A High-Performance Superconducting Tunnel Junction (STJ) Soft X-ray Detector for Biological Science.

A major limiting factor for biological soft X-ray absorption spectroscopy (XAS) is the capability of the available X-ray fluorescence detectors. There is an enormous and largely untapped potential for biological soft (XAS) at synchrotron light sources, as the metal L-edge and light element K- edge transitions in this region often reveal element-specific chemical details that cannot be readily obtained in other ways. Other technical issues, such as the need for high vacuum, inherently short pathlengths, difficulties in preparing suitable samples and radiation damage, have been solved over the past few years. We propose to develop a next-generation, high performance, soft X-ray detector based on novel, single-tunneling Ta-AlOx-Nb-Au superconducting tunnel junctions (STJs), a technology which offers orders of magnitude improved count-rates and improved inherent energy resolution. In order to improve the collection efficiency, we will couple this detector with an axially symmetric X-ray optic. The resulting detector will achieve each of the high count-rate, the high energy resolution, and the X-ray collection efficiency needed when working with dilute, X-ray sensitive materials such as biological systems. We will demonstrate that we can construct test Ta-AlOx-Nb-Au STJ chips. These will then be tested at LLNL as potential high-speed, high energy resolution X-ray detectors. We will also investigate Nb-STJs as an alternative route for high-speed devices. We will also demonstrate use of a focusing cylindrical optic to enhance STJ array collection efficiency. Single-tunneling Ta-AlOx-Nb-Au STJs, together with the option of a focusing optic, will greatly enhance the X-ray spectrometers that we offer for synchrotron science and X-ray microscopy applications. These novel STJs will increase instrumental sensitivity for diverse applications such as particle contaminations on microchips and dopant chemistry in novel materials.