Deming Shu

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.

A hard X-ray nanoprobe beamline for nanoscale microscopy

The Hard X-ray Nanoprobe Beamline is a precision platform for scanning probe and full-field microscopy with 3–30 keV X-rays. A combination of high-stability X-ray optics and precision motion sensing and control enables detailed studies of the internal features of samples with resolutions approaching 30 nm.

Two dimensional hard x-ray nanofocusing with crossed multilayer Laue lenses

Hard x-ray microscopy with nanometer resolution will open frontiers in the study of materials and devices, environmental sciences, and life sciences by utilizing the unique characterization capabilities of x-rays. Here we report two-dimensional nanofocusing by multilayer Laue lenses (MLLs), a type of diffractive optics that is in principle capable of focusing x-rays to 1 nm. We demonstrate focusing to a 25 × 27 nm(2) FWHM spot with an efficiency of 2% at a photon energy of 12 keV, and to a 25 × 40 nm(2) FWHM spot with an efficiency of 17% at a photon energy of 19.5 keV.

Scanning x‐ray microscope with 75‐nm resolution

A scanning soft x‐ray microscope has been built and operated at the National Synchrotron Light Source. It makes use of a mini‐undulator as a bright source of 3.2‐nm photons. An electron beam fabricated Fresnel zone plate focuses the beam onto the specimen, which is scanned under computer control. The scanning stage can be moved by both piezoelectric transducers and stepping motors, and the location is monitored by a high‐speed laser interferometer. X rays transmitted through the specimen are detected using a flow proportional counter. Images of biological specimens and of artificial microstructures have been made with resolution in the 75–100‐nm range. Acquisition time for 256×256‐pixel images is about 5 min.

Determining metal ion distributions using resonant scattering at very high-energy K-edges:Bi/Pb in Pb5Bi6Se14

Powder diffraction data collected at ∼86 keV, and just below both the Pb and the Bi K-edges, on an imaging plate detector using synchrotron radiation from the Advanced Photon Source have been used to examine the Pb/Bi distribution over the 11 crystallographically distinct sites in Pb 5 Bi 6 Se 14 [space group P2 1 /m, a = 16.0096 (2) A, b = 4.20148 (4) A, c= 21.5689 (3) A and β = 97.537 (1)°]. The scattering factors needed for the analyses were determined both by Kramers-Kronig transformation of absorption spectra and by analyses of diffraction patterns from reference compounds. Even with the relatively low scattering contrast that is available at the K-edges, it was possible to determine the Pb/Bi distribution and probe the presence of cation site vacancies in the material. The current results indicate that resonant scattering measurements at high-energy K-edges are a viable, and perhaps preferable, route to site occupancies when absorption from the sample or sample environment/container is a major barrier to the acquisition of high-quality resonant scattering data at lower-energy edges.

High flux photon beam monitor

Abstract We have designed two photon beam position monitors for use on our X-ray storage ring beamlines. In both designs, a pair of tungsten blades, separated by a predetermined gap, intercepts a small fraction of the incoming beam. Due to photoemission, an electrical signal is generated which is proportional to the amount of beam intercepted. The thermal load deposited in the blade is transferred by a heat pipe to a heat exchanger outside the vacuum chamber. A prototype monitor with gap adjustment capability was fabricated and tested at a UV beamline. The results show that the generated electrical signal is a good measurement of the photon beam position. In the following sections, design features and test results are discussed.

Nanoscale 3D imaging at the Advanced Photon Source

Over the past decade, technology breakthroughs in the field of x-ray optics have enabled the development of advanced imaging nanoprobes at third-generation synchrotrons.1–11 X-rays have unique capabilities in terms of resolution, sensitivity, and speed, and by combining these properties with their ability to penetrate matter, these new instruments have played an important role in the recent advent of nano-material-related research.12 The gap— in terms of spatial resolution—between such x-ray instruments and electron microscopes, however, still needs to be reduced. In addition, it remains a challenge to offer in situ measurement capabilities while simultaneously pushing the spatial resolution limits. Conceptually, transmission x-ray microscopes (TXMs) are similar to optical visible light microscopes. In these instruments, tunable monochromatic x-rays illuminate the condenser—either an ellipsoidal glass mono-capillary or special type of diffraction grating known as a beam-shaping condenser (BSC)—and a Fresnel zone plate (FZP) is used as the objective lens to magnify the images or radiographs (see Figure 1). TXMs are also full-field imaging instruments, meaning that the snapshot images of absorption contrasts inside samples are acquired with 2D detectors (commonly four megapixel sensors). It is this type of full-field imaging—much faster than raster scan modes of pencil beam nanoprobes—which makes dynamic studies possible. To take on the challenge of nano-materials science in the fields of energy storage, microelectronics, nano-porous material functions, as well as life, Earth, and environmental sciences, we have developed a new in-house TXM at the Advanced Photon Source (sector 32-ID) of the Argonne National Laboratory. This instrument has replaced an older, first-generation commercial system,13 by providing a superior analytical imaging performance and in situ capabilities. In addition, our TXM supports a Figure 1. (a) Schematic representation of a transmission x-ray microscope (TXM) used for nano-tomography studies. (b) Photograph of the TXM that has been developed at sector 32-ID of the Argonne National Laboratory’s Advanced Photon Source. -CT: Micro-computed tomography.

Soft‐x‐ray imaging with the 35 period undulator at the NSLS

In the summer of 1988, the National Synchrotron Light Source installed a 35 period soft‐x‐ray undulator. We are using this device as a radiation source for a beamline designed for soft‐x‐ray imaging experiments that require high brightness for practical operation. We present the design philosophy and implementation of this beamline. Preliminary characterization of the beamline and undulator indicate that the central intensity of the undulator is within a factor of 2 of design. We have measured an intensity of more than 1015 photons/s/0.1% BW/mrad2 at 36 A. The monochromator has achieved its design resolving power of 2000.

A high-fidelity harmonic drive model.

In this paper, a new model of the harmonic drive transmission is presented. The purpose of this work is to better understand the transmission hysteresis behavior while constructing a new type of comprehensive harmonic drive model. The four dominant aspects of harmonic drive behavior - nonlinear viscous friction, nonlinear stiffness, hysteresis, and kinematic error - are all included in the model. The harmonic drive is taken to be a black box, and a dynamometer is used to observe the input/output relations of the transmission. This phenomenological approach does not require any specific knowledge of the internal kinematics. In a novel application, the Maxwell resistive-capacitor hysteresis model is applied to the harmonic drive. In this model, sets of linear stiffness elements in series with Coulomb friction elements are arranged in parallel to capture the hysteresis behavior of the transmission. The causal hysteresis model is combined with nonlinear viscous friction and spectral kinematic error models to accurately represent the harmonic drive behavior. Empirical measurements are presented to quantify all four aspects of the transmission behavior. These measurements motivate the formulation of the complete model. Simulation results are then compared to additional measurements of the harmonic drive performance.

THE SCANNING TRANSMISSION MICROSCOPE AT THE NSLS

Abstract The scanning transmission soft X-ray microscope (STXM) that has been under development at the National Synchrotron Light Source [H. Rarback et al., Rev. Sci. Instr. 59 (1988) 52] has been substantially ungraded for operation with the X1 undulator [C. Buckley et al., Rev. Sci. Instr. 60 (1989) 2444]. The principal new features are: optical prefocusing, using a visible light interferometer; a dedicated VAXstation 3200 with a more user friendly and flexible software system for image acquisition and analysis; a flow cell that makes it possible not only to keep the specimen wet during exposure, but to change the fluid around the specimen as well; and a more compact proportional counter that is capable of counting rates of several MHz. In conjunction with new zone plates of better resolution and higher efficiency [E.H. Anderson, SPIE 1160 (1989) 2], the microscope is ready for a period of extended use in biological imaging.