X-ray scattering studies of nanostructured patterned arrays - PhDData

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X-ray scattering studies of nanostructured patterned arrays

The thesis was published by Greving, David Stefan, in September 2020, University of Warwick.


X-ray resonant magnetic scattering (XRMS) has been used to investigate patterned arrays created using electron beam lithography. Diffraction from the repeating pattern has been measured close to the origin of reciprocal space. The impact of the spatial coherence of x-ray radiation is discussed in the context of reproducing rocking curves at various azimuthal rotation angles from patterned arrays of multilayered circular and elliptical islands. We show how traditional diffraction theory implicitly assumes a high coherence which has to be adapted to account for both the finite number of elements coherently illuminated by the beam and the specific experimental configurations used. This allowed a generic theoretic framework to be developed to describe the scattering from patterned arrays. The derived computational foundation is formulated in a specifically developed simulation framework, of modular code design allowing for efficient data processing, simulation, and fitting.

Utilising XRMS, and fitting the charge and magnetic scattering signals simultaneously, allowed quantitative fits to the in-plane diffraction data contained in rocking curves and the specular reflectivity from a patterned array of disk-like circular islands. The islands were spatially resolved into a three-dimensional chemical and magnetic profile revealing a core-shell structure. This structure is likely to be as a result from oxidation, affecting the surface of the islands. Simple models assuming at disks could not reproduce the data and failed to account for the modulations in the intensity of the Bragg peaks, often by several orders of magnitude. A spatial model in which the islands were domed was developed in order to accurately reproduce the scattering data. The doming is likely to occur as a result of the prepatterning process used in sample production. The limited number of diffraction orders limits the precision of the modelling and we show how a grazing incidence small angle scattering (GISAXS) geometry can be exploited to easily and quickly obtain diffraction data over many orders, allowing a straightforward characterisation of the sample. The alternative experimental geometry is tested under laboratory conditions in which the coherence could be varied. Finally, XRMS measurements were also used in order to investigate the intra-island magnetic structure. Due to the shape anisotropy, magnetic vortex states form in the disk-like patterns. Fits of the magnetic hysteresis derived from the magnetic signal allow the structure of a magnetic vortex to be determined directly and indicate elliptical deformation of an magnetic vortex as it approaches the edge of the cylindrical host element.

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