Robin N. Wilke

Hard X-ray imaging of bacterial cells: nano-diffraction and ptychographic reconstruction.

Ptychographic coherent X-ray diffractive imaging (PCDI) has been combined with nano-focus X-ray diffraction to study the structure and density distribution of unstained and unsliced bacterial cells, using a hard X-ray beam of 6.2keV photon energy, focused to about 90nm by a Fresnel zone plate lens. While PCDI provides images of the bacteria with quantitative contrast in real space with a resolution well below the beam size at the sample, spatially resolved small angle X-ray scattering using the same Fresnel zone plate (cellular nano-diffraction) provides structural information at highest resolution in reciprocal space up to 2nm(-1). We show how the real and reciprocal space approach can be used synergistically on the same sample and with the same setup. In addition, we present 3D hard X-ray imaging of unstained bacterial cells by a combination of ptychography and tomography.

Semi-transparent central stop in high-resolution X-ray ptychography using Kirkpatrick–Baez focusing

A semi-transparent central stop has been used for ptychographic coherent diffractive imaging to increase the effective dynamic range in the recording of the far-field diffraction patterns. In this way, the high flux density provided by nano-focusing Kirkpatrick–Baez mirrors can be fully exploited for high resolution and quantitative phase reconstructions.

Compound focusing mirror and X-ray waveguide optics for coherent imaging and nano-diffraction

A compound optical system for coherent focusing and imaging at the nanoscale is reported, realised by high-gain fixed-curvature elliptical mirrors in combination with X-ray waveguide optics or different cleaning apertures. The key optical concepts are illustrated, as implemented at the Göttingen Instrument for Nano-Imaging with X-rays (GINIX), installed at the P10 coherence beamline of the PETRA III storage ring at DESY, Hamburg, and examples for typical applications in biological imaging are given. Characteristic beam configurations with the recently achieved values are also described, meeting the different requirements of the applications, such as spot size, coherence or bandwidth. The emphasis of this work is on the different beam shaping, filtering and characterization methods.

Low-dose three-dimensional hard x-ray imaging of bacterial cells

We have imaged the three-dimensional density distribution of unstained and unsliced, freeze-dried cells of the gram-positive bacterium Deinococcus radiodurans by tomographic x-ray propagation microscopy, i.e. projection tomography with phase contrast formation by free space propagation. The work extends previous x-ray imaging of biological cells in the simple in-line holography geometry to full three-dimensional reconstruction, based on a fast iterative phase reconstruction algorithm which circumvents the usual twin-image problem. The sample is illuminated by the highly curved wave fronts emitted from a virtual quasi-point source with 10 nm cross section, realized by two crossed x-ray waveguides. The experimental scheme allows for a particularly dose efficient determination of the 3D density distribution in the cellular structure.

High-dynamic-range coherent diffractive imaging: ptychography using the mixed-mode pixel array detector

The advantages of a novel wide dynamic range hard X-ray detector are demonstrated for (ptychographic) coherent X-ray diffractive imaging.

High-flux ptychographic imaging using the new 55 µm-pixel detector `Lambda' based on the Medipix3 readout chip

The Large Area Medipix-Based Detector Array (Lambda) has been used in a ptychographic imaging experiment on solar-cell nanowires. By using a semi-transparent central stop, the high flux density provided by nano-focusing Kirkpatrick–Baez mirrors can be fully exploited for high-resolution phase reconstructions.

Quantitative X-ray phase contrast waveguide imaging of bacterial endospores

Quantitative X-ray phase contrast imaging uniquely offers quantitative imaging information in terms of electron density maps allowing for mass and mass density determinations of soft biological samples (‘weighing with light’). Here, it was carried out using coherent X-ray waveguide illumination, yielding values of the mass and mass density of freeze-dried bacterial endospores (Bacillus spp.).

Versatility of a hard X-ray Kirkpatrick-Baez focus characterized by ptychography.

In the past decade Kirkpatrick-Baez (KB) mirrors have been established as powerful focusing systems in hard X-ray microscopy applications. Here a ptychographic characterization of the KB focus in the dedicated nano-imaging setup GINIX (Göttingen Instrument for Nano-Imaging with X-rays) at the P10 coherence beamline of the PETRA III synchrotron at HASLYLAB/DESY, Germany, is reported. More specifically, it is shown how aberrations in the KB beam, caused by imperfections in the height profile of the focusing mirrors, can be eliminated using a pinhole as a spatial filter near the focal plane. A combination of different pinhole sizes and illumination conditions of the KB setup makes the prepared optical setup well suited not only for high-resolution ptychographic coherent X-ray diffractive imaging but also for moderate-resolution/large-field-of-view propagation imaging in the divergent KB beam.

Hard X‑ray Detection Using a Single 100 nm Diameter Nanowire

Submicron sized sensors could allow higher resolution in X-ray imaging and diffraction measurements, which are ubiquitous for materials science and medicine. We present electrical measurements of a single 100 nm diameter InP nanowire transistor exposed to hard X-rays. The X-ray induced conductance is over 5 orders of magnitude larger than expected from reported data for X-ray absorption and carrier lifetimes. Time-resolved measurements show very long characteristic lifetimes on the order of seconds, tentatively attributed to long-lived traps, which give a strong amplification effect. As a proof of concept, we use the nanowire to directly image an X-ray nanofocus with submicron resolution.

Towards multi-order hard X-ray imaging with multilayer zone plates

Multilayer zone plates can be used for holographic imaging without an order-sorting aperture.