We describe a hybrid pixel array detector (electron microscope pixel array detector, or EMPAD) adapted for use in electron microscope applications, especially as a universal detector for scanning transmission electron microscopy. The 128×128 pixel detector consists of a 500 µm thick silicon diode array bump-bonded pixel-by-pixel to an application-specific integrated circuit. The in-pixel circuitry provides a 1,000,000:1 dynamic range within a single frame, allowing the direct electron beam to be imaged while still maintaining single electron sensitivity. A 1.1 kHz framing rate enables rapid data collection and minimizes sample drift distortions while scanning. By capturing the entire unsaturated diffraction pattern in scanning mode, one can simultaneously capture bright field, dark field, and phase contrast information, as well as being able to analyze the full scattering distribution, allowing true center of mass imaging. The scattering is recorded on an absolute scale, so that information such as local sample thickness can be directly determined. This paper describes the detector architecture, data acquisition system, and preliminary results from experiments with 80–200 keV electron beams.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1431927615015664

High Dynamic Range Pixel Array Detector for Scanning Transmission Electron Microscopy

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 Gottingen 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.

/pdf/compound-focusing-mirror-and-x-ray-waveguide-optics-for-4ragtj4acg.pdf

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

https://journals.iucr.org/m/issues/2015/03/00/cw5005/cw5005.pdf

X-ray imaging detectors for synchrotron and XFEL sources.

The accuracy of X-ray diffraction data is directly related to how the X-ray detector records photons. Here we describe the application of a direct-detection charge-integrating pixel-array detector (JUNGFRAU) in macromolecular crystallography (MX). JUNGFRAU features a uniform response on the subpixel level, linear behavior toward high photon rates, and low-noise performance across the whole dynamic range. We demonstrate that these features allow accurate MX data to be recorded at unprecedented speed. We also demonstrate improvements over previous-generation detectors in terms of data quality, using native single-wavelength anomalous diffraction (SAD) phasing, for thaumatin, lysozyme, and aminopeptidase N. Our results suggest that the JUNGFRAU detector will substantially improve the performance of synchrotron MX beamlines and equip them for future synchrotron light sources.

/pdf/fast-and-accurate-data-collection-for-macromolecular-1rsw05mw5k.pdf

Fast and accurate data collection for macromolecular crystallography using the JUNGFRAU detector.

Finite element simulations are carried out to follow the evolution of residual stresses in Ti-7Al ( α -hcp) alloy, as developed under an applied stress gradient. A model built upon phenomenological mesoscopic field dislocation mechanics is employed to simulate the deformation behavior. Model predictions are validated with results generated from high energy X-ray diffraction experiments using synchrotron radiation. These experiments provide for important simulation input, viz. grain positions and orientations, and strain rate sensitivities of the prismatic and basal slip systems of Ti-7Al. X-ray diffraction data obtained from individual grains enabled calculation of strain rate sensitivities of the prismatic and basal slip systems and the values are estimated as  ∼ 0.04 and  ∼ 0.02 respectively. Residual stresses at the length scale of individual grains and subgrains are successfully predicted and validated against experimental data. A key achievement of the present work is the measurement and simulation of residual stress gradients within individual grains. Conclusions from this work are that grains deform mainly via prismatic slip, and accurate characterization of rate-sensitivity is needed to model the development of grain-level residual stresses.

Study of residual stresses in Ti-7Al using theory and experiments

An x-ray pixel array detector (PAD) capable of framing up to 1 kHz is described. This hybrid detector is constructed from a 3-side buttable, 128×128 pixel module based upon the mixed-mode pixel array detector (MMPAD) chip developed jointly by Cornell and Area Detector Systems Corporation (Poway, CA). The chip uses a charge integrating front end for a high instantaneous count rate yet with single photon sensitivity. In-pixel circuitry utilizing a digital overflow counter extends the per frame dynamic range to >4×107 x-rays/pixel. Results are shown from a base configuration of a 2×3 module array (256×384 pixels).

http://bigbro.biophys.cornell.edu/publications/289%20Tate.pdf

C Strohman

Papers

A Medium-Format, Mixed-Mode Pixel Array Detector for Kilohertz X-ray Imaging