A.C. Thompson

First operation of the medical research facility at the NSLS for coronary angiography

The Synchrotron Medical Research Facility (SMERF) at the National Synchrotron Light Source has been completed and is operational for human coronary angiography experiments. The imaging system and hardware have been brought to SMERF from the Stanford Synchrotron Radiation Laboratory where prior studies were carried out. SMERF consists of a suite of rooms at the end of the high‐field superconducting wiggler X17 beam line and is classified as an Ambulatory Health Care Facility. Since October of 1990 the coronary arteries of five patients have been imaged. Continuously improving image quality has shown that a large part of both the right coronary artery and the left anterior descending coronary artery can be imaged following a venous injection of contrast agent.

Direct correlation of transition metal impurities and minority carrier recombination in multicrystalline silicon

Impurity and minority carrier lifetime distributions were studied in as-grown multicrystalline silicon used for terrestrial-based solar cells. Synchrotron-based x-ray fluorescence and the light beam induced current technique were used to measure impurity and lifetime distributions, respectively. The purpose of this work was to determine the spatial relation between transition metal impurities and minority carrier recombination in multicrystalline silicon solar cells. Our results reveal a direct correlation between chromium, iron, and nickel impurity precipitates with regions of high minority carrier recombination. The impurity concentration was typically 5×1016 atoms/cm2, indicating the impurity-rich regions possess nanometer-scale precipitates. These results provide the first direct evidence that transition metal agglomerates play a significant role in solar cell performance.

Nanometer-scale metal precipitates in multicrystalline silicon solar cells

In this study, we have utilized characterization methods to identify the nature of metal impurityprecipitates in low performance regions of multicrystalline silicon solar cells. Specifically, we ha ...

X-ray beam induced current—a synchrotron radiation based technique for the in situ analysis of recombination properties and chemical nature of metal clusters in silicon

A synchrotron radiation based x-ray microprobe analytical technique, x-ray beam induced current (XBIC), is suggested and demonstrated at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The principle of XBIC is similar to that of electron/laser beam induced current with the difference that minority carriers are generated by a focused x-ray beam. XBIC can be combined with any other x-ray microprobe tool, such as the x-ray fluorescence microprobe (μ-XRF), to complement chemical information with data on the recombination activity of impurities and defects. Since the XBIC signal, which carries information about the recombination activity of defects in the sample, and the μ-XRF signal, which contains data on their chemical nature, can be collected simultaneously, this combination offers a unique analytical capability of in situ analysis of the recombination activity of defects and their chemical origin with a high sensitivity and a micron-scale spatial resolution. Examples of an applicat...

Elemental measurements with an X-ray microprobe of biological and geological samples with femtogram sensitivity

Abstract An X-ray microprobe has been developed to measure the concentration and spatial distribution of many elements quickly and simultaneously with a beam spot size of less than 10 μm × 10 μm. This instrument uses a pair of multilayer coated concave spherical mirrors arranged in the Kirkpatrick-Baez geometry to focus the beam. The fluorescent X-rays from the sample are detected with a Si(Li) detector. Samples are scanned in a raster manner to create one- or two-dimensional maps of elemental concentrations. Since samples are not under vacuum, a wide variety of samples can be scanned. Femtogram sensitivities for trace elements from K to Zn can be achieved in a 60 s counting time.

Computed tomography with monochromatic X-rays from the National Synchrotron Light Source

Abstract A multiple-energy computed tomography (MECT) system that employs monochromatic and tunable 33–100 keV X rays from a superconducting wiggler at the National Synchrotron Light Source is being developed at Brookhaven National Laboratory. The CT configuration is that of a fixed, horizontal fan-shape beam and a subject seated in a rotating chair. Two quantitative CT methods will be used: a) K-edge subtraction of intravenously administered iodine (or a heavier element) to image brain tumors, large blood vessels of the lower head and neck, and arteriovenous malformations; and b) dual photon absorptiometry to obtain two brain CT images that map the low−Z elements and the intermediate−Z elements (i.e. P, S, Cl, K, Ca, and Fe) separately. The system is expected to provide 0.5 mm spatial resolution, horizontally, with unprecedented image contrast and accuracy of quantification. The system will employ a two-crystal monochromator and a high-purity Ge linear array detector.

Transvenous coronary angiography using synchrotron radiation

X-ray-based angiography continues to be the standard method of assessing the severity and the extent of coronary atherosclerosis. The relative insensitivity of conventional X-ray imaging systems to iodine-containing contrast agents necessitates that the images be acquired with essentially undiluted contrast agent in the lumen of the vessels being studied. This, in turn, requires arterial catheterization and the insertion of the catheter tip in or near the ostia of the vessels and the direct injection of the contrast agent. The health risks and monetary costs of the procedure have limited its use to circumstances in which there is a high probability of the presence of severe disease. Despite these problems, coronary angiography has been employed in serial studies to evaluate the effects of drug therapy and diet on coronary atherosclerosis (1).

Coronary angiography using synchrotron radiation (invited)

Imaging of coronary arteries using a venous instead of an arterial injection of contrast agent could provide a much safer method to diagnose heart disease. The tunability, intensity, and collimation of synchrotron radiation x‐ray beams makes possible imaging systems with greatly improved imaging sensitivity. A pair of fan x‐ray beams, a movable patient chair, and a multielement x‐ray detector are used to acquire a pair of x‐ray images above and below the iodine K edge. The logarithmic subtraction of these two images produces an image with excellent sensitivity to contrast agent and minimal sensitivity to bone and tissue. High‐quality images from a dog and preliminary images from five humans have been obtained. Improvements are being made to the system to increase the effective radiation flux and to measure the position of both x‐ray beams.

A tunable x-ray microprobe using synchrotron radiation

Abstract We describe an X-ray microprobe using multilayer mirrors. Previously, we have demonstrated a Kirkpatrick-Baez type focusing system working at both 8 and 10 keV and successfully applied it to a variety of applications, including the determination of elemental contents in fluid inclusions. In this paper, we show that the usable excitation energy for this microprobe is not restricted to between 8 and 10 keV, and furthermore that it can be simply tuned in operation. A 10 keV X-ray fluorescence microprobe can be used to measure the concentration of the elements from K (Z = 19) to Zn (Z = 30) using K X-ray lines, and from Cd (Z = 48) to Er (Z = 68) using L X-ray lines. There are a number of geologically important elements in the gap between Ga (Z = 31) and Ag (Z = 47) and with Z > 68. In order to cover this range, a higher excitation energy is required. On the other hand, for samples that contain major elements with absorption edges lower than the excitation energy, it would be hard to detect other minor elements because of the strong signal from the major elements and the background they produce. In this case, a tunable X-ray source can be used to avoid the excitation of the major elements. We demonstrate that, with the existing setup, it is possible to tune the excitation energy from 6 to 14 keV. In this range, the intensity does not decrease by more than one order of magnitude. As an illustrative example, a geological sample was examined using two different excitation energies to show the advantage of a tunable source. Finally, we discuss the possibility of further extension of the excitation energy range as well as the possibility of improving the intensity.

Copper precipitates in silicon: Precipitation, dissolution, and chemical state

The precipitation and dissolution of copper impurities at oxygen precipitates and stacking faults in silicon were studied using thermal budgets commensurate with standard integrated circuit processing. Additionally, in order to develop a better understanding of the dissolution process, we have obtained results on the chemical state of the copper precipitates. The goal of this work was to determine the feasibility of removing and maintaining copper impurities away from the active device region of an integrated circuit device by use of oxygen precipitates and stacking faults in the bulk of the material. Based on our results, we provide a basis for a predictive understanding of copper precipitation and dissolution in silicon and we discuss the feasibility of copper impurity control in silicon integrated circuit devices.