Show Abstract ▼

Abstract: When an object is illuminated by a source, the resulting exit wave is a complex function intricately connected to the object's structure. Generally speaking, the wave's modulus corresponds to the object's transmittance, while its phase represents the cumulative phase shift relative to free space, caused by the object's refractive index as the wave traverses it. Therefore, to fully characterise the object, both the modulus and phase of the exit wave are required. However, detectors only measure the intensities (the modulus squared) of the waves striking the detector. The modulus can thus be easily obtained by taking the square root of the measured intensity. The phase, on the other hand, is much more challenging to determine. Any potential phase configuration could theoretically produce the same measured intensity, leading to what is known as the 'Phase Retrieval Problem', whereby the true phases that were lost during the experiment are not easily recovered. Ptychography offers a possible solution to the phase retrieval problem. Multiple diffraction intensity patterns are obtained by scanning a finite probe over an extended specimen with sufficient overlap between adjacent illumination positions. Combined with suitable iterative reconstruction algorithms, these measured diffraction patterns can be effectively utilised to accurately determine both the amplitude and phase of the object's exit wave, providing a robust approach that significantly enhances the ability to retrieve complete structural information about a specimen. Ptychography can be combined with X-ray absorption spectroscopy by using an X-ray beam of tuneable energies at each scan position. The diffraction patterns are now collected when the X-rays are scanned over absorption edges of specific elements, providing chemical information, in addition to high resolution reconstructions. This method has been dubbed 'Spectro-Ptychography'. Our work aims to push the limits of ptychography by employing it to analyse various butterfly scales. These scales are intricate self-assemblies of proteins that form complex structures. Beyond exhibiting pigment colour—where specific compounds absorb particular wavelengths of light—butterfly scales are also remarkable examples of structural colour, where their unique structures manipulate light in specific ways. We will showcase the application of spectro-ptychography on butterfly scales and demonstrate how we extracted detailed 3D spatial and chemical information from the dataset, aiding in our understanding of both 'pigment colour' and 'structural colour'. Preliminary results reveal distinct chemical variations in the carbon and oxygen signatures across different regions of a butterfly scale. By segmenting the scale into defined classes, we gain deeper insights into the chemical compositions of each specific segment, enhancing our understanding of its complex structure.

Open Access

Show Abstract ▼

Abstract: Imaging of nanoscale magnetic textures within extended material systems is of critical importance to both fundamental research and technological applications. While high-resolution magnetic imaging of thin nanoscale samples is well established with electron and soft x-ray microscopy, the extension to micrometer-thick systems currently requires hard x rays, which limits high-resolution imaging to rare-earth magnets. Here, we overcome this limitation by establishing soft x-ray magnetic imaging of micrometer-thick systems using the pre-edge phase x-ray magnetic circular dichroism signal, thus making possible the study of a wide range of magnetic materials. By performing dichroic spectroptychography, we demonstrate high spatial resolution imaging of magnetic samples up to 1.7  μ⁢m thick, an order of magnitude higher than conventionally possible with soft x-ray absorption-based techniques. We demonstrate the applicability of the technique by harnessing the pre-edge phase to image thick chiral helimagnets, and naturally occurring magnetite particles, gaining insight into their three-dimensional magnetic configuration. This new regime of magnetic imaging makes possible the study of extended non-rare-earth systems that have until now been inaccessible, including magnetic textures for future spintronic applications, non-rare-earth permanent magnets for energy harvesting, and the magnetic configuration of giant magnetofossils.

Open Access

Show Abstract ▼

Abstract: This study reports the characterisation of human dental enamel caries using synchrotron nanoscale correlative ptychography and spectroscopic mapping in combination with scanning electron microscopy. A lamella ̴2.4 µm thick was extracted from a carious enamel region of a tooth using focused ion beam-scanning electron microscopy and transferred to two synchrotron beamlines to perform hard X-ray nano-fluorescence spectroscopy simultaneously with differential phase contrast mapping at a beam size of 50 nm. Soft X-ray ptychography data was then reconstructed with a pixel size of 8 nm. The two dimensional variation in chemistry and structure of carious enamel was revealed at the nanoscale, namely, the organisation of hydroxyapatite nano-crystals within enamel rods was imaged together with the inter-rod region. Correlative use of electron and X-ray scanning microscopies for the same sample allowed visualisation of the connection between structure and composition as presented in a compound image where colour indicates the relative calcium concentration in the sample, as indicated by the calcium Kα fluorescence intensity and grey scale shows the nanostructure. This highlights the importance of advanced correlative imaging to investigate the complex structure-composition relationships in nanomaterials of natural or artificial origin.