GARRATT RESEARCH GROUP
GROWTH, MEASUREMENT, AND ANALYSIS TOOLS
Synthesizing Data from Nature
SCANNING X-RAY DIFFRACTION
Scanning a beam of x-rays enables us to measure location dependent transitions in diamond  structure creating a picture variation in macroscale structure over mm lengths. The s-XRD optics solution parallelizes, monochromates, and confines Cu Kα beams to a 300 µm spot size with 0.003° peak resolution (10.8 arcseconds). High resolution stage movement (±5 µm XY), and a CCD camera allows us to visually navigate the sample via 4:3 aspect ratio images up to 800x magnification. These features enable navigation to specific sites for point measurement, line scans, and small to large area mapping. An Eulerian cradle enables examination of nearly the entire diffraction space as need arises through out-of-plane χ and in-plane φ rotation axes. System capabilities include; scanning XRD, residual stress, pole figure, grazing incidence (out of plane), reflectivity, and phase identification measurements.
QUANTITATIVE BIREFRINGENCE
Quantitative birefringence (QB) is be used to assess the degree of intrinsic strain in single crystal samples. The QB system employs rotational stepper motor with 0.0001° precision and an in-house developed (by students) computer program in MatLab and Python to control, correlate, and compile transmission images of 633 nm laser light. Quantitation in birefringence images enables the amount of strain in the system to be assess relative to the value of sin δ, which is the change in polarization angle of birefringent light passing through the sample. Strain will be reflected as a proportional change in sin δ. This system was initially developed to analyze diamond samples, which is transparent to 633 nm light. Each image is the product of polarized light passed through two quarter-wave plates rotated at specific angles relative to each other and received by a CMOS CCD camera. The final image is a compiled image of polarized light. Structural defects such as stacking faults, twinning, dislocations, and growth sectors will rotate the polarized light as it passes through, producing an image of strain distributions. Analysis tools automatically identify and extract features associated with different types of defects based on the strain pattern produced.
DIAMOND REACTORS
Diamond crystals are synthesized in our group using microwave plasma assisted chemical vapor deposition. Diamond reactors like the one pictured here are designed to strike and maintain a hot plasma composed primarily of hydrogen and methane at ~2200 degrees Celsius. From this plasma crystals undergo a process of etching and growth to form polycrystalline or single crystal bulk samples. Our group explores diamond growth in constrained systems to understand the interplay between molecular growth species and electric fields from the plasma, temperature distributions on the substrate, and crystal morphologies. These dictate the ultimate structure and performance of diamond for electronics and quantum applications.
DATA ANALYSIS TOOLS
Analysis tools developed in our group allow us to process very large sets of data quickly and explore the data space created by scanning techniques more fully. This in turn allows us to understand the process structure relationships so we can engineer better growth systems and processes.
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Data acquired using x-ray diffraction, quantitative birefringence, or other techniques is multi-layered. These data sets contain peaks to be modeled from which additional features describing the physical arrangement of atoms, or effects of those arrangements, can be quantified. Scanning measurements add another layer to this picture by allowing us to interpolate effects of adjacent or distant structures, and determine how they affect each other or arise out of the conditions of crystal synthesis.
RADIATION-SOLID INTERACTION MODELING
Diamond makes for an excellent radiation sensor due to it's extreme resistance to radiation-induced damage. Our group models the effects of different radioactive particles on the structure of diamond using computer simulation software GEometry ANd Tracking 4 (GEANT4, or G4) for the nuclear physics community and Stopping Range of Ions in Matter (SRIM) for the materials science community. These tools allow us to predict and understand the effects of radiation on the formation of vacancy complexes in diamond, so-called vacancy centers like the NV center, and the performance of diamond in harsh radiation environments like those in the facility for Rare Isotope Beams (FRIB)
FTIR SPECTROSCOPY
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