1, University of Sao Paulo, Sao Paulo, , Brazil
3, Cornell University, Ithaca, New York, United States
Three dimensional X-ray diffraction microscopy (3DXRD) is a powerful technique that provides crystallographic and spatial information of a large number, on the order of thousands, of crystalline grains in a sample simultaneously. A key component of every 3DXRD microscopy experiment is the near field detector which provides high resolution spatial information of the grains. We present a novel design for a semi-transparent, 8 megapixel, near field detector which provides double the sample to detector distance then currently possible. This allows larger sample environments, such as high/low temperature chambers, anvils, and tensile strain setups. Previously unattainable in situ and in operando 3DXRD experiments can now be performed.
As opposed to a typical single scintillator phosphor detector, this design, we call the Quad Near Field Detector, uses four quadrants. This enables a total field of view is 5 mm x 5 mm with an effective pixel size of 1.3 µm x 1.3 µm. Each quadrant has a dedicated scintillator phosphor and optical microscope. A number of technical challenges need to be overcome to make a multi-detector solution practical and useful.
Complications arise when going from a single to multiple phosphor configurations, such as relative phosphor alignment and microscope focusing. In all, forty nine parameters need to be defined to obtain high quality reconstructions. Many parameters can be resolved by careful mechanical design. For this reason a novel translation stage for focusing the microscopes was developed, tested, and implemented. The remaining twenty five parameters were addressed by a refinement algorithm.
The near field detector was calibrated and characterized at the Cornell High Energy Synchrotron Source using 40 keV X-rays from the high energy wiggler source. Correction methods were developed for the Quad Near Field Detector to correct for variations in intensity response and spatial distortion. Diffraction data of all four quadrants reproduced crystal orientation of both a ruby and a multi-crystal gold calibration samples.