Tomographic X-ray phase reconstructions of an atomic force microscope tip with a spatial resolution of better than 900 nm are presented. The data was acquired using an X-ray energy of 1.83 keV using ...a zone plate based microscope at a third generation synchrotron, the Advanced Photon Source at the Argonne National Laboratory. The phase tomographic data is quantitatively accurate and we confirm that the deduced refractive index is in agreement with the known properties of the sample. Our results open the way for full 3D imaging of the complex refractive index with sub-micron spatial resolution.
Ultrahigh-Resolution X-ray Tomography Haddad, W. S.; McNulty, I.; Trebes, J. E. ...
Science (American Association for the Advancement of Science),
11/1994, Volume:
266, Issue:
5188
Journal Article
Peer reviewed
Ultrahigh-resolution three-dimensional images of a microscopic test object were made with soft x-rays collected with a scanning transmission x-ray microscope. The test object consisted of two ...different patterns of gold bars on silicon nitride windows that were separated by $\sim$5 micrometers. Depth resolution comparable to the transverse resolution was achieved by recording nine two-dimensional images of the object at angles between -50 and +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a three-dimensional image by means of an algorithm using an algebraic reconstruction technique. A transverse resolution of $\sim$1000 angstroms was observed. Artifacts in the reconstruction limited the overall depth resolution to $\sim$6000 angstroms; however, some features were clearly reconstructed with a depth resolution of $\sim$1000 angstroms.
Differential phase contrast can be realised in the scanning transmission x-ray microscope by use of a detector with an appropriate configuration of detector elements. Use of such a configured ...detector significantly improves the ability to image specimens with low absorption contrast. A natural application is found in scanning fluorescence x-ray microprobe studies of biological specimens. We discuss the technique and several applications.
We predict the presence of strong dichroic effects induced by x-ray beams carrying orbital angular momentum (OAM). Taking the difference between spectra obtained with positive and negative OAM states ...allows the separation of quadrupolar from dipolar transitions at, e.g., the transition-metal K edges, enabling the study of the unoccupied states in the absence of strong core-hole effects. We study the dependence of OAM-induced x-ray dichroism on different polarization vectors and derive sum rules relating the integrated intensity to ground-state hole densities. Calculations of spectral line shapes for cuprates, manganites, and ruthenates confirm the strong OAM-induced dichroism and indicate the potential of this new spectroscopy in the fields of orbital physics and magnetism.
Phosphorus K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy was performed on phosphate mineral specimens including (a) twelve specimens from the apatite group covering a range of ...compositional variation and crystallinity; (b) six non‐apatite calcium‐rich phosphate minerals; (c) 15 aluminium‐rich phosphate minerals; (d) ten phosphate minerals rich in either reduced iron or manganese; (e) four phosphate minerals rich in either oxidized iron or manganese; (f) eight phosphate minerals rich in either magnesium, copper, lead, zinc or rare‐earth elements; and (g) four uranium phosphate minerals. The identity of all minerals examined in this study was independently confirmed using X‐ray powder diffraction. Minerals were distinguished using XANES spectra with a combination of pre‐edge features, edge position, peak shapes and post‐edge features. Shared spectral features were observed in minerals with compositions dominated by the same specific cation. Analyses of apatite‐group minerals indicate that XANES spectral patterns are not strongly affected by variations in composition and crystallinity typical of natural mineral specimens.
We measured static x-ray speckle contrast variation with the incident photon energy across a sample-specific absorption edge. In this paper, we present a theoretical description of this energy ...dependency consistent with our data. We found that the contrast depends mainly on the imaginary part of the complex index of refraction in the sample, as well as on the instrumental resolution. The speckle contrast decreases as the absorption cross section in the sample increases at the absorption edge. This result is not predicted by commonly used theory.
The dealloying process is directly imaged, for the first time, by using transmission X-ray microscopy for the case of an Ag–30at.% Au wire dealloyed under free corrosion in nitric acid. The ...propagation of a sharp dealloying front separating the alloy from nanoporous Au was observed by two-dimensional real-time in situ imaging at 30nm resolution and measured in detail in three dimensions by an ex situ nanotomography technique at fixed time intervals. The rate of the dealloying front propagation is independent of the dealloying time up to a 3μm depth, indicating that the dealloying process to this depth is dominated by interfacial effects (i.e. gold surface diffusion and/or silver dissolution) rather than long-range transport effects (i.e. diffusion of acid and corrosion product in and out of the porous layer). The constant dealloying rate corresponds to a constant silver flux and a constant current density, even though the potential might be fluctuating under free corrosion conditions and the interfacial area is shrinking as a function of time. Free corrosion in this system generates a high current density, implying it is driven by a chemical potential difference that is much higher than the critical potential.
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