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Spectro-ptychography offers improved spatial resolution and additional phase spectral information relative to that provided by scanning transmission X-ray microscopes (STXM). However, carrying out ptychography at the lower range of soft X-ray energies (e.g., below 200 eV to 600 eV) on samples with weakly scattering signals can be challenging. We present soft X-ray ptychography results at energies as low as 180 eV and illustrate the capabilities with results from permalloy nanorods (Fe 2p), carbon nanotubes (C 1s), and boron nitride bamboo nanostructures (B 1s, N1s). We describe optimization of low energy X-ray spectro-ptychography and discuss important challenges associated with measurement approaches, reconstruction algorithms, and their effects on the reconstructed images. A method for evaluating the increase in radiation dose when using overlapping sampling is presented., Comment: 32 pages, 7 figures

Self-assembled colloidal crystals have attracted major attention because of their potential as low-cost three- dimensional (3D) photonic crystals. Although a high degree of perfection is crucial for the properties of these materials, little is known about their exact structure and internal defects. In this study, we use tomographic scanning transmission X-ray microscopy (STXM) to access the internal structure of self- assembled colloidal photonic crystals with high spatial resolution in three dimensions for the first time. The positions of individual particles of 236 nm in diameter are identified in three dimensions, and the local crystal structure is revealed. Through image analysis, structural defects, such as vacancies and stacking faults, are identified. Tomographic STXM is shown to be an attractive and complementary imaging tool for photonic materials and other strongly absorbing or scattering materials that cannot be characterized by either transmission or scanning electron microscopy or optical nanoscopy.

Scanning transmission x-ray microscopes (STXM) focus monochromatic x-rays into an intense sub-30 nm diameter spot. Samples are then positioned at the focal plane and raster scanned through the spot while the transmitted x-rays are acquired to build up images at x-ray photon energies. In addition, x-ray absorption spectroscopy (XAS) can be performed by recording image sequences over a photon energy range of interest. STXMs excel at characterizing thin sections of inhomogeneous soft matter with their combination of high spatial ( Doctor of Philosophy (PhD)

Detailed information about the energies of the electronically excited and ionized states of atoms and molecules is of central importance to the understanding of the interaction of energetic radiation with matter. Such data permits a more complete understanding of various processes taking place in physics, chemistry or biology, with important areas of application including electron and X-ray microscopy, space physics and chemistry or any other area where energetic radiation is used. This work documents the improvements and performance of a variable scattering angle energy loss spectrometer used to investigate inner-shell electronic spectroscopy of gases and to map generalized oscillator strengths. Wide ranges of impact energy and scattering angle are used to study both electric dipole and non-dipole transitions. New spectroscopic studies include: (i) the observation of the non-dipole "B-state" in SF6 S 2 p edge at very high scattering angle (62°) and at 1550 eV impact energy, where it dominates the spectrum; (ii) the first experimental observation of the C 1s [arrow right] σg * transition in CO2 . Generalized Oscillator Strength (GOS) profiles were mapped systematically for a collection of molecules: in SF6 , the GOS for S 2p and S 2s were extended up to very high momentum transfer, while the GOS for F 1s was mapped here for the first time. GOS curves were also obtained for all edges in CO 2 , COS and CS2 , some of them revealing their shapes for the first time. Where available, the results were compared to theoretical calculations. This work greatly extends previous reported studies of GOS for inner-shell excitation. Doctor of Philosophy (PhD)

In contrast to photoabsorption techniques, which are subject to electric dipole selection rules, electron energy loss spectroscopy (EELS) can provide a more complete investigation of atomic and molecular electronic structure. This is due to the added capability of accessing dipole and/or spin forbidden electronic transitions under conditions of significant momentum transfer. This work documents the design, construction and performance of a new, high resolution, variable scattering angle, variable impact energy electron spectrometer (McVAHRES) which has been used to investigate electronic transitions in gas phase atoms and molecules under both dipole and non-dipole conditions. The home-built instrument features a complex electron optics system and a sophisticated, computer-interfaced electronics system which allows a high degree of flexibility with regards to control and acquisition. This permits a wide range of experimental conditions. New spectroscopic studies include the observation of spin-forbidden, C is core excited triplet states in C₂H₄, C₂H₂, and C₆H₆. The momentum transfer dependence of the (C 1sˉ¹, π*) ³π state of CO was also investigated. These results are compared to the results of theoretical calculations. Generalised Oscillator Strengths (GOS) as a function of momentum transfer were derived for the S 2p edge of SF6. This work greatly expands previous results reported in the literature. Finally, an interesting feature was observed in the S 2p spectrum of SF₆, which displays quadrupolar momentum transfer behaviour. Doctor of Philosophy (PhD)

Inner-shell electron energy-loss spectroscopy (ISEELS) is an electron impact technique for the examination of inner-shell excitation of matter in the soft X-ray energy range between 20 and 1000 eV. It has long been utilized to study the core-excitation spectra of atoms and small organic or inorganic molecules. This thesis demonstrates the extension of such investigations to large organometallic complexes and organosilicon compounds in the gas phase. Measured under low momentum transfer conditions (>2.5 keV impact energy and small scattering angle, ≤2∙), where the spectra are dominated by electric-dipole-allowed transitions, ISEELS spectra have been recorded for transition metal carbonyls Fe(CO)₅, Fe₂(CO)₉ and CO₂(CO)x; metallocenes Fe(C₅H₅)₂, CH₂CH-C₅H₄FeC₅H₅, C₄H₉-C₅H₄FeC₅H₅ and Co(C₅H₅)₂; mixed-ligand complexes C₅H₅TiCl₃, C₆H₆Cr(CO)₃, organopolysilanes (CH₃)₃SiSi(CH₃)₃ and Si[Si(CH₃)₃]₄ as well as related compounds TiCl₄, C₅H₆ and (C₅H₆)₂. The spectral features have been assigned on the basis of comparison with the spectra of the free ligands and with a few previous studies of related organometallic/organosilicon species, along with extended Hückel molecular orbital calculations. The spectra provide novel insight into how inner-shell excitation spectroscopy reflects the metal-ligand bonding in these complexes and ligand-ligand interaction via the central metal atom. All the O 1s spectra are similar to each other, and the C 1s and metal 2p spectra of related compounds in a series (e.g., carbonyl complexes or metallocene derivatives) also have a similar shape, suggesting similar origins of the spectral features. Small variations through each series have been interpreted in terms of changes in the electronic structure associated with changing substituents. The metal 2p spectra are found to be surprisingly sensitive to the identity of the ligands present in the complexes and/or the character of the metal-ligand bonding. A resonance associated with the Si-Si σ* antibonding molecular orbital is identified at 102.5 eV in the Si 2p spectra of the two organosilicon compounds. Doctor of Philosophy (PhD)