WK.03 Modeling and Refinement of Nanoparticle Structures from Diffraction Data
Nanomaterials are becoming of increasing importance as complex, functional materials and without a doubt, this trend will continue. Whereas we have a well-developed set of tools to structurally characterize crystalline materials from single crystal and powder diffraction data, tools to extract the same amount of structural information from nanomaterials are just emerging. Along with new tools comes the challenge of making them available to the wider community and more importantly providing the training needed to enable young crystallographers to enter this field.
Filling this need is the aim of this workshop proposal centered around the modeling and refinement programs PDFgui and DISCUS. What is unique and new in this workshop is the focus on nanoparticles (particles with a diameter less than 100 nanometers) based on total scattering x-ray and/or neutron data. This is the first hands-on workshop that will cover approaches based on a bulk-like model (PDFgui) as well as the simulation of discreet particles (DISCUS). Past workshops at other venues co-organized by the PIs have covered individual parts separately and in discussions with colleagues and participants, the need for a focused workshop highlighting both modeling approaches became apparent.
This workshop is intended as a hands-on tutorial. Lectures by the organizers will give an outline of the scientific problems and challenges related to structural modeling of nanoparticles. The two modeling approaches and software packages will be briefly introduced. The main part of the day will be filled with hands-on tutorials using the two packages:
PDFgui (www.diffpy.org) is freely available and runs on Windows, MAC and Unix based platforms. The program enables refinement of a structural model to the experimental atomic pair distribution function (PDF). The program is usually used to model disordered bulk materials. However, the use of an envelope function for finite particles allows refining PDFs from spherical nanomaterials. A recent example of this technique applied to BaTiO3 nanoparticles can be found in "Probing Local Dipoles and Ligand Structure in BaTiO3 Nanoparticles" by Page et al., Chemistry of Materials 22, 4386 (2010) - DOI: 10.1021/cm100440p.
DISCUS (discus.sourceforge.net) employs an alternate strategy and allows one to create the actual finite particle and refine appropriate model parameters using an evolutionary algorithm. This is the approach of choice in cases where a bulk type model fails, e.g. interactions with organic capping molecules, core-shell architectures, or anisotropic shapes. Details were published recently in "Building and refining complete nanoparticle structures with total scattering data" by Page et al., J. Appl. Cryst., 44, 327 (2011) - DOI: 10.1107/S0021889811001968
We plan to use the same system for both hands-on modeling exercises and highlight the unique features and limitations of each approach. As mentioned earlier, this is the first workshop providing this type of comprehensive hands-on opportunity. Participants will be required to install both programs on their own laptops before coming to the workshop.
A related session on total scattering organized by the PI is part of the ACA 2012 program and is anticipated to showcase recent scientific results related to the workshop. To encourage early career participants in the workshop, we also plan to offer follow up 'office hours' during the conference to discuss the research projects of the participants. Details will be discussed with the conference organizers once this workshop proposal has been accepted.
08:00-09:00 - Welcome and introduction to nanoparticle analysis. T. Proffen
09:00-10:00 - Modeling of the spherical nanoparticle PDF and introduction to PDFgui and the hands-on example. K. Page
10:00-10:30 Coffee Break
10:30-12:00 - PDFgui hands-on example. T. Proffen / K. Page
12:00-13:00 Lunch (on your own)
13:00-14:00 - Creating /refinement of discreet nanoparticle models and introduction to DISCUS and the hands-on example. T. Proffen
14:00-15:00 - DISCUS hands-on (Part I). T. Proffen / K. Page
15:00-15:30 Coffee Break
15:30-17:00 - DISCUS hands-on (Part II). T. Proffen / K. Page
Oak Ridge National Laboratory
Neutron Scattering Science Division
Oak Ridge, TN 37831
Los Alamos National Laboratory
Lujan Neutron Scattering Center
Los Alamos, NM 87545
University of Erlangen
Department of Crystallography
$100 students and postdocs
$140 all others
This fee is separate from the registration fee but must be included with your registration. Fees increase after May 31, 2012.