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Superconducting devices at very low temperatures can be used to measure very small amounts of energy. Using this effect, the Quantum Sensors Group is building single photon detectors for large regions of the electromagnetic spectrum.


The Quantum Microcalorimeter Project in the Quantum Sensors Group develops and applies sensors that detect the energy of single photons or particles. For example, Transition-Edge Sensors (TESs) are able to measure the energy of single x-ray and gamma-ray photons with a precision better than one part per thousand. When assembled into arrays, TESs combine good spectral resolving power and good collecting efficiency in a way that is not possible with other detector technologies. Application areas include materials analysis, astrophysics, and nuclear security.

Major Accomplishments

magazine cover and spectrometer
Left: Cover of the July/August 2014 issue of Synchrotron Radiation News showing an array of NIST's superconducting x-ray sensors installed at the National Synchrotron Light Source. Right: NIST x-ray spectrometer installed at beamline U71 of the National Synchrotron Light Source, Brookhaven National Laboratory. The spectrometer contains 240 x-ray sensors and demonstrates NIST's ability to develop and deliver complete measurement systems.

Development of superconducting x-ray sensor technology and its dissemination to U.S. synchrotron and x-ray free-electron laser (XFEL) light sources: Synchrotrons and XFELs are large facilities that provide x-ray beams of unmatched brightness and quality. As a result, they are heavily used by industrial and academic researchers to understand and develop advanced materials such as next-generation battery components. The Quantum Sensors Group has developed superconducting x-ray sensors that can provide a unique combination of spectral resolution, broad-band response, and collecting efficiency. In order to disseminate these sensors to users at U.S. light sources, the QSG has also developed the cryogenics, readout electronics, and control software needed to construct complete superconducting x-ray spectrometers.

NIST deployed the first of these spectrometers to the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory in 2010, and since then has implemented systems at the Advanced Photon Source (APS) at Argonne National Laboratory and deployed a permanent general-user instrument to beamline 10-1 at Stanford Synchrotron Radiation Lightsource (SSRL) at SLAC National Laboratory. The success and scientific impact of these early instruments has spurred further interest from the x-ray science community. In 2018, the QSG will deploy a second instrument to the SSRL and move the NSLS spectrometer to a new NIST-run beamline at the recently commissioned NSLS-II facility. In 2021, NIST will deliver a 1,000-pixel TES spectrometer to the Linac Coherent Light Source (LCLS) as SLAC. The LCLS is one of only four XFEL’s currently in operation worldwide, and after it completes an upgrade in 2020, will be the brightest x-ray source of any kind. These spectrometers are being used in a wide variety of experiments and measurement techniques, including x-ray emission, absorption, and scattering spectroscopy. An overview of this work was published in J. Ullom et al., Synchrotron Radiation News 27 (2014) 24 and a detailed technical description, including overviews of the breadth of science they enable, is published in R. Doriese et. al., Review of Scientific Instruments 88, 053108 (2017). This work was also described in a recent PML highlight and was awarded a DOC Bronze medal in 2015.

scanning electron microscope
Credit: Robin Cantor
A scanning electron microscope (center-left) with a commercial superconducting x-ray spectrometer (left) developed at STAR Cryoelectronics. The energy resolution of the spectrometer enables elemental and, in some cases, chemical speciation.

Support of commercialization of superconducting x-ray sensors: These high energy resolution x-ray sensors were originally pioneered at NIST, and have considerable potential for materials analysis if they can be developed into spectrometers compatible with the ubiquitous scanning electron microscopes used throughout materials intensive industries. By measuring x-rays produced by the exciting electron beam, these sensors can provide improved elemental and chemical information, as well as information on thinner and smaller structures than is presently possible. The QSG has worked to disseminate this sensor technology so that it can be developed commercially. In particular, the QSG has supported STAR Cryoelectronics' efforts to develop a spectrometer that can be mounted on an electron microscope. STAR Cryoelectronics is a small company located in Santa Fe, New Mexico. STAR now provides a complete commercial instrument based on an array of superconducting x-ray sensors and has already sold several spectrometers to private customers. STAR also provides commercial analysis services using a superconducting x-ray spectrometer located at STAR's Santa Fe facility.

line energy graphs
Histograms of the line energy estimates for eight Lα lines from approximately 100 independent microcalorimeter x-ray sensor measurements.  The error bars show the central estimates and 1σ uncertainties on the peak energy from our work (lower colored bar) and previous NIST reference data (top bar, gray).

Improving the X-Ray Reference Database:  The Quantum Sensors Group initiated a project in 2015 to improve x-ray reference data in order to support emerging needs in industrial and scientific materials analysis. A central goal of this work is an improved tabulation of x-ray line energies and shape profiles. The project is a collaboration between the QSG and three other Divisions at NIST. The QSG will use the high resolving power, broadband response, and high collecting efficiency of its microcalorimeter x-ray sensors to perform absolute energy metrology on a wide range of x-ray lines, including lines that were too weak for exact measurement using previous techniques. Proof-of-principle measurements of x-rays from four lanthanide-series elements were highly successful, establishing the viability of this new technique. The figure on the right shows the absolute line energy estimates for eight Lα lines measured with our microcalorimeter x-ray spectrometer. The histograms reflect the distribution of the line peak energy from approximately 100 independent measurements (one per microcalorimeter sensor). The error bars above the histogram show the central estimates and 1σ uncertainties on the peak energy and compare previous NIST reference data (top bar, gray) and our work (lower colored bar). The large uncertainty for some x-ray lines in the existing tabulation of x-ray line energies and the small uncertainties on the new results clearly demonstrate the potential for improvement in this important database.  These results were published in Fowler, J. W., et al. “A reassessment of absolute energies of the X-ray L lines of lanthanide metals.” Metrologia 54 (4), 494, (2017).  Further measurements of this sort are underway in early 2018 to expand the number of elements studied and to improve the systematic uncertainties in the calibration of absolute energies.

Laboratory-Scale Picosecond X-ray Material Probe: X-rays are among the most common methods to probe materials and chemical reactions. Using picosecond x-ray pulses available at synchrotron and x-ray free electron laser (XFEL) facilities, it is possible to monitor the evolution of chemical changes in materials on the picosecond timescale. This capability is being used to study the pathways of photoreactions in environmentally and technologically relevant molecular systems, such as new solar cell materials. However, beam time at these facilities is very limited, making it possible to explore only a few materials systems with this technique. The QSG has developed a laboratory-scale picosecond x-ray probe system to compliment the more powerful (but much harder to access) XFEL and synchrotron lightsources. This system relies upon an x-ray source that produces picosecond duration pulses from a laser-generated plasma in a liquid jet, and the high resolving power of the NIST-developed superconducting x-ray spectrometer. High impact scientific results from this system include identification of the long-lived spin-crossover state in optically excited iron-tris-bypyridine and elucidation of the process of photo-dissasociation in ferrioxalate. Soon the measurement speed of the system will be increased by a factor of 10 or more when the water jet used to generate x-rays via laser induced plasma is replaced with a liquid metal jet. The first dynamical x-ray results were published in O’Neil, G. C. et. al., The Journal of Physical Chemistry Letters 8 (5), 1099 (2017) and Miaja-Avila, L. et. al., Physical Review X 6 (3), 031047 (2016). The work was also described in a recent NIST News Highlight and received a DOC Gold Medal in 2017.

x-ray probe schematic
Top: schematic of the NIST table-top x-ray probe.  A pulsed laser induces photochemical reactions in the material under study.  The same laser is focused onto a water jet, producing an x-ray generating plasma.  The x-rays are used to interrogate the sample at controlled time delays after photoexcitation.  Bottom: (left) measured time-resolved Kβ emission spectrum of iron-tris-bipyridine probed at a 3 ps time delay.  The spectral shape changes in the excited (pumped) state due to a spin crossover in the system.  (right) resultant time evolution of the high-spin fraction deduced from emission measurements at several time delays.  Our data (see inset) show a fast rise of the high-spin fraction at time-zero followed by an exponential decay (see main figure) of the high-spin-state fraction with a time constant of 566 ± 100 ps.

Credit: Daniel Schmidt
Examples of devices developed by the Quantum Sensors Group to measure the total energy of single radioactive decays. These devices are used by Los Alamos National Laboratory to determine the elemental and isotopic composition of trace radioactive samples. In both devices, a solid silicon platform is suspended by flexible silicon beams. Radioactive samples can be attached to the dark brown squares. The device at left also has an embedded thermometer. A U.S. dime in the background provides scale.

Development of sensors to measure the total energy of single radioactive decay events: The energy released by a single radioactive decay can be used to identify the specific element involved. However, measuring such a small energy is extremely difficult. The superconducting sensors developed at NIST have the energy resolution to perform this measurement, provided they can be engineered into a system compatible with total energy measurements. We have developed new sensors are fabricated on micromachined silicon (rather than silicon nitride) to simultaneously achieve good thermal isolation while preserving mechanical robustness. Robustness is needed to allow the easy attachment of metal foils containing embedded radioactive material, including particulates. The energy of single radioactive decays is sufficient to produce a measurable temperature rise in the sensors. Performed in collaboration with Los Alamos National Laboratory, the goal of this work is to develop new capabilities for nuclear forensics, treaty verification, and environmental monitoring. These sensors have shown their suitability for a wide range of analytical measurements. The attractions of the technique are spectral simplicity, the ability to simultaneously measure multiple isotopes including both alpha- and beta-emitters, and greatly reduced sample preparation. The ability of this technique to accurately measure the mass ratio of the isotopes 240Pu and 239Pu was published in A. Hoover et al, Analytical Chemistry 87 (2015) 3996. This work was also described in a recent PML highlight.

Recent Publications

Sensor Physics:

K. Morgan, et. al., “Dependence of transition width on current and critical current in transition-edge sensors,” Applied Physics Letters, 110 (21), p. 212602, doi:10.1063/1.4984065,2017.

D. Yan, et al., “Eliminating the non-Gaussian spectral response of X-ray absorbers for transition-edge sensors,” Applied Physics Letters, 111 (19), p. 192602, arxiv:1708.08481, doi:10.1063/1.5001198, 2017.

J. Hays-Wehle, et. al., “An Overhanging Absorber for TES X-Ray Focal Planes,” IEEE Transactions on Applied Superconductivity, 27 (4), p. 1–4, doi:10.1109/TASC.2016.2645121, 2017.

J. Hays-Wehle, et. al, “Thermal Conductance Engineering for High-Speed TES Microcalorimeters,” Journal of Low Temperature Physics, 184 (1), p. 492–497, doi:10.1007/s10909-015-1416-5, 2016.

J. Ullom and D. Bennett, “Review of superconducting transition-edge sensors for X-ray and gamma-ray spectroscopy, ” Superconductor Science and Technology, 28 (8), p. 084003, doi: 0.1088/0953-2048/28/8/084003, 2015.

D. Bennett, et. al., “Phase-slip lines as a resistance mechanism in transition-edge sensors,” Applied Physics Letters, 104 (4), p. 042602, 2014.

D. Bennett, et. al., “A Comparison of the Resistively Shunted Junction and Two-Fluid Models for Resistance in Transition-edge Sensors,” Physical Review B, 87 (2), p. 020505, 2013.

D. Swetz, et. al., “Current Distribution and Transition Width in Superconducting Transition-Edge Sensors,” Applied Physics Letters, 101 (24), p. 242603, 2012.

D. Bennett, et. al., “A Two-fluid Model for the Transition Shape in Transition-Edge Sensors,” Journal of Low Temperature Physics, 167 (3-4), p. 102--107, 2012.

Multiplexing Readout and Data Analysis:

J. Mates, et. al, “Simultaneous readout of 128 X-ray and gamma-ray transition-edge microcalorimeters using microwave SQUID multiplexing,” Applied Physics Letters, 111 (6), p. 062601, doi:10.1063/1.4986222, 2017.

J. Fowler, et. al., “When “Optimal Filtering” Isn’t,” IEEE Transactions on Applied Superconductivity, 27 (4), p. 1–4, doi:10.1109/TASC.2016.2637359, arxiv:1611.07856, 2017.

K. Morgan, et. al., “Code-division-multiplexed readout of large arrays of TES microcalorimeters,” Applied Physics Letters, 109 (1), p. 112604, doi:10.1063/1.4962636, 2016.

P. Lowell, et. al., “A thin-film cryotron suitable for use as an ultra-low-temperature switch,” Applied Physics Letters, 109 (14), p. 112604, doi:10.1063/1.4964345, 2016.

J. Fowler, et. al., “The Practice of Pulse Processing,” Journal of Low Temperature Physics, 184 (1), p. 374–381, doi:10.1007/s10909-015-1380-0, 2016.

W. Doriese, et al., “Developments in Time-Division Multiplexing of X-ray Transition-Edge Sensors,” Journal of Low Temperature Physics, 184 (1), p. 389–395, doi:10.1007/s10909-015-1373-z, 2016.

B. Alpert, et. al., “Algorithms for identification of nearly-coincident events in calorimetric sensors,” Journal of Low Temperature Physics, 184 (1), p. 263–273, doi:10.1007/s10909-015-1402-y, 2016.

J. Fowler, et. al., “Microcalorimeter Spectroscopy at High Pulse Rates: a Multi-Pulse Fitting Technique,” The Astrophysical Journal Supplement Series, 219 (35) 2015.

G. Stiehl, et. al., “Code-Division Multiplexing for X-ray Microcalorimeters,” Applied Physics Letters, 100 (7), p. 072601, 2012

J. Fowler, et. al., “Optimization and Analysis of Code-Division Multiplexed TES Microcalorimeters,” Journal of Low Temperature Physics, 167 (5—6), p. 713--720, 2012.

W. Doriese, et. al., “Optimization of the TES-bias Circuit for a Multiplexed Microcalorimeter Array,” Journal of Low Temperature Physics, 167 (5-6) p. 596--601, 2012.

Science Results and Applications:

C. Titus, et. al., “L-edge spectroscopy of dilute, radiation-sensitive systems using a transition-edge-sensor array,” The Journal of chemical physics, 147 (21) p. 214201, doi: 10.1063/1.5000755, 2017.

J. Fowler,et al., “A reassessment of absolute energies of the X-ray L lines of lanthanide metals,” Metrologia, 54 (4), p. 494, arxiv:1702.00507, 2017.

W. Doriese, et. al., “A practical superconducting-microcalorimeter X-ray spectrometer for beamline and laboratory science,” Review of Scientific Instruments, 88 (5), p. 053108, doi:10.1063/1.4983316, 2017.

G. ONeil, et al., “Ultrafast time-resolved X-ray absorption spectroscopy of ferrioxalate photolysis with a laser plasma X-ray source and microcalorimeter array,” The Journal of Physical Chemistry Letters, 8 (5), p. 1099–1104, 2017.

L. Miaja-Avila, et al., “Ultrafast Time-Resolved Hard X-Ray Emission Spectroscopy on a Tabletop,” Physical Review X, 6 (3), p. 031047,doi:10.1103/PhysRevX.6.031047, 2016.

S. Okada, et al., “First application of superconducting transition-edge sensor microcalorimeters to hadronic atom X-ray spectroscopy,” Progress of Theoretical and Experimental Physics, 2016 (9),p. 091D01, doi:10.1093/ptep/ptw130, 2016.

M. Palosaari, et. al, “Wide-Energy-Range High-Resolution Particle Induced X-ray Emission Spectroscopy with Superconducting Microcalorimeter Arrays,” Physical Review Applied, 6 (2), p. 024002,doi:10.1103/PhysRevApplied.6.024002, 2016.

R. Cantor, et. al., “Oxidation State Determination from Chemical Shift Measurements using a Cryogen-Free Microcalorimeter X-Ray Spectrometer on an SEM,” Microscopy and Microanalysis, 22 (S3), p. 434–435, doi:10.1017/S1431927616003020, 2016.

H. Tatsuno, et. al., “Absolute energy calibration of X-ray TESs with 0.04 eV uncertainty at 6.4 keV in a Hadron-beam environment,” Journal of Low Temperature Physics, 184 (3), p. 930–937, doi:10.1007/s10909-016-1491-2, 2016.

J. Uhlig, et al., “High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential,Journal of Synchrotron Radiation, 22 (3), p. 766–775, 2015.

Y. Joe, et. al., “Observation of Iron Spin-States using Tabletop X-ray Emission Spectroscopy and Microcalorimeter Sensors,” Journal of Physics B, 49 (2), p. 024003, doi:10.1088/0953-4075/49/2/024003, 2015.

Hoover, et. al., “Measurement of the 240Pu/239Pu Mass Ratio Using a Transition-Edge-Sensor Microcalorimeter for Total Decay Energy Spectroscopy,” Analytical chemistry, 87 (7), p. 3996–4000, 2015.

B. Alpert, et. al., “HOLMES: The Electron Capture Decay of163Ho to Measure the Electron Neutrino Mass with sub-eV Sensitivity,” The European Physical Journal C, 75 (3), p. 1–11, 2015.

S. Okada, et. al., “High-resolution kaonic-atom x-ray spectroscopy with transition-edge sensor microcalorimeters,” Journal of Low Temperature Physics, 176 (5–6),p. 1015–1021, 2014.

J. Uhlig, et. al., “Table-top ultrafast x-ray microcalorimeter spectrometry for molecular structure,” Physical Review Letters, 110 (13), p. 138302, 2013.

D. Bennett, et al., “A High Resolution Gamma-ray Spectrometer Based on Superconducting Microcalorimeters,” Review of Scientific Instruments, 83 (9), p. 093113, 2012.

Highlights and Outreach:

Department of Commerce Gold Medal, 2017
"For advancing materials development by creating tabletop X-ray tools that rival or exceed those available only at massive national user facilities"

American Institute of Physics Highlight of the Year, 2017
"New SQUID-Based Detector Opens Up New Fields of Study with New Level of Sensitivity"

American Institute of Physics Scilight,  2017
"Electroplated bismuth absorbers yield efficient, high-energy-resolution X-ray detection"

Symmetry Magazine Dimensions of Particle Physics,  2017
"Instrument finds new earthly purpose"

NIST News Highlight 2016:
“Seeing Light’s Effects on Atoms — Within Picoseconds"

Department of Commerce Bronze Medal, 2015
"For providing new capabilities to preeminent international research facilities through the dissemination of revolutionary X-ray spectrometer systems"

RIKEN Nishina Center Highlight of the Year,  2015
"High resolution hadronic-atom x-ray spectroscopy with superconducting TES microcalorimeters"

NIST Physical Measurement Laboratory's News Highlights, 2015
“Getting a Critical Edge on Plutonium Identification''

NIST Physical Measurement Laboratory's News Highlights,  2014
"New High Resolution X-ray Spectrometers for Beamlines"

Created March 13, 2018, Updated April 23, 2019