Applications of Superconducting Detectors
Some of the most energetic objects and phenomenon in the universe are strong x-ray sources. Accretion discs of black holes emit x-rays, as do quasars, galactic clusters, and supernova remnants. Studies of these objects are limited by the performance of current x-ray spectrometers. To observe x-rays large grazing-incidence telescopes must be launched into space. Superconducting detectors provides the solution to many of these problems. The detectors have high resolution and, with the appropriate x-ray absorber, can have near 100% quantum efficiency over a large bandwidth (few eV to >100 keV). Conventional crystal spectrometers do not have enough sensitivity to study most objects with even the largest x-ray telescopes under development (Constellation X). Conventional semiconductor detectors have very good sensitivity, but lack the necessary spectral resolution.
We use x-rays generated by synchrotron emission for two purposes. First, we use low-flux beam lines to characterize the performance of our detectors. Second, we use high-flux beam lines to study materials and biological processes. We performed demonstration experiments using our Superconducting Tunnel Junctions (STJ's) at the Stanford Synchrotron Radiation Laboratory. X-ray fluorescence of various elements were observed and measured. With the high energy resolution of our detectors, we were able to distinguish between elements whose emission lines were very close together. For example, our detectors were able to sense small traces of titanium. Using current state-of-the-art semiconductor detectors, the titanium lines would be obscured by neighboring nitrogen and oxygen lines.
In the semiconductor industry, the level of contamination in the devices is crucial to its quality. Currently, contaminents are found by scanning wafers with an electron or x-ray beam and looking for flourescence of undesired elements. But as feature sizes decrease, x-ray and electron beams will damage the microstructures. Inspection for contamination would have to be performed with very low energy x-rays. The flouresced x-rays will have even lower energies. We have optimized our detectors for low-energy x-ray detection already. Our technology is best suited for this sort of application.
UCRL-MI-141695