Tilt and Goniometer
Measurement of a stress value with the sin
2
c method requires at least the c-tilt, while
measurement of a stress tensor requires at least two rotation axes to achieve the c-tilt
and f-rotation. The c-tilt is defined as the angle between the sample normal and the
diffraction vector. Eulerian geometry has three sample rotation angles (v, c, f).
Hence, the c-tilt can be achieved by one of the two methods as shown in Figure 9.7.
One is the iso-inclination mode (also called the v-method or v-diffractometer) in
which both the sample normal (S
3
) and the diffraction vector are within the
diffractometer plane. The rotation axis is perpendicular to the diffractometer plane
containing the incident and diffracted beams. The other method is the side-inclination
mode (also called the c-method or c-diffractometer) in which the sample normal (S
3
)
is out of the diffractometer plane for all nonzero c-tilt angles. Both the sample normal
(S
3
) and the diffraction vector are within a plane perpendicular to the diffractometer
plane.
Since the c-tilt in the iso-inclination mode is achieved by a rotation axis parallel to
the main axes of a goniometer, the iso-inclination mode can be achieved with most
diffractometers. In a diffractometer with a u-2u configuration, the c-tilt is achieved
by v-rotation of the sample. The c-tilt is given by
c
59Þ
When v ¼ u, the diffraction vector and sample normal are in the same direction
(c ¼ 0). In a diffractometer with a u - u configuration, the c-tilt is achieved by the
difference between the incident angle (u
1
) and the detector angle (u
2
). The c-tilt is
given by
c ¼ vu
ð9
:
u
1
u
2
2
c ¼
ð9
:
60Þ
