Modelling 3-D Structures

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Offspecular geometry

Grazing incidence small angle scattering (GISAS) is a technique for examining surface features in the plane of the surface. Unlike specular reflectivity which only measures structure as a function of depth, and unlike SAS, which measures properties of the bulk, GISAS responds to changes in both depth and to the pattern of structures near the surface.

Offspecular data

Work is currently being done to expand further neutron reflectometry to the off-specular regime for the characterization of thin films with two-dimensional, ordered in-plane structures. The combination of this two-dimensional, in-plane information with the depth-profile that is routinely obtained from reflectivity data can produce a complete, 3-D description of both the structure and magnetic characteristics of these films. Work is also being done on Grazing Incidence Small Angle Scattering (GISAS) which can also give information about very complex 3-D structures.

The University of Maryland along with the NIST Center for Neutron Research (NCNR) are developing software which can easily be integrated into existing neutron modeling packages and will expand the accessibility of off-specular neutron reflectometry to the general scientific community. The basic geometry of the experimental procedure is shown in Figure 1. Figure 2 shows the process by which data is processed. The software will be able to easily integrate GISAS and off- specular reflectometry to provide a very rich description of samples and will allow models to be calculated in the Born Approximation (BA) and the Distorted Wave Born Approximation (DWBA).