WK.03 Reciprocal Space Visualization - MAX3D
When we use an area detector to collect diffraction data for single crystal structure analysis or polycrystalline solid or film texture analysis we rotate the sample around the φ or ω diffractometer axis and store the 3D pattern as distorted slices of reciprocal space. MAX3D is a visualization program which allows us to compile and view the data as a single object - a 3D plot of intensity vs. radial 2θ. Seeing the full diffraction pattern allows us to better determine crystal or film quality, identify weak super-lattice reflections or twinning, observe the details of diffuse or incommensurate scattering, monitor phase changes, enhance student understanding, etc.
The workshop will open with a discussion of reciprocal space and a description of how the all of the information on an area detector frame (not just Bragg spots) maps into RS. We will look at examples of "single crystal" diffraction showing crystal quality, protein diffraction, twinning, incommensurate scattering, diffuse scattering, quasicrystal diffraction. We will briefly discuss the origins of various scattering features. We will discuss how scanning strategies can be viewed and optimized to observe targeted diffraction features.
The participants will be given a brief introduction to texture analyses - the analyses of polycrystalline grain orientation distribution in solid materials. Mapping of 3D 'powder' diffraction will be demonstrated with examples from studies of metals, thin films, polymers and nano-materials.
The obvious teaching applications of the visualization of 3D diffraction patterns for the various types of materials studied will be emphasized. MAX3D can be used live to carefully examine student data, or can output videos of reciprocal space for later use.
The second part of the workshop will allow the participants to follow along with the instructor in a step by step rendering of a series of supplied data sets. The attendees will have installed the MAX3D software and tutorial data on their laptops in advance of the workshop. We will practice loading scans, paying attention to the voxel resolution limits of the laptops. We will load a known orientation matrix for the single crystal examples so that we can identify what we are looking at in terms of (fractional) HKL indices. We will look at tools for adjusting the transparency of the diffraction pattern to highlight its interesting features. We will use a 3D clipping volume to zoom in on an interesting region of reciprocal space and reload it at higher resolution. Tools for looking at 2D slices through the diffraction pattern will be demonstrated. For texture examples we will look at the overall pattern as well as isolated 2θ shells (pole figures). Options for saving images, 3D data volumes, and generating 1D average or sum plots will be covered.
In the final part of the workshop we will look at scans supplied by the participants. We will try to explain why certain data sets prove to be difficult to handle, or show evidence of short range ordering. Attendees can work alone, in small groups or use the projector to work in a larger group.
The software license, which normally carries an $800 fee charged by the developer (McMaster University), will be supplied to academic users for the workshop at no charge. It will give them continuing access to all features of MAX3D, as well as any future upgrades or new version releases.
MAX3D is no longer a unique software package, but it is still one of the better reciprocal space viewers, able to load large volumes of data and render beautiful, informative images. No matter which software a crystallographer uses, the routine, quick examination of 3D diffraction patterns is a habit every crystallographer should adopt. This workshop will give the participants a feel for how much untapped information is available in a diffraction pattern. Samples which are often considered bad may prove to be a lot more interesting than originally thought. Recognizing non-Bragg scattering features and knowing what may give rise to them can explain physical features of a material. At the very least, it can help one argue for publication of what characterization can be performed on a sample. On the other hand, one can also declare a difficult sample as 'bad' with much more confidence. Plotting 3D diffraction patterns is also an excellent teaching tool when introducing chemists, biochemists, physicists, materials engineers, and industrial clients to the power of crystallography.
1:00 - 2:00 Overview of MAX3D applications and features
2:00 - 3:00 Step by step analyses of tutorial data. Participants should follow along on their own computers
3:00 - 3:30 Break / Discussion
3:30 - 4:30 Visualization optimization and analyses of data provided by participants
Jim Britten, McMaster Analytical X-ray Diffraction Facility, McMaster University