A new fullerene network phase obtained from C70 at high‐pressure and high‐temperature

Fullerene networks are an exciting class of materials that may display exceptional physical properties. A new C₇₀‐fullerene network phase, synthesized at high‐pressure, 7 GPa, and high‐temperature, 600 °C, is presented. Its structure, determined by Rietveld analysis of the X‐ray diffraction data combined with density functional theory modeling, consists of puckered polymerized layers where each molecule is bonded to three neighbors through 2 + 2 cycloaddition bonds, a new polymeric configuration unseen in other fullerene networks. This new C₇₀‐fullerene network structure adds to the previous zigzag structures, demonstrating the potential of C₇₀ molecules as building blocks to synthesize new carbon phases. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

A curved image‐plate detector system for high‐resolution synchrotron X‐ray diffraction

The developed curved image plate (CIP) is a one‐dimensional detector which simultaneously records high‐resolution X‐ray diffraction (XRD) patterns over a 38.7° 2θ range. In addition, an on‐site reader enables rapid extraction, transfer and storage of X‐ray intensity information in ≤30 s, and further qualifies this detector to study kinetic processes in materials science. The CIP detector can detect and store X‐ray intensity information linearly proportional to the incident photon flux over a dynamical range of about five orders of magnitude. The linearity and uniformity of the CIP detector response is not compromised in the unsaturated regions of the image plate, regardless of saturation in another region. The speed of XRD data acquisition together with excellent resolution afforded by the CIP detector is unique and opens up wide possibilities in materials research accessible through X‐ray diffraction. This article presents details of the basic features, operation and performance of the CIP detector along with some examples of applications, including high‐temperature XRD.     

A high‐pressure and controlled‐flow gas system for catalysis research

A high‐pressure gas rig for in situ catalytic reactions at X‐ray absorption spectroscopy beamline (BM26A) has been developed. The rig enables catalysts to be studied in a variety of cells under well controlled and industrially relevant operation conditions. A large variety of gas mixtures can be generated and pressures of up to 50 bar with dry gas and 20 bar with wet gas (steam) can be obtained. Analyses of reaction products can be performed using an on‐line mass spectrometer.     

A large‐volume gas cell for high‐energy X‐ray reflectivity investigations of interfaces under pressure

A cell for the investigation of interfaces under pressure is presented. Given the pressure and temperature specifications of the cell, P≤ 100 bar and 253 K ≤T≤ 323 K, respectively, high‐energy X‐rays are required to penetrate the thick Al₂O₃ windows. The CH₄(gas)/H₂O(liquid) interface has been chosen to test the performance of the new device. The measured dynamic range of the high‐energy X‐ray reflectivity data exceeds 10^?8, thereby demonstrating the validity of the entire experimental set‐up.     

Achievements in high‐pressure science at the high‐brilliance energy‐dispersive X‐ray absorption spectrometer of ESRF,ID24

Although the idea of an X‐ray absorption spectrometer in dispersive geometry was initially conceived for the study of transient phenomena, the instrument at the European Synchrotron Radiation facility has been increasingly exploited for studies at extreme conditions of pressure using diamond anvil cells. The main results of investigations at high pressure obtained at beamline ID24 are reviewed. These concern not only fundamental topics, such as the local and the electronic structure as well as the magnetic properties of matter, but also geological relevant questions such as the behaviour of Fe in the main components of the Earth's interior.     

An asynchronous high‐speed synchrotron shutter

A high‐repetition‐rate mechanical shutter with asynchronous control and sub‐millisecond operation has been developed and tested for specialist X‐ray systems in the field of medical diagnostics and radiation therapy. Capacitor‐coupled linear voice coil actuators are utilized to achieve opening and closing speeds as fast as 700 µs for an aperture height of 4 mm. The design allows for asynchronous control, permitting slave operation of the shutter, a feature that is distinctly suitable for a number of applications including particle image velocimetry, where high‐frame‐rate operation must be accurately synchronized and triggered by the image acquisition sequence of the detector or timing device. The design and construction of the shutter also makes it ideal, with simple and limited modifications, for applications requiring larger apertures, in particular wide beams as found in many synchrotron beamlines.     

Resonant two‐magnon Raman scattering in high‐Tc cuprates

Resonance enhancement of one‐phonon, two‐phonon, and two‐magnon Raman scattering in a general, exactly solvable, multiband model is explained in a way that is in accordance with the general analytical properties of the total optical conductivity tensor. Using this approach, the charge‐transfer limit of the Emery three‐band model is examined to explain resonance enhancement of the two‐magnon Raman spectra of high‐T_c cuprates, which is found in experiments to be of 3 orders of magnitude. While previous Raman and optical conductivity analyzes of the cuprates, based on the single‐band Hubbard model, are found to be consistent with the picture where one hole per one CuO₂ unit is localized on the Cu ion, the present three‐band approach allows the study of the opposite, strong copper‐oxygen hybridization limit, which is found to be in agreement with the results of nuclear magnetic resonance (NMR) and one‐phonon Raman scattering experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

A robust method for high‐precision quantification of the complex three‐dimensional vasculatures acquired by X‐ray microtomography

The quantification of micro‐vasculatures is important for the analysis of angiogenesis on which the detection of tumor growth or hepatic fibrosis depends. Synchrotron‐based X‐ray computed micro‐tomography (SR‐µCT) allows rapid acquisition of micro‐vasculature images at micrometer‐scale spatial resolution. Through skeletonization, the statistical features of the micro‐vasculature can be extracted from the skeleton of the micro‐vasculatures. Thinning is a widely used algorithm to produce the vascular skeleton in medical research. Existing three‐dimensional thinning methods normally emphasize the preservation of topological structure rather than geometrical features in generating the skeleton of a volumetric object. This results in three problems and limits the accuracy of the quantitative results related to the geometrical structure of the vasculature. The problems include the excessively shortened length of elongated objects, eliminated branches of blood vessel tree structure, and numerous noisy spurious branches. The inaccuracy of the skeleton directly introduces errors in the quantitative analysis, especially on the parameters concerning the vascular length and the counts of vessel segments and branching points. In this paper, a robust method using a consolidated end‐point constraint for thinning, which generates geometry‐preserving skeletons in addition to maintaining the topology of the vasculature, is presented. The improved skeleton can be used to produce more accurate quantitative results. Experimental results from high‐resolution SR‐µCT images show that the end‐point constraint produced by the proposed method can significantly improve the accuracy of the skeleton obtained using the existing ITK three‐dimensional thinning filter. The produced skeleton has laid the groundwork for accurate quantification of the angiogenesis. This is critical for the early detection of tumors and assessing anti‐angiogenesis treatments.     

Design and performance of an ultra‐high‐vacuum‐compatible artificial channel‐cut monochromator

The design and performance of a novel ultra‐high‐vacuum‐compatible artificial channel‐cut monochromator that has been commissioned at undulator beamline 8‐ID‐I at the Advanced Photon Source are presented. Details of the mechanical and optical design, control system implementation and performance of the new device are given. The monochromator was designed to meet the challenging stability and optical requirements of the X‐ray photon correlation spectroscopy program hosted at this beamline. In particular, the device incorporates a novel in‐vacuum sine‐bar drive mechanism for the combined pitch motion of the two crystals and a flexure‐based high‐stiffness weak‐link mechanism for fine‐tuning the pitch and roll of the second crystal relative to the first crystal. The monochromator delivers an exceptionally uniform and stable beam and thereby improved brilliance preservation.     

A miniature X‐ray emission spectrometer (miniXES) for high‐pressure studies in a diamond anvil cell

Core–shell X‐ray emission spectroscopy (XES) is a valuable complement to X‐ray absorption spectroscopy (XAS) techniques. However, XES in the hard X‐ray regime is much less frequently employed than XAS, often as a consequence of the relative scarcity of XES instrumentation having energy resolutions comparable with the relevant core‐hole lifetimes. To address this, a family of inexpensive and easily operated short‐working‐distance X‐ray emission spectrometers has been developed. The use of computer‐aided design and rapid prototype machining of plastics allows customization for various emission lines having energies from ～3 keV to ～10 keV. The specific instrument described here, based on a coarsely diced approximant of the Johansson optic, is intended to study volume collapse in Pr metal and compounds by observing the pressure dependence of the Pr Lα emission spectrum. The collection solid angle is ～50 msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The miniature X‐ray emission spectrometer (miniXES) methodology will help encourage the adoption and broad application of high‐resolution XES capabilities at hard X‐ray synchrotron facilities.     

Yield analysis of large‐area high‐power single‐chip GaN‐based light‐emitting diodes with network design

In this Letter, a GaN‐based high‐power (HP) single‐chip (SC) large‐area LED with parallel and series network structure is fabricated. The optical characteristics of the HP‐SC LED is investigated. Driven at 600 mA, the optical output power of the HP‐SC LED chip is measured to be 9.7 W, corresponding to an EQE of 26.4%, which is 19.6% lower than that of the standard small LED cell due to both the lateral light‐extraction efficiency degradation and the self‐heating effect. A statistical analysis was carried out to investigate the yield of the fabricated HP‐SC LEDs, the experimental results agree with the theoretical calculations very well, validating the feasibility of this design on the production yield for the large‐area LEDs.

     

Beamline AR‐NW12A: high‐throughput beamline for macromolecular crystallography at the Photon Factory

AR‐NW12A is an in‐vacuum undulator beamline optimized for high‐throughput macromolecular crystallography experiments as one of the five macromolecular crystallography (MX) beamlines at the Photon Factory. This report provides details of the beamline design, covering its optical specifications, hardware set‐up, control software, and the latest developments for MX experiments. The experimental environment presents state‐of‐the‐art instrumentation for high‐throughput projects with a high‐precision goniometer with an adaptable goniometer head, and a UV‐light sample visualization system. Combined with an efficient automounting robot modified from the SSRL SAM system, a remote control system enables fully automated and remote‐access X‐ray diffraction experiments.     

A twelve‐analyzer detector system for high‐resolution powder diffraction

A dedicated high‐resolution high‐throughput X‐ray powder diffraction beamline has been constructed at the Advanced Photon Source (APS). In order to achieve the goals of both high resolution and high throughput in a powder instrument, a multi‐analyzer detector system is required. The design and performance of the 12‐analyzer detector system installed on the powder diffractometer at the 11‐BM beamline of APS are presented.     

Single‐cell resolution in high‐resolution synchrotron X‐ray CT imaging with gold nanoparticles

Gold nanoparticles are excellent intracellular markers in X‐ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron‐based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single‐cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 10⁵ C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X‐ray CT followed by a local tomography technique based on synchrotron X‐ray absorption yielding single‐cell resolution. The reconstructed synchrotron X‐ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections.     

Development of new CdZnTe detectors for room‐temperature high‐flux radiation measurements

Recently, CdZnTe (CZT) detectors have been widely proposed and developed for room‐temperature X‐ray spectroscopy even at high fluxes, and great efforts have been made on both the device and the crystal growth technologies. In this work, the performance of new travelling‐heater‐method (THM)‐grown CZT detectors, recently developed at IMEM‐CNR Parma, Italy, is presented. Thick planar detectors (3 mm thick) with gold electroless contacts were realised, with a planar cathode covering the detector surface (4.1 mm × 4.1 mm) and a central anode (2 mm × 2 mm) surrounded by a guard‐ring electrode. The detectors, characterized by low leakage currents at room temperature (4.7 nA cm^?2 at 1000 V cm^?1), allow good room‐temperature operation even at high bias voltages (>7000 V cm^?1). At low rates (200 counts s^?1), the detectors exhibit an energy resolution around 4% FWHM at 59.5 keV (²⁴¹Am source) up to 2200 V, by using commercial front‐end electronics (A250F/NF charge‐sensitive preamplifier, Amptek, USA; nominal equivalent noise charge of 100 electrons RMS). At high rates (1 Mcounts s^?1), the detectors, coupled to a custom‐designed digital pulse processing electronics developed at DiFC of University of Palermo (Italy), show low spectroscopic degradations: energy resolution values of 8% and 9.7% FWHM at 59.5 keV (²⁴¹Am source) were measured, with throughputs of 0.4% and 60% at 1 Mcounts s^?1, respectively. An energy resolution of 7.7% FWHM at 122.1 keV (⁵⁷Co source) with a throughput of 50% was obtained at 550 kcounts s^?1 (energy resolution of 3.2% at low rate). These activities are in the framework of an Italian research project on the development of energy‐resolved photon‐counting systems for high‐flux energy‐resolved X‐ray imaging.     

Large‐surface‐area diamond (111) crystal plates for applications in high‐heat‐load wavefront‐preserving X‐ray crystal optics

Fabrication and results of high‐resolution X‐ray topography characterization of diamond single‐crystal plates with large surface area (10 mm × 10 mm) and (111) crystal surface orientation for applications in high‐heat‐load X‐ray crystal optics are reported. The plates were fabricated by laser‐cutting of the (111) facets of diamond crystals grown using high‐pressure high‐temperature methods. The intrinsic crystal quality of a selected 3 mm × 7 mm crystal region of one of the studied samples was found to be suitable for applications in wavefront‐preserving high‐heat‐load crystal optics. Wavefront characterization was performed using sequential X‐ray diffraction topography in the pseudo plane wave configuration and data analysis using rocking‐curve topography. The variations of the rocking‐curve width and peak position measured with a spatial resolution of 13 µm × 13 µm over the selected region were found to be less than 1 µrad.     

高精度(Δ90°≤0.5″)长方体的制造技术

高精度(Δ90°≤0.5″)长方体的制造技术主要包括了加工方法和检测方法两个方面,即长方体的前期加工阶段采用立方体(方砖)形式加工,以保证一个直角的精度;后期是采用分离器单块精抛的加工方式,以保证其平行差。加工过程中用Φ150激光平面干涉仪检测和控制面形及平行度,用LY Φ80棱镜干涉仪检测和控制直角精度。这种制造技术可以将长方体的直角精度做到Δ90°≤0 5″。     

High‐throughput synchrotron X‐ray diffraction for combinatorial phase mapping

Discovery of new materials drives the deployment of new technologies. Complex technological requirements demand precisely tailored material functionalities, and materials scientists are driven to search for these new materials in compositionally complex and often non‐equilibrium spaces containing three, four or more elements. The phase behavior of these high‐order composition spaces is mostly unknown and unexplored. High‐throughput methods can offer strategies for efficiently searching complex and multi‐dimensional material genomes for these much needed new materials and can also suggest a processing pathway for synthesizing them. However, high‐throughput structural characterization is still relatively under‐developed for rapid material discovery. Here, a synchrotron X‐ray diffraction and fluorescence experiment for rapid measurement of both X‐ray powder patterns and compositions for an array of samples in a material library is presented. The experiment is capable of measuring more than 5000 samples per day, as demonstrated by the acquisition of high‐quality powder patterns in a bismuth–vanadium–iron oxide composition library. A detailed discussion of the scattering geometry and its ability to be tailored for different material systems is provided, with specific attention given to the characterization of fiber textured thin films. The described prototype facility is capable of meeting the structural characterization needs for the first generation of high‐throughput material genomic searches.     

Equation‐of‐state studies of high‐energy‐density matter using intense ion beams at the Facility for Antiprotons and Ion Research

This paper describes an experiment design based on numerical simulations to measure the equation‐of‐state properties of high‐energy‐density (HED) matter using intense particle beams. The simulations are performed using a 2D hydrodynamic computer code, BIG2, while the beam parameters are considered to match the Facility for Antiprotons and Ion Research beam. This study has shown that in such experiments one can generate different phases of HED lead. Similar calculations are planned for other materials.     

Einstein Lecture – Passion for precision

Optical frequency combs from mode‐locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective.