The Reflectometry group at the University of Maryland is part of the DANSE project, a NSF-funded 12 million dollar project to develop software to enable new science to be performed with neutron scattering experiments. Our mission is to provide an extensible software platform for analyzing reflectometry data which individual researchers can adjust to suit their own needs.

The DANSE/Reflectometry group will provide analysis functionality through a set of libraries for reflectometry calculations, a fitting service for simultaneously refining multiple measurements to a common underlying model, and an extensible user interface for simplifying control. These components will be incrementally developed throughout the life of the project.

Offspecular example

DANSE supports direct manipulation of 1-D magnetic reflectometry profiles.

1-D Modeling

The 1-D models give the depth profile for material scattering density composed of a mixture of flat and continuously varying freeform layers. With polarized neutron measurements, scientists can study the sub-surface structure of magnetic samples. The architecture supports the addition of specialized layer types such as models for the density distribution of polymer brushes, and volume space modeling for proteins in bio-membranes. We will provide a number of these models as well as supporting user defined layer types for both structural and magnetic scattering densities.

Status: 1-D modeling is available in our current release, with a full graphical interface for simultaneous fitting with flat and free-form models. We are adding support for specialized model types.

3-D Modeling

Using measurements of the reflection away from the specular condition, information about in-place near-surface structures is available. We are developing software based on grazing incidence small angle scattering theory which can measure in-plane structural and magnetic scattering densities such as those appearing in nanoscale electronic devices. We plan to support a number of standard structures and arrangements in the plane, as well as providing support for freely varying models.

Offspecular example

Scattering from diblock-copolymer structures deposited on silicon grating. Preliminary data taken on NCNR-AND/R).

Status:Prototype 3-D modeling is completed, and we are expecting our first applications by spring of 2010.

Global Optimization

The key to analyzing reflectivity data is to use all of the information available. This means simultaneously refining multiple measurements of related systems with constraints between the models, and limiting the parameter search space to reasonable values based on independent measurements of the system and knowledge of what it contains. Our layered architecture can be accessed at different levels, from the scientist user who can define a specialized model for a single system and automatically have a graphical user interface to interact with the parameters and the data, to the application developer who can use the fitting service backend for distributed computing support while providing their own user interface.

Status: Simple global optimization software is available. This will evolve as the project progresses.

Data Reduction

While the primary responsible for data reduction lies with the instrument scientists and the institutes to which they belong, the DANSE reflectometry team is working closely with the NIST Center for Neutron Research and the Spallation Neutron Source to provide support for handling raw data for existing and forthcoming instruments.

Status: Early data reduction routines are available and in use at the NCNR.

Direct Inversion

Researchers at the NIST Center for Neutron Research are developing a technique for phase reconstruction and direct inversion based on measurements of the film of interest on constrasting substrates. Support for this technique will be made available first as libraries and later as part of the reduction and analysis user interfaces.

Status: Initial support for direct inversion is expected in spring of 2010.

Molecular Dynamics

As the DANSE project provides support for various molecular dynamics packages we will include routines for estimating the density profiles from the resulting simulations. This will allow users to compare simulations directly to data from the instruments, and computing resources permitting, adjust simulation parameters until a closer match can be found.

Status: Support for molecular dynamics is not expected until the final stages of the project.

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