Microscopy of gold microcrystals by coherent X-ray diffractive imaging.

摘要

The small wavelength and penetrating nature of X-ray radiation has long been used to solve the structure of materials. Inherent in these measurements is the loss of phase information in the intensity measurement; the so-called "phase problem." Third generation synchrotrons provide X-ray beams with coherence volumes on the cubic micron size scale, allowing the coherent illumination of small crystals. By measuring the diffraction from such an experiment and iterative phasing the coherent X-ray diffraction (CXD) pattern, we can create a sort of lenless X-ray microscope, where the lens is replaced by a calculation. The iterative algorithms explored include Error Reduction and Fienup's Hybrid Input/Output and Elser's Difference Map. In this thesis, we present the result of iteratively phasing the diffraction from a single Gold crystal to yield its 3D density map. Further, simulations are performed to determine what effects noise may or may not be creating in the result. The simulations performed here indicate that those artifacts induced by reasonable levels of noise are not of a kind that might reasonably be confused with physical results.