Showing papers by "Howard A. Padmore published in 1996"

Soft x-ray spectromicroscopy development for materials science at the Advanced Light Source

Abstract: Several third generation synchrotron radiation facilities are now operational and the high brightness of these photon sources offers new opportunities for x-ray microscopy. Well developed synchrotron radiation spectroscopy techniques are being applied in new instruments capable of imaging the surface of a material with a spatial resolution smaller than one micron. There are two aspects to this. One is to further the field of surface science by exploring the effects of spatial variations across a surface on a scale not previously accessible to x-ray measurements. The other is to open up new analytical techniques in materials science using x-rays, on a spatial scale comparable to that of the processes or devices to be studied. The development of the spectromicroscopy program at the Advanced Light Source will employ a variety of instruments, some are already operational. Their development and use will be discussed, and recent results will be presented to illustrate their capabilities.

New schemes for producing high-accuracy elliptical x-ray mirrors by elastic bending

Abstract: Although x-ray micro-foci can be produced by a variety of diffractive methods, grazing incidence mirrors are the only route to an achromatic focus. In this paper we describe our efforts to produce elliptically shaped mirrors with the very high figure accuracy necessary for producing a micro-focus. The motivation for this work is provided by the need to produce achromatic foci for a range of applications ranging from tunable micro-focus x-ray photoelectron spectroscopy ((mu) -XPS) at soft x-ray energies to micro-focus white beam x-ray diffraction ((mu) -XRD) at hard x-ray energies. We describe the methodology of beam bending, a practical example of a system we have produced for (mu) -XRD, and results demonstrating the production of a surface with micro-radian figure accuracy.

Design and performance of the ALS diagnostic beamline

Abstract: The design and operation of an imaging beamline at the Advanced Light Source used for providing diagnostic information on the electron beam for the accelerator and experimental groups is described. This system is based on a Kirkpatrick‐Baez mirror pair and utilizes a carbon filter to give a bandpass in the soft x‐ray region. The focused x‐rays are viewed on a single‐crystal scintillator through an optical microscope and the image recorded on a CCD camera. This system, together with other instruments to evaluate beam size, stability, and other time‐dependent information, is described, data are presented, and the operation of the overall beamline is evaluated.

Two-dimensional Pixel Array Image Sensor for Protein Crystallography

Abstract: A 2D pixel array image sensor module has been designed for time resolved Protein Crystallography. This smart pixels detector significantly enhances time resolved Laue Protein crystallography by two to three orders of magnitude compared to existing sensors like films or phosphor screens coupled to CCDs. The resolution in time and dynamic range of this type of detector will allow one to study the evolution of structural changes that occur within the protein as a function of time. This detector will also considerably accelerate data collection in static Laue or monochromatic crystallography and make better use of the intense beam delivered by synchrotron light sources. The event driven pixel array detectors, based on the column Architecture, can provide multiparameter information (energy discrimination, time), with sparse and frameless readout without significant dead time. The prototype module consists of a 16x16 pixel diode array bump-bonded to the integrated circuit. The detection area is 150x150 square microns.

Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation

Abstract: Using multilayer linear polarizers, we have studied the polarization state of radiation from bend magnet beamline 9.3.2 at Advanced Light Source as function of vertical oping angle at photon energies 367 and 722 eV. Both a fine slit and a coarse semi-aperture were stepped across the beam to accept different parts of the vertical radiation fan. Polarimetry yields the degree of linear polarization directly and the degree of circular polarization indirectly assuming an immeasurably small amount of unpolarized radiation based on close agreement of theory and experiment for linear polarization. Results are in good agreement with theoretical calculations, with departures from theory owing to uncertainty in effective aperture of the measured beam. The narrow 0.037 mrad aperture on the orbit plane transmits a beam whose degree of linear polarization exceeds 0.99 at these energies. The wide semi-aperture blocking the beam from above and below transmits a beam with a max figure of merit, given by the square root of flux times degree of circular polarization, when the aperture edge is on the orbit plane thus blocking only half of the total available flux.

Elliptically polarizing undulator beamline 4.0.1 for magnetic spectroscopy at the Advanced Light Source

Abstract: A beamline for high resolution spectroscopy with elliptically polarized X-rays is described.The working energy range is large, from 20 eV to above 1800 eV. The resolving power is on the order of 10,000 at low energies (20-200 eV) and 6000 at high energies (200-1800 eV). This is achieved using a variable deviation angle plane grating monochromator. A single grating, with one line density and a varying groove depth, is used to cover the entire energy range. The beamline has been designed to operate with either one or two x-ray beams propagating simultaneously through the monochromator and to the experimental station. Switching between polarizations at rates of 0.1 Hz and slower is accomplished in the single beam mode by alternating the output of the elliptically polarized undulator source between left and right polarization. Fast polarization switching, at rates of 100-1000 Hz, is provided in the two beam mode by mechanical chopping between two photon beams, one of which is right circularly polarized, and the other left circularly polarized.

A 2D smart pixel detector for time‐resolved crystallography

Abstract: A smart pixel detector is being developed for time‐resolved crystallography for biological and material science applications. Using the pixel detector presented here, the Laue method will enable the study of the evolution of structural changes that occur within a protein as a function of time. The x‐ray pixellated detector is assembled to the integrated circuit through a bump bonding process. Within a pixel size of 150×150 mm2, a low‐noise preamplifier‐shaper, a discriminator, a 3‐bit counter and the readout logic are integrated. The readout, based on the column architecture principle, will accept hit rates above 5×108/cm2/s with a maximum hit rate per pixel of 1 MHz. This detector will allow time‐resolved Laue crystallography to be performed in a frameless operation mode, without dead time. Target specifications, architecture, and preliminary results on a 8×8 prototype are presented.

Total reflection X-ray fluorescence spectroscopy using synchrotron radiation for trace impurity analysis of silicon wafer surfaces

Abstract: One of the principal industry standard means of measuring surface and near surface wafer contamination is the total reflection X-ray fluorescence (TXRF). A TXRF experiment using synchrotron radiation is carried out at the Advance light source (ALS) beamline 10.32 to investigate the performance of synchrotron radiation based approaches for this application. The detection limit of 4.9×109 atoms/cm2 is achievable for the 3-d elements with the present ALS TXRF beamline 10.32. This is due to the greatly improved signal to background in case of the synchrotron radiation TXRF. Furthermore, there is a path to improving the synchrotron case to reach a detection limit of 7.8 × 107 atoms/cm2.

An elliptical wiggler beamline for the ALS

Abstract: A beamline for circularly polarized radiation produced by an elliptical wiggler has been designed at the ALS covering the broad energy range from 50 eV to 2000 eV. The rigorous theory of grating diffraction efficiency has been used to maximize transmitted flux. The nature of the elliptical wiggler insertion device creates a challenging optical problem due to the large source size in the vertical and horizontal directions. The requirement of high resolving power, combined with the broad tuning range and high heat loads complicate the design. These problems have been solved by using a variable included angle monochromator of the ``constant length`` type with high demagnification onto its entrance slit, and cooled optics.

Production and Characterization of Circularly Polarized Soft X-Rays for Materials Research at the ALS

Abstract: The experimental program at the Advanced Light Source to produce and characterize circularly polarized x-rays is described. A number of beamlines are either operating or under construction which produce circularly polarized light. Bend magnets, multilayer phase retarders, and insertion devices which directly produce circularly polarized radiation are described. These beamlines will have capabilities for both microscopy and high resolution spectroscopy. Measurements of the linear and circular polarization of these beamlines are also described.