David A. Wollman

High‐resolution, energy‐dispersive microcalorimeter spectrometer for X‐ray microanalysis

We have developed a prototype X‐ray microcalorimeter spectrometer with high energy resolution for use in X‐ray microanalysis. The microcalorimeter spectrometer system consists of a superconducting transition‐edge sensor X‐ray microcalorimeter cooled to an operating temperature near 100 mK by a compact adiabatic demagnetization refrigerator, a superconducting quantum interference device current amplifier followed by pulse‐shaping amplifiers and pileup rejection circuitry, and a multichannel analyser with computer interface for the real‐time acquisition of X‐ray spectra. With the spectrometer mounted on a scanning electron microscope, we have achieved an instrument response energy resolution of better than 10 eV full width at half‐maximum (FWHM) over a broad energy range at real‐time output count rates up to 150 s−1. Careful analysis of digitized X‐ray pulses yields an instrument‐response energy resolution of 7.2 ± 0.4 eV FWHM at 5.89 keV for Mn Kα1,2 X‐rays from a radioactive 55Fe source, the best reported energy resolution for any energy‐dispersive detector.

X-ray Detection Using a Superconducting Transition-edge Sensor Microcalorimeter with Electrothermal Feedback

We have developed a new type of x‐ray detector based on a superconducting transition‐edge thermometer operated near 100 mK. A superconducting quantum interference device is used to measure the current through the thermometer, and negative electrothermal feedback is used to improve the energy resolution and shorten the thermal time constant. We have used a detector mounted on a scanning electron microscope to measure the energy of titanium Kα (4.5 keV) fluorescence x rays with a resolution better than 14 eV full width at half‐maximum. Using two other devices, we have measured an energy resolution for Joule heat pulses of 2.6 eV at 1 keV and 0.2 eV at 4 eV, the best reported for any calorimeter. An electrical noise equivalent power of 3×10−18 W/√Hz was also measured, suggesting the use of these detectors as infrared bolometers.

Thermal-response time of superconducting transition-edge microcalorimeters

We investigate limits on the thermal-response time of superconducting transition-edge microcalorimeters. For operation at 0.1 K, we show that the lower limit on the response time of a superconducting transition-edge microcalorimeter is of order 1 μs due to the heat diffusion time, electrical instabilities, the amplifier noise, and the critical current of the superconducting film. The response time is not limited by self-heating effects and is independent of the intended photon energy. However, design constraints associated with the inductance of the bias circuit make it difficult to achieve the fastest response times for devices with heat capacities high enough for x-ray and gamma-ray detection.

Impact Energy Measurement in Time-of-Flight Mass Spectrometry with Cryogenic Microcalorimeters

Time-of-flight mass spectrometry—most notably matrix-assisted laser-desorption-ionization time-of-flight (MALDI-TOF) spectrometry—is an important class of techniques for the study of proteins and other biomolecules. Although these techniques provide excellent performance for masses up to about 20,000 daltons, there has been limited success in achieving good mass resolution at higher masses. This is because the sensitivity of the microchannel plate (MCP) detectors used in most systems decreases rapidly with increasing particle mass, limiting the utility of MCP detectors for very large masses. It has recently been proposed that cryogenic particle detectors may provide a solution to these difficulties. Cryogenic detectors measure the thermal energy deposited by the particle impact, and thus have a sensitivity that is largely independent of particle mass. Recent experiments,, have demonstrated the sensitivity of cryogenic particle detectors to single biomolecules, a quantum efficiency several orders of magnitude larger than the MCP detectors, and sensitivity to masses as large as 750,000 daltons. Here we present results demonstrating an order of magnitude better energy resolution than previous measurements, allowing direct determination of particle charge state during acceleration. Although application of these detectors to practical mass spectrometry will require further development of the detectors and cryogenics, these detectors can be used to elucidate the performance-limiting processes that occur in such systems.

Microfabricated transition-edge X-ray detectors

We are developing high performance X-ray detectors based on superconducting transition-edge sensors (TES) for application in materials analysis and astronomy. Using our recently developed fully lithographic TES fabrication process, we have made devices with an energy resolution of 4.5/spl plusmn/0.1 eV for 5.9 keV X-rays, the best reported energy resolution for any energy dispersive detectors in this energy range. These detectors utilize micromachined thermal isolation structures and transition-edge sensors fabricated from Mo/Cu bilayers with normal-metal boundary conditions. We have found the normal-metal boundary conditions to be critical to stable and reproducible low noise operation. In this paper we present details of fabrication and performance of these devices.

Calculation of TC in a normal-superconductor bilayer using the microscopic-based Usadel theory

Abstract The Usadel equations give a theory of superconductivity, valid in the diffusive limit, that is a generalization of the microscopic equations of the BCS theory. Because the theory is expressed in a tractable and physical form, even experimentalists can analytically and numerically calculate detailed properties of superconductors in physically relevant geometries. Here, we describe the Usadel equations and review their solution in the case of predicting the transition temperature T C of a thin normal-superconductor bilayer. We also extend this calculation for thicker bilayers to show the dependence on the resistivity of the films. These results, which show a dependence on both the interface resistance and heat capacity of the films, provide important guidance on fabricating bilayers with reproducible transition temperatures.

Microcalorimeter energy-dispersive spectrometry using a low voltage scanning electron microscope

We describe the current performance of the prototype microcalorimeter energy‐dispersive spectrometer (µcal EDS) developed at NIST for X‐ray microanalysis. We show that the low‐energy µcal EDS, designed for operation in the energy range 0.2–2 keV, offers significant advantages for low‐beam‐energy microanalysis. We present several examples in which the prototype µcal EDS has been used to solve problems in low‐voltage microanalysis, including the analysis of tungsten silicide (WSi2), titanium nitride (TiN) and barium titanate (BaTiO3) and the measurement of chemical shifts in Fe and C compounds.

NIST interoperability framework and action plans

The 2007 Energy Independence and Security Act gave NIST the role of coordinating with industry and government stakeholders the development of an interoperability framework for Smart Grid (SG) devices and systems, including standards and protocols. The goal is to achieve seamless interoperability of SG devices and systems across the power system from generator to consumer. With the collaboration of many smart grid stakeholders who provided input through a series of workshops, domain expert working group activities, and other direct interactions, NIST has published the “NIST Framework and Roadmap for Smart Grid Interoperability Standards Release 1.0” document. It includes a conceptual reference model for the SG, standards identified for implementation, a set of standards priority action plans (PAPs), and a cyber security risk management framework and strategy. In 2009, a SG Interoperability Panel (SGIP) that comprises representatives from SG stakeholders across the board was established to further the development of the Interoperability Framework, support the development of new and revised PAPs, and coordination with the Standards Development Organizations (SDOs). This paper reports on progress made in the development and implementation of the Interoperability Framework, the SGIP activities, and on the progress on tasks for standards harmonization and development defined in the PAPs.

Lowering the Limit of Detection in High Spatial Resolution Electron Beam Microanalysis with the Microcalorimeter Energy Dispersive X-ray Spectrometer

Abstract Low-beam-energy X-ray microanalysis with the field-emission-gun scanning electron microscope suffers limitations due to physical factors of X-ray generation. Instrumental limitations are imposed by the poor resolution of the conventional semiconductor energy dispersive X-ray spectrometry. Wavelength dispersive X-ray spectrometry provides sufficient resolution to solve spectroscopic problems, but the poor geometric efficiency and the single channel nature of spectrum measurement restrict its practical use for low-beam-energy microanalysis. The microcalorimeter energy dispersive X-ray spectrometer combines high resolution (

Toward a 2-eV microcalorimeter x-ray spectrometer for Constellation-X

COnstellation-X is a cluster of identical observatories that together constitute a promising concept for a next- generation, high-throughput, high-resolution, astrophysical x-ray spectroscopy mission. The heart of the Constellation-X mission concept is a high-quantum-efficiency imaging spectrometer with 2 eV resolution at 6 keV. Collectively across the cluster, this imaging spectrometer will have twenty times the collecting efficiency of XRS on Astro-E and better than 0.25 arc minute imaging resolution. The spectrometer on each satellite will be able to handle count rates of up to 1000 counts per second per imaging pixel for a point source and 30 counts per second per pixel for an extended source filling the array. Focal plane coverage of at least 2.5 arc minutes X arc minutes, comparable to XRS but with a factor of thirty more pixels, is required. This paper will present the technologies that have the potential to meet al these requirements. It will identify the ones chosen for development for Constellation-X and explain why those were considered closer to realization, and it will summarize the results of the development work thus far.