MIT MRSEC - Materials Reseach Science and Engineering Center

X-ray Diffraction Shared Experimental Facility

Bruker Cobalt Source D8 with GADDS

Instrument Status

This instrument is fully functional. If you would like to be trained in its use, please contact facility staff.

Instrument Description

The General Area Detector Diffraction System (GADDS) posesses three unique capabilities that are not found in any of our other instruments:

  1. The source is Co instead of Cu, therefore, mitigating fluorescence from Fe and Co containing samples.
  2. A two-dimensional area detector, which captures more of the diffracted X-rays and facilitates study of materials that are textured, grainy, or under residual stress.
  3. Small beam spot size, used for micro-diffraction from very small samples, and capable of mapping across a sample.

The primary tradeoff is resolution, as diffraction peaks obtained from this instrument are very broad. This instrument is also capable of some basic transmission SAXS and GISAXS measurements.

This system uses a conventional 1.6kW sealed tube cobalt anode. Incident-side optics include a variety of double-pinhole collimators and monocapillary devices, which are used to adjust the beam size, intensity, and divergence. The beam diameter for this instrument can range from 0.05 to 0.8 mm depending on the choice of collimator.

The goniometer is a chi-cradle type, with full phi axis rotation and x-y-z translation. Including omega, this gives six positioning axes for the sample (not including the detector axis, 2Theta). With this in mind, the instrument can be used for some basic single crystal diffraction analysis. However, the ranges of the axes are somewhat limited, as care must be taken to avoid collisions.

The real power of this instrument is in its detector. We have a Vantec-2000, which has a very wide dynamic range and a maximum frame resolution of 2048x2048 pixels. Two-dimensional detectors facilitate the study of grainy, textured, and stressed materials, because the detector captures a slice of the Ewald diffraction sphere instead of a single point.

A low temperature Oxford Cryosystems Cryostream 700 is available for in-situ cooling from room temperature to 77º K. In addition, we have collimator-mounted beam stops and a detector-mounted beam stop with a helium tube to reduce air scatter. These devices enable us to use the GADDS system to collect some basic WAXS and SAXS data.

Bruker D8 GADDS

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GADDS