224 research outputs found
Ordered mesoporous silica nanoparticles with and without embedded iron oxide nanoparticles: Structure evolution during synthesis
No full textThis work reports on the structural evolution during room temperature synthesis of hexagonally ordered mesoporous silica nanoparticles with and without embedded iron oxide particles. Oleic acid-capped iron oxide nanoparticles are synthesized and transferred to an aqueous phase using the cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). MCM-41 type silica and composite nanoparticles are fabricated via sol-gel synthesis. Aliquots are taken from the solution during synthesis to capture the particle formation process. Transmission Electron Microscopy (TEM) and Small Angle X-ray Scattering (SAXS) reveal a transition from a disordered to an ordered structure in both synthesis systems. Along with the evolution of structure, iron oxide nanoparticles acting as seeds at the early stages are relocated from the particle centers to the edges. Nitrogen sorption measurements for iron oxide-embedded mesoporous nanoparticles indicate surface areas as high as for the mesoporous silica nanoparticles without iron oxide.N
Reconstructing three-dimensional protein crystal intensities from sparse unoriented two-axis X-ray diffraction patterns. Corrigendum
No full textA figure in the article by Lan, Wierman, Tate, Philipp, Elser & Gruner [J. Appl. Cryst. (2017), 50, 985–993] is corrected.</jats:p
High-dynamic-range coherent diffractive imaging: ptychography using the mixed-mode pixel array detector
No full textCoherent (X-ray) diffractive imaging (CDI) is an increasingly popular form of X-ray microscopy, mainly due to its potential to produce high-resolution images and the lack of an objective lens between the sample and its corresponding imaging detector. One challenge, however, is that very high dynamic range diffraction data must be collected to produce both quantitative and high-resolution images. In this work, hard X-ray ptychographic coherent diffractive imaging has been performed at the P10 beamline of the PETRA III synchrotron to demonstrate the potential of a very wide dynamic range imaging X-ray detector (the Mixed-Mode Pixel Array Detector, or MM-PAD). The detector is capable of single photon detection, detecting fluxes exceeding 1 × 8-keV photons , and framing at 1 kHz. A ptychographic reconstruction was performed using a peak focal intensity on the order of 1 × photons within an area of approximately 325 nm × 603 nm. This was done without need of a beam stop and with a very modest attenuation, while `still' images of the empty beam far-field intensity were recorded without any attenuation. The treatment of the detector frames and CDI methodology for reconstruction of non-sensitive detector regions, partially also extending the active detector area, are described
Development Of Low-Noise Direct-Conversion X-Ray Area Detectors For Protein Microcrystallography
No full textProtein microcrystallography is an active field of study in the synchrotron community, due to the fact that many proteins of scientific interest produce only small, weakly-diffracting crystals. New detectors must be developed to improve data quality and facilitate new experimental protocols, such as low-flux single-shot diffraction from microcrystals. The pioneering work in microcrystallography has been done primarily with phosphor-coupled CCDs and, more recently, with photon-counting pixel array detectors. However, both technologies have drawbacks that inhibit further development of the field. Phosphorcoupled CCDs have a large point spread function and relatively low signal-tonoise ratio (on the order of 0.5-1) for single x-ray photons. Photon-counting pixel array detectors have superior noise performance, but suffer from large pixel size and detector systematics which deserve consideration. To fill the need for a detector with small pixels and low x-ray equivalent noise, a deep-depletion CCD has been developed with 24 [MICRO SIGN]m x 24 [MICRO SIGN]m pixels and a point spread < 50 [MICRO SIGN]m FWHM. This device is based on the direct detection of xrays in silicon, which yields a large number of charge carriers per stopped x-ray, such that the signal from a single x-ray photon far outweighs the detector read noise. The design of this device will be described, along with characterization and initial protein crystallographic measurements
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