Kuppili, Venkata Sree Charan; (2019) X-ray far-field ptychotomography at I13-1 diamond light source. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

X-ray far-field ptychography has emerged as an important imaging technique in order to obtain high resolution, complex transmission maps of nanostructures and nanomaterials. Ptychography achieves this by collecting X-ray far-field diffraction patterns at pre-defined scan positions which are later processed using iterative phase-retrieval algorithms. It has been demonstrated that features as small as 10 nm could be resolved using this technique. Ptychography can be combined with tomography in order to obtain the same in three dimensions. Known as ptychographic-nanoCT or ptychotomography, has proved to be an effective tool to image nanomaterials in three dimensions with resolutions as high as 16 nm. Ptychotomography played a crucial role in imaging nanostructured materials such as egg shells, solar cells and catalysts. This thesis will document various theoretical, experimental and algorithmic factors involved in carrying out ptychotomography. This work will demonstrate the feasibility of ptychography and its allied tomographic imaging technique at I13-1, Diamond Light Source UK. Along with this, this work will also demonstrate two novel 3D imaging modalities namely partially local ptychotomography and limited angle ptychotomography. The first two chapters will introduce theoretical concepts involving basic properties of X-rays with special emphasis on coherence. Synchrotron sources as an extended coherent source will be motivated. Ptychography will be explained next, ptychography will be motivated as a scanning variant of coherent diffraction imaging technique. This chapter will conclude with introduction to tomography along with the details of combining ptychography with tomography. The next chapter will document the methodology of conducting ptychotomography at a synchrotron source with special emphasis on I13-1 Diamond Light Source. Instrumentation available at I13-1 will be documented, with commentary on the influence of the available instrumentation on the quality of ptychographic and tomographic imaging. This chapter will conclude with listing author’s contributions to I13-1. The results chapter will encompass four separate sections, the first will discuss various practical aspects of ptychography with emphasis on obtaining optimum ptychographic reconstructions. The next section will talk about partially local ptychotomography along with motivating ptychography as a tool for beamline assessment and characterisation. The section on limited angle ptychotomography will introduce novel imaging modalities to image extended samples from limited angular views. This chapter will conclude with the section listing author‘s contributions to projects involving other beamlines. This work will conclude with a discussion on the necessary steps needed to optimise ptychography, tomography at I13-1 along with discussing the existing limitations of ptychotomography and possible avenues for extending and improving this technique. Appendix sections will provide supporting information pertaining to various sections discussed through out this work.

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