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Abstract: A newly supplied 80 × 80 chromium compensated GaAs sensor with a matrix of 80 × 80 pixels on a 250 m pixel pitch has been characterised utilising microbeam mapping techniques at the Diamond Light Source. The GaAs:Cr sensor was mounted to a HEXITEC DAQ system before raster scanning an x-ray beam with area 25 × 25 m in steps of 25 m, providing sub-pixel resolution spectroscopic imaging. Scans were performed with incident x-ray energies ranging from 12 to 45 keV. Following processing of the data in MatLab 2019b an analysis of defects previously observed in etched GaAs wafers occured. Findings indicate the presence of regions with reduced charge collection efficiency where up to 88 % of incident events show significant charge loss, and changing charge carrier lifetimes across the sensor.

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Abstract: Thanks to the development of high-quality X-ray focusing optics during the past decades, synchrotron-based X-ray transmission microscopy techniques enable to study specimens with extremely high spatial resolution. However, on one hand at the expense of the field of view (100 μm x 100 μm) and on the other hand to the detriment of the photon energies range (below 20 keV), which significantly limits the specimens' scope to be investigated, particular- ly in material science. In this work, the so-called pixel super-resolution scanning transmission hard X-ray microscopy technique was developed, allowing to enlarge the field of view and drastically reduce the scanning time thanks to sub-pixel specimen scanning through a large number of X-ray probes created by biconcave para- bolic shaped refractive multi-lenses. High-resolution images with a spatial resolution corresponding to the X-ray (micro-) nanoprobe size are achieved, even if the pixel size of an imaging detector employed for data acquisition is much larger than that. Since the technique's key element is X-ray optics, the development and fabri- cation of one (two)-dimensional X-ray refractive multi-lenses (RMLs) for focusing high energy X-rays (17-35 keV) fabricated by deep X-ray lithogra- phy and electroplating technique are presented. The X-ray characterization of these optics and microscopy experiments performed at KARA (Germany), Diamond Light Source (England), and SPring-8 (Japan) synchrotron facilities are provided. Since the height of existing refractive multi-lenses still restricts the field of view (maximum in the mm range), the staircase array of RMLs inclined to the substrate was developed, allowing pixel super-resolution scanning transmission hard X-ray microscopy with a 1.64 cm × 1.64 cm field of view while keeping a 780 ± 40 nm resolution using 35 keV X-rays. The scanning time was only about four minutes. The unique capability of the pixel super-resolution scanning transmission hard X-ray microscopy has been demonstrated by imaging biomedical implant abutments fabricated via selective laser melting using Ti-6Al-4V. Accordingly, the investigation of extend- ed and thick specimens for material science has been demonstrated.

Open Access

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Abstract: Ever since the discovery of X-rays, tremendous efforts have been made to develop new imaging techniques for unlocking the hidden secrets of our world and enriching our understanding of it. X-ray differential phase contrast imaging, which measures the gradient of a sample’s phase shift, can reveal more detail in a weakly absorbing sample than conventional absorption contrast. However, normally only the gradient’s component in two mutually orthogonal directions is measurable. In this article, omnidirectional differential phase images, which record the gradient of phase shifts in all directions of the imaging plane, are efficiently generated by scanning an easily obtainable, randomly structured modulator along a spiral path. The retrieved amplitude and main orientation images for differential phase yield more information than the existing imaging methods. Importantly, the omnidirectional dark-field images can be simultaneously extracted to study strongly ordered scattering structures. The proposed method can open up new possibilities for studying a wide range of complicated samples composed of both heavy, strongly scattering atoms and light, weakly scattering atoms.

Open Access

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Abstract: The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX—a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

Open Access

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Abstract: This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron X-radiation. Characterized by X-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈ 4 nm thickness were studied in situ in an electrochemical cell under potential control (-0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by X-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at ≈ +0.8 V Cr-oxide was removed from the film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by X-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft X-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.