The Absorbance Spectroscopy effort seeks to develop measurements that provide details of the local chemical, electronic, and physical structure in advanced materials. Spectrometer technology is developed as part of the NIST BNL partnership at the National Synchrotron Light Source II in Upton, NY. Specific goals of the project are to develop detector technologies with higher speed and higher sensitivity to achieve greater measurement capability, reliability, and information content. These efforts are complemented by the development of automated sample environments, higher throughput data processing, robust reduction and modelling platforms, and testing within a wide range of NIST projects and programs as well as the general user program at NSLS-II.
Of the nine end stations in designed and operated by NIST, four are dedicated for various applications of X-ray absorbance spectroscopy. After exposing a sample to an incident X-ray beam, the excitation and resulting decay process of electrons are measured. The energy of the emitted electron is the excitation energy of the shell from which it originated. The use of a synchrotron source adds three primary capabilities to lab-based analogs. First, the source brilliance allows the development of highly focused beams and measure at high throughputs. This results in key abilities to measure samples beyond spatially uniform films, and has been essential in the NIST effort to characterized devices in the semiconductor industry, combinatorial material arrays, and process uniformity. The second advantage is the capacity to tune the energy of the incident beam. For measurements such as Hard X-ray Photoelectron Spectroscopy (HAXPES), this feature provides a depth dependent version of XPS not feasible without this tunability.
Detector development is highlighted on the Soft X-ray Absorption and Emission Spectrometer (μCAL), which has an acronym based on the detector itself. The microcalorimeter detection system has been developed for this application in collaboration with the NIST Quantum Sensors Group. The detector is tuned to a superconducting-to-normal-metal transition, with a cascading effect on conductivity as single photons provide small amounts of heat. This state of the art, 1 eV resolution detector has been adopted recently at the Stanford Linear Accelerator Complex (SLAC) for a related application and continues to be of great interest across the X-ray community.