Third-generation Synchrotron Facility Research Articles

Propagation of a partially coherent focused X-ray beam within a planar X-ray waveguide

A linear-transmission Fresnel-zone-plate lens is used for coupling a monochromatic X-ray beam of 13.2 keV into a planar X-ray waveguide. The zone plate focuses the beam parallel to the entrance of the waveguide, by which means a flux enhancement of a factor of 54 inside the waveguide is obtained. This substantially enlarges the range of X-ray diffraction experiments that can be performed on samples confined within the waveguide. The coherent properties of the beam, as obtained at a third-generation synchrotron facility, are investigated by comparing the experimental data with numerical calculations in which partial coherence is taken into account by propagation of the mutual intensity function. The conditions for which the X-rays travelling through the waveguide are coherent are discussed.

Tomography of integrated circuit interconnect with an electromigration void

An integrated circuit interconnect was subject to accelerated-life test conditions to induce an electromigration void. The silicon substrate was removed, leaving only the interconnect test structure encased in silica. We imaged the sample with 1750 eV photons using the 2-ID-B scanning transmission x-ray microscope at the Advanced Photon Source, a third-generation synchrotron facility. Fourteen views through the sample were obtained over a 170° range of angles (with a 40° gap) about a single rotation axis. Two sampled regions were selected for three-dimensional reconstruction: one of the ragged end of a wire depleted by the void, the other of the adjacent interlevel connection (or “via”). We applied two reconstruction techniques: the simultaneous iterative reconstruction technique and a Bayesian reconstruction technique, the generalized Gaussian Markov random field method. The stated uncertainties are total, with one standard deviation, which resolved the sample to 200±70 and 140±30 nm, respectively. The tungsten via is distinguished from the aluminum wire by higher absorption. Within the void, the aluminum is entirely depleted from under the tungsten via. The reconstructed data show the applicability of this technique to three-dimensional imaging of buried defects in submicrometer structures relevant to the microelectronics industry.

Performance limits of direct cryogenically cooled silicon monochromators – experimental results at the APS

The successful use of cryogenically cooled silicon monochromators at third-generation synchrotron facilities is well documented. At the Advanced Photon Source (APS) it has been shown that, at 100 mA operation with the standard APS undulator A, the cryogenically cooled silicon monochromator performs very well with minimal (<2 arcsec) or no observable thermal distortions. However, to date there has not been any systematic experimental study on the performance limits of this approach. This paper presents experimental results on the performance limits of these directly cooled crystals. The results show that if the beam is limited to the size of the radiation central cone then, at the APS, the crystal will still perform well at twice the present 100 mA single 2.4 m-long 3.3 cm-period undulator heat load. However, the performance would degrade rapidly if a much larger incident white-beam size is utilized.

In situ surface X-ray diffraction studies of electrochemical interfaces at a high-energy third-generation synchrotron facility

We have developed a new spectro-electrochemical cell derived from the three-electrodes standard cell, in order to study the electrolyte/single-crystal interfaces by using surface X-ray diffraction. Results obtained with this cell are described here. We studied the phase transition of gold (111) in sulfuric acid. Preliminary results are shown concerning the overpotential deposition and the new possibilities that are opened by the use of a 2-D X-ray-sensitive detector. This set-up allowed us to follow in situ and in real time the morphology of Cu growth on Au (001), in free and surfactant-containing solution.

Tomographic reconstruction of an integrated circuit interconnect

An Al–W-silica integrated circuit interconnect sample was thinned to several μm and scanned across a 200 nm focal spot of a Fresnel zone plate operating at photon energy of 1573 eV. The experiment was performed on beamline 2-ID-B of the Advanced Photon Source, a third-generation synchrotron facility. Thirteen scanned projections of the sample were acquired over the angular range ±69.2°. At least 301×301 pixels were acquired at each angle with a step size of 77×57 nm. A three-dimensional image with an approximate uncertainty of 400 nm was reconstructed from projection data using a standard algorithm. The two layers of the integrated circuit and the presence of the focused ion beam markers on the surface of the sample are clearly shown in the reconstruction.

Structural Studies of DNA–Cationic Lipid Complexes Confined in Lithographically Patterned Microchannel Arrays

We have used lithographically patterned microchannel arrays with channel widths ranging from 1 to 20 μm, fabricated using electron beam lithography and reactive ion etching, in structural studies of DNA–cationic lipid complexes in confinement. Various techniques have been developed for loading these DNA–membrane complexes into the microchannels or to form the complexes in situ by sequentially depositing DNA and lipid solutions into the microchannels. Optical microscopy studies indicate that such complex formation is strongly influenced by the periodic channel structure even at channel widths much larger than the persistent length of the DNA molecules. Preliminary x-ray diffraction experiments conducted at Stanford Synchrotron Radiation Laboratory (SSRL) yielded only a weak signal from the lipid bilayers in the complexes. The use of a microfocused x-ray beam produced by the newly developed Bragg–Fresnel optics at a third-generation synchrotron facility may dramatically increase the signal-to-noise ratio and allow observation of orientational as well as positional ordering of DNA molecules induced by the microchannels. Structural control of the DNA–membrane complexes has a broad range of potential applications in gene probe technology and as mesoscopic biomolecular composites.

Esca Microscopy on Elettra: Chemical Characterization of Surfaces and Interfaces With Sub-Micron Spatial Resolution

ABSTRACTThe chemical sensitivity, spatial resolution and data acquisition rates achieved with the scanning photoelectron microscope built at ELETTRA, a third-generation synchrotron facility in Italy has made it an indispensable tool for surface analysis of laterally heterogeneous materials. The information on the composition and evolution of coexisting phases, mass transport and other surface processes occurring on a microscopic scale can be obtained by combining elemental and chemical mapping with core and valence level photoelectron spectromicroscopy with spatial resolution better than 0.15 μm and energy resolution better than 0.5 eV. Selected recent results will be presented to illustrate the capabilities and some of the possible applications of synchrotron radiation spectromicroscopy for characterization of complex spatially heterogeneous materials and studies of dynamic processes related to the interface chemical structure.

High-Resolution X-ray Fluorescence and Excitation Spectroscopy of Metalloproteins

A spectrograph has been developed with sufficient efficiency to make high-resolution fluorescence experiments on metalloproteins possible. The resolution of this spectrometer can reach 0.45 eV at 7.1 keV emission energy. The focus images of this multiple curved-crystal array spectrometer are presented. The chemical sensitivity of Kbeta emission spectra can be used to identify chemical states, and the spin-polarized near-edge structure provides a new measure of the spin density. The high-resolution fluorescence metalloprotein studies should become routine with third-generation synchrotron facilities, and the strength of both site and spin selectivity should complement the structural information from other spectroscopies.

Ion beam induced surface modification of chemical vapor deposition diamond for x-ray beam position monitor applications

The Advanced Photon Source at Argonne National Laboratory is a third-generation synchrotron facility that generates powerful x-ray beams on its undulator beamlines for a variety of scientific and industrial user research programs. It is very important to know the position and the angle of the x-ray beam during experiments. Due to very high heat flux levels, several patented x-ray beam position monitors (XBPMs) exploiting beneficial characteristics of chemical vapor deposition (CVD) diamond have been developed. These XBPMs have a thin layer of low-atomic-mass metallic coating so that photoemission from the x rays generates a minute but measurable current for position determination. Another concept has been the graphitization of the CVD diamond surface to create a very thin, intrinsic conducting layer that can stand much higher temperatures and have minimal x-ray transmission losses compared to coated metallic layers. In the present study, a laboratory sputter ion source was used to transform selected surfaces of a CVD diamond substrate into graphite. The effect of 1–5 keV argon ion bombardment on CVD diamond surfaces at various target temperatures from 200 to 500 °C was studied using Auger electron spectroscopy and in situ electrical resistivity measurements. Graphitization after the ion bombardment was confirmed, and optimum conditions for graphitization were studied. Raman spectroscopy was applied to identify the overall diamond structure in the bulk of CVD diamond substrate after the ion bombardments. It was found that the target temperature plays an important role in the stability and electrical conductivity of the irradiated CVD diamonds.

In-situ long trace profiler for measurement of mirror profiles at third-generation synchrotron facilities (abstract)

X-ray mirrors have the potential to be subjected to extremely high heat loads at third-generation synchrotron radiation sources. In many cases, sophisticated cooling methods will be required to prevent surface distortion that would otherwise degrade the intrinsic source brightness. As a diagnostic for such mirrors, we have previously proposed to modify the long trace optical profiler for use within a UHV mirror chamber [Shinan Qian et al., Optical Engineering 34, 396 (1995)], thereby making it feasible to take profile measurements of mirrors irradiated with high power x-ray beams. We present in detail the mechanical design of a complete in-situ measurement. The objective of developing an in-situ measurement system is to aid the development of reliable, low-cost, high-heat-load substrates for mirrors and multilayers. This will provide a firm basis on which to design new optical elements that will be necessary as a result of performance enhancements to current machines, as well as future generations of storage rings.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keVa)

Interest in the 0.5 to 3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition-metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5-cm-period, planar undulator to be installed on the 7-GeV Advanced Photon Source will produce a high brightness source of intermediate-energy x rays. The 0.5- to 3-keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft-x-ray region, below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression, will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described.

Spectroscopy beamline at the Advanced Photon Source for the photon energy region from 0.5 to 3 keV (abstract)

Interest in the 0.5–3 keV, intermediate x-ray, energy region has recently intensified as this spectral region covers, among others, the important L and M edges of transition metal and rare-earth magnetic materials, respectively. Third-generation synchrotron facilities with their inherent high brightness have the unique potential to cover this energy region with high-resolution, high-flux x-ray beams ideal for spectroscopic studies. A 5.5 cm period, planar undulator to be installed on the 7 GeV Advanced Photon Source will produce a high brightness source of intermediate energy x-rays. The 0.5–3 keV spectroscopy beamline is based on the spherical grating monochromator design that has already been shown to yield high resolution and throughput in the soft x-ray region below 1 keV. The beamline has been designed to cover the entire region with a peak resolving power of 6000–10 000. Photon flux at the sample is calculated to be in the range from 1011 to 1013 photons/s into a spot size of 1 mm2. A refocusing mirror will be used to further demagnify the image size at a second experimental station. As a second phase to the spectroscopy program, an elliptically polarized insertion device will be used. The polarization preserving nature of the grazing incidence optical elements in the SGM is crucial to obtain x rays of well-defined polarization. The beamline layout, together with calculations of resolution, throughput, power loading, and high harmonic suppression will be presented. The photoemission experimental end stations for the spectroscopy station will also be briefly described. This research was supported by the U.S. Department of Energy, BES Materials Sciences under Contract No. W-31-109-ENG-38.

Taking stock: performance and prospects

Taking stock: performance and prospects