E. Vlieg, A (2-TYPE SURFACE DIFFRACTOMETER - MERGENCE OF THE Z-AXIS AND (2+2)-TYPE GEOMETRIES(3)), Journal of applied crystallography, 31, 1998, pp. 198-203
It is shown that the addition of an azimuthal detector rotation to a (
2 + 2)-type diffractometer makes it fully equivalent to a z-axis type.
Using this equivalence, the geometric correction factors for this (2
+ 3)-type diffractometer, which are needed to obtain structure factors
from measured integrated intensities, are derived. The (2 + 3)-circle
diffractometer combines the ideal resolution behaviour of a z-axis di
ffractometer with the mechanical simplicity and range of a (2 + 2)-cir
cle diffractometer. For sample alignment, two additional degrees of fr
eedom are needed, leading to a total of seven circles.