MAGIK
Multiple Angle Grazing Incidence K (vector)
a reflectometer/diffractometer for measuring subsurface structures
The problem: measuring specular reflectivity, neutron
reflectometry provides structural information along a direction
perpendicular to the plane of a thin film or a multilayer sample:
typically interlayer spacing and/or roughness. Increasingly the
structure of objects within the planes is also of interest, and
this requires measurements at angles off the specular direction, i.e.,
for scattered neutrons having momentum transfer vector components parallel
to the film planes, where signals may be smaller. To address this
issue, it is important to find ways to accomplish two
tasks: increase the signal size while maintaining angular
resolution for these parallel components, and reduce data
acquisition time.
A MAGIK solution: Beyond simply
increasing incident neutron flux, putting more neutrons on the sample
can be accomplished by illuminating it with a beam that is relaxed in angular spread
in a direction parallel to the film plane compared to the tightly
collimated beam usually associated with high resolution in the parallel
direction. But how can this be done while maintaining the desired
parallel component resolution? The answer lies in tagging the
angular components of the incident beam and extracting the
corresponding reflectivities at each detector pixel. Data acquisition
time can be further reduced by use of a position sensitive detector
so that parallel processing of the signals arriving at detector pixels
located at off-specular angles may be achieved. An instrument called MAGIK
(Multiple Angle Grazing Incidence K) reflectometer that incorporates
both of these features is being designed for use in the NCNR expansion
guide hall.
