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Sensor Science Division

The vision of the Sensor Science Division (SSD) is to be the primary driver for innovation in the International System of Units (SI)-traceable measurement of dimensional, thermodynamic, and optical radiation quantities, enabling the next generation of equitable standards to promote U.S. economic growth and security. The mission of the division is to foster the next generation of SI-traceable, dimensional, thermodynamic, and optical radiation measurements and their applications by providing calibrations, standards, and innovations that improve U.S. industrial competitiveness and quality of life.

The division is organized into the following seven groups: the Dimensional Metrology Group, Fluid Metrology Group, Optical Radiation Group, Remote Sensing Group, Surface and Interface Metrology Group, Thermodynamic Metrology Group, and Ultraviolet Radiation Group. The groups work collaboratively on nine major topics—measurement services and documentary standards, large-scale dimensional metrology, metrology for extreme ultraviolet (EUV) lithography, forensics topography and surface metrology, providing SI traceable measurements to support the energy sector, low-background infrared radiometry, climate change and greenhouse gas, thermodynamic metrology, and optical metrology for solid-state lighting.

With its institutional responsibility for the realization and dissemination of three of the seven base SI units—the meter, the kelvin, and the candela—the SSD is tasked with SI-traceable measurements of length, temperature, infrared-to-EUV radiation, pressure and vacuum, surface and interface optical and dimensional properties, gas and liquid flow, liquid volume, and humidity. Across SSD’s groups and programs, the division is responsible for developing, maintaining, and disseminating national measurement standards for these physical quantities; performing measurement comparisons internationally to support U.S. competitiveness in the global marketplace; performing research for new measurement technologies, methods, and national needs; and providing measurement services, including the calibration of practical standards and measurement instruments. The list of stakeholders reliant on and requesting NIST impartiality and quality for SI-traceable measurements continues to grow.

TECHNICAL QUALITY OF THE WORK

While it is not the role of NIST to specify technical requirements, NIST plays an important role in measurement services and documentary standards, advising on measurement techniques and collaborating with industry in the development of technical standards. The SSD is engaged in over 25 Standard Development Organizations (SDOs) worldwide. Approximately one-third of the staff are actively involved in producing documentary standards, and they hold about 58 leadership positions in these organizations. Billions of dollars in dimensional metrology equipment are bought and sold using performance specifications from standards developed under SSD leadership and with SSD-developed models serving as the technical foundation. This work has resulted in 16 major documentary standards and draft documentary standards published since 2017. SSD contributions to dimensional metrology have been recognized by the ASTM James A. Thomas President’s Leadership Award and the NIST Edward Bennet Rosa Award. NIST staff have also been recognized for their outstanding contributions by awards from the International Commission on Illumination, Acoustical Society of America, American Society for

Mechanical Engineering (ASME), NASA, the American Vacuum Society (AVS), ASTM International, and NIST.

The SSD is currently involved in 19 key comparisons and 16 regional comparisons, which help to establish equivalence of measurement standards across national metrology institutes. The published results of these key comparisons confirm that NIST staff demonstrably are leaders in many measurement disciplines, achieving some of the lowest measurement uncertainties in the world. In terms of impact on advanced manufacturing, it is important to note that nearly all large-scale metrology tools are specified and tested according to standards developed under SSD staff leadership.

Stakeholders purchased $2.2 million of products of SSD measurement services (calibration services, standard reference materials, laboratory accreditation, and training courses) in fiscal year 2020. The measurement services of the SSD account for more than half of the total NIST calibrations performed, corresponding to 4,000 artifacts per year. An impressive example of leverage is that four NIST-calibrated reference flow meters are used by one manufacturer to calibrate 50,000 mass flow controllers.

SSD staff and leadership expressed a concern that they had lost contact with key customers with the implementation of the NIST Storefront, which provides an Internet interface through which NIST measurement services are procured. Both end users and staff expressed displeasure in using the current Amazon-like interface to procure and deliver services. This may have had several detrimental effects. While returning customers provide formal and informal feedback, some traditional customers of NIST (major industry segments, Department of Defense [DoD]) have not been able to obtain some needed services. Specifically, the long times for some calibrations to be completed, the discontinuation of some measurement services, such as the cryogenic liquid flow metrology and the high costs charged to customers, are jeopardizing NIST’s position of providing SI traceability for U.S. commerce and national security.

Because NIST typically works with critical, but few-in-number, customers at the top of the traceability pyramid, it may be beneficial to contact these customer segments to understand better their measurement needs, which have significant impact on the industrial competitiveness and on the U.S. security and defense infrastructure. Some NIST calibration services perform well; others could benefit from improvement. It would be beneficial for SSD to consider ways to give customers better estimates of delivery times for calibration services and provide direct, timely notification when services are not available. The SSD might, in collaboration with other NIST divisions, consider having a customer rating system on individual services to identify top performers in terms of service metrics and other areas where customer service might be improved. This would also likely be useful in quantifying the impact of individual measurements performed within SSD, as well as in clarifying the division’s priorities. For example, the impact of flow calibration for Brooks was clear. It would be appropriate for the SSD to maintain a record of which measurement services have been phased out and why, as well as those added. SSD staff reported that some measurement services were not available during renovation of laboratory space, and other measurement services have been severely impacted by maintenance issues in aging buildings. Renovation of some of the facilities is planned but will take many years to complete.

The SSD has a worthwhile involvement in the NIST-on-a-chip (NOAC) initiative, which can realize the SI directly or disseminate measurements based on properties of nature, whereby the traceability chain can be short-circuited to allow standard sensors to exist extramurally. This initiative could develop a process that would likely result in significant economic savings for industrial users without compromising measurement standards. This effort is extremely forward thinking, and NIST is to be commended for putting thought and resources behind an initiative that could potentially obviate some of its services and make NIST traceability and error reduction easier.

A key feature of NOAC is the design, fabrication, and dissemination of embedded, SI-traceable sensors that can be incorporated directly into instruments, eliminating NIST as a middleman while minimizing sources of uncertainty. Candidate projects for NOAC were identified organically by SSD scientists through a standard NIST proposal review system, which takes advantage of significant staff enthusiasm and engagement with the NOAC effort. However, there might be missed opportunities for

identifying other, more important NOAC targets, or places for improved efficiency in identifying targets that offer more direct or convenient NOAC integration. The enthusiasm of SSD scientists could be channeled into a systematic review of potential targets for NOAC integration to create an overall strategy. Such a review could identify new and deserving targets and also identify targets that could reach technological maturity faster in order to demonstrate NOAC capabilities and accelerate industry acceptance. Thermodynamic metrology capabilities would benefit from such a review, as well as other groups that are pursuing NOAC integration. An additional concern with respect to NOAC development is the need for a reasonable estimate of the cost of delivering an NOAC to a customer and a clear idea of what types and numbers of customers will purchase and use such devices. With its stated goal of creating embedded, SI-traceable calibration chips that can be incorporated directly into instruments, it will be important for NIST to understand the value proposition for specific customers that NIST expects will purchase and embed such chips into their systems. At the end of the review, the panel learned that there had been a strategic planning exercise for NOAC but were not given any details of whether any customers participated. NIST has developed a roadmap for NOAC, but it was not shared with the panel due to confidentiality concerns. As a result, the examples of NOAC within PML seemed unconnected.

Staff scientists and engineers in SSD have been and continue to be pioneers in large-scale dimensional metrology. SSD operates and maintains research and calibration facilities for such measurements that are among the best in the world and have been used as models for other industrial and national metrology institutes (NMIs). SSD staff invented laser scanning methods that enable precision, traceable measurements with on-the-order-of micrometers of uncertainty for length measurements for scales involving tens of meters or more. The identification of the previously unknown source of error in commercial laser trackers led to creation and dissemination of the NIST geometric model through national (ASME B89-4-19) and international (ISO 10360-10) standards. Other outputs of NIST’s research have been embedded in ASME standards for tactile coordinate measuring machines (CMMs), articulated arm CMMs, laser trackers and scanners, and X-ray-computed tomography. NIST has had good collaboration with industry in this area, leading to several CRADAs to build artifacts to test laser scanning systems, and the testing procedures associated with them have also been integrated into ASME standards.

The SSD has been a key driver in metrology for the economically important area of EUV lithography, an essential tool for semiconductor manufacturing and continuation of Moore’s Law, which predicts that the area density of transistors on a chip will double every 2 years. Increasing transistor densities that are represented by the transition from the 10 nm node to the 7 nm node, and now to the 5 nm and 3 nm nodes, require shorter wavelengths of EUV radiation in the lithography tools used to make them. The SSD has been involved in key collaborations in the metrology for EUV lithography, including optics lifetime, photoresist characterization, and source radiometry due to the capabilities of the Synchrotron Ultraviolet Radiation Facility (SURF III). SURF III is an important source of ultraviolet (UV) radiation, with its spectral peak output near the wavelength of EUV lithography (13.5 nm). The SSD used this capability for industry collaborations in the areas of testing EUV optics lifetimes and identifying optics degradation methods; photoresist characterization (e.g., all advanced semiconductor materials lithography) witness samples worldwide are traceable to NIST); and source radiometry (photodiode calibration), which has aided the industry transition. For example, the Apple APU (accelerated processing unit) for the iPhone is made with EUV lithography. The SSD has active CRADAs and precompetitive and proprietary work going on with 11 industry players. Industry testimonials attest to the importance of NIST and the SURF III to this critical industry transition. Specific SSD research and development accomplishments include a model of optic degradation and identification of degradation mechanisms for satellites. Upgrades of the SURF III facility have been beneficial for this strategic work. NIST is prepared for the transition to 6.7 nm with SURF III, with light output at this wavelength though at a lower intensity than at 13.5 nm. The SSD is well connected to this industry and has the opportunity to continue to contribute as the industry transitions to 5 nm and 3 nm, while also providing valuable service to the scientific customer base.

In the area of forensics topography and surface metrology, the SSD conducts calibrations of transfer standards for surface roughness, step height, lateral spacing, and microform geometry for manufacturing, forensics, and science. As an example, it provides the world’s lowest measurement uncertainty for the microform geometry of standard hardness Rockwell-C diamond indenters used in certification of NIST hardness standards. The Forensic Toolmark Analysis Project serves as a case study in this area. Firearm and toolmark identification currently relies on subjective evaluation of toolmark similarity. SSD facilitated the transition to repeatable 3D topography measurements, developed objective similarity metrics, and developed initial statistical models for error rate and weight of evidence estimations. It has also created an open-access research database of two-dimensional (2D) and 3D toolmark images from a diverse population of firearms and a reference population database of firearm toolmarks. This fosters the development of further measurement methods, algorithms, and metrics that are likely to offer opportunities for machine-learning methods. The research team is well connected to standards organizations and federal, state, and local laboratories, including the Federal Bureau of Investigation and the National Institute of Justice, which have supported and/or collaborated on these projects.

Challenges in this area include being able to address industry and manufacturing needs while also addressing the toolmark project. Opportunities not met with current resources include optical metrology for rougher surfaces, including the important application of optical surface finish metrology for additive manufacturing. One of the most significant challenges is the rapid pace of change in firearms that require research to address. The ability to address them is limited by staffing resources. The development of the national database is time and labor intensive. The team is trying to develop automated systems for the Federal Bureau of Investigation, but that also will take additional resources.

In the area of providing SI traceable measurements to support the energy sector, the SSD plays a vital role in calibrating custody transfer flow meters for natural gas, affecting the sale and use of $300 × 10⁹ of natural gas per year. The successful collaboration with CRADA partner CEESI (Colorado Engineering Experiment Station, Inc.) has allowed for calibrations with SI traceability to continue. A multi-million-dollar project to reduce uncertainty from 0.35 to 0.2 percent is near completion. The SSD works with the American Petroleum Institute (API) to provide calibration of the approximately $5 × 10¹² per year sale of petroleum products. API documentary standards require recalibration of test measures every 5 years, with SSD involvement in the recalibration due to its impartiality, measurement consistency and quality protocols, and the SSD’s continuing research to improve liquid volume measurements. Of particular note are the use and continuing improvement of automation methods for volume transfer.

One concern in this area is the loss of the cryogenic liquid flow meter calibration capability for liquid natural gas. The facility was shut down and transferred to CEESI, the NIST CRADA partner that also performs ambient flow meter calibrations and who agreed to provide calibrations. Due to changing circumstances at CEESI, CEESI is no longer performing those calibrations and has shut down the facility. VSL, the Netherlands NMI, is the only NMI that does such calibrations. Although SSD staff will be working with VSL to establish comparability with NIST measurements when the VSL facility reopens later this year, the lack of a U.S. calibration facility for such an important U.S. industry is of concern, especially given the industry’s requests to NIST to reinstate the capability.

The Low-Background Infrared Radiometry program is the primary source of calibrations for a key national security customer, the Missile Defense Agency (MDA). The program includes two main elements—calibration of cryogenic blackbody sources and transfer radiometers for calibration of user test chambers. The SSD’s support of DoD programs has been ongoing for over three decades and is gradually evolving because of the requirements for higher sensitivity calibrations. While the direct funding to NIST for this program has remained constant for some time, the MDA provides significant staffing for the effort at NIST. The SSD effectively engages in research to support these increasing demands. For example, there is emphasis on innovation of cryogenic radiometric devices and methods to improve sensitivity and speed. The program interfaces with groups at NIST Boulder to employ novel nanotube radiometers, thus giving it a pathway to be integrated into the NOAC initiative and eventually allow miniaturization and easier traceability.

The main challenge to the program is the lack of diversity in the customer base, with MDA being the principal customer over the entire period of existence of the program. This poses a considerable risk if the customer needs change; hence, it would seem advisable to pursue a more vigorous approach to engage with other potential customers. The recent collaborations with NASA, the International Thermonuclear Experimental Reactor, and the Air Force are laudable and may present a springboard for program diversification.

The Climate Change/Greenhouse Gas program builds upon the mature and successful spectral irradiance and radiance responsivity calibration with uniform sources (SIRCUS) capability, which enabled pre-flight calibration methods for Earth-observing satellites, was transitioned to NASA, and is now used by multiple industrial customers. The satellite calibration service is critical to supporting the global effort to understand and mitigate the effects of climate change through improved measurements of parameters used in climate modeling. An impressive recent accomplishment is the development of the telescope for lunar spectral irradiance calibration, which is suitable for deployment on a high-altitude aircraft and was successfully deployed in a demonstration flight campaign. This facility realized a considerable reduction of lunar spectral irradiance measurement uncertainty, helping to improve climate measurements from satellites. Complementary to space-based observations, the program also developed methods to perform greenhouse gas measurements at industrial facilities. Its success in reducing the uncertainty and increasing the speed of smokestack flow measurements is admirable and highlights the merits of immediate stakeholder engagement, which, in this case, led to a successful field demonstration. Of particular note was the use of the NIST smokestack simulator in enabling design of the NIST hemispherical 3D airspeed sensor, which reduced errors from 17 to 1 percent.

Engaging in new programs such as ocean-color measurements, forest productivity, and solar-induced fluorescence highlights the potential for making key contributions in other areas of relevance to climate. The growing awareness and investment of resources in addressing the climate change challenge globally underscores the need to develop a strategic plan of engagement to prioritize the use of program’s resources and enable its growth through staffing and facilities. It appears that such a roadmap currently does not exist, and it could be developed in collaboration with other PML, NIST, and other governmental and industrial programs.

Work on pressure measurement is representative of SSD’s strength in the area of thermodynamic metrology. The researchers identified an outstanding need in the area of deepest vacuum, where the existing pressure gauge technology, in the form of ionization gauges, could not quantify this level of vacuum due to the requisite contamination that accompanies this previous state-of-the-art approach. The group responded to this need by developing a new methodology, the cold-atom vacuum standard (CAVS). More nascent efforts that leverage existing SSD strengths in emissive defects, optical cavities, and optomechanics suggest a rich pipeline for further advances in thermodynamics metrology.

SSD researchers in the area of optical metrology for solid-state lighting provided several examples supporting their leadership in this area over the past 15 years. For example, NIST protocols for stray-light correction and temperature-compensation of light efficiency have become industry standards and, in some cases, have helped lay the groundwork for societal acceptance of new lighting solutions. New work on vision science, including color quality of light-emitting diodes, flicker perception, and glare, will continue NIST leadership. Newer facilities and products, including a uniquely massive integrating sphere, automated photometry bench, new transfer standards, and a setup to show the effects of different illumination on human perception, are likely to allow this group to expand their revenue from services, which is already in excess of $300,000 per year. Some of these accomplishments were enabled by industry partnerships via CRADAs, small business innovative research grants, and patents. One demonstration of NIST leadership in this area is best-in-the-world low uncertainty in maintaining the candela standard, as demonstrated in 2018. SSD human resources and technical capabilities in this area continues to be among the best in the world.

SSD staff made commendable contributions during the COVID-19 pandemic. From March 2020, when staff were required to work remotely, division staff ensured that essential calibrations were performed for their customers in support of national security, national well-being, and commerce.

Directly related to the pandemic, SSD staff conducted special projects on germicidal UV (GUV), including measurements of the UV action spectrum for the deactivation of SARS-CoV-2 in collaboration with the Department of Homeland Security; development of documentary standards for UV sources, and a UV–SIM (Inter-American Metrology System) workshop and UV radiometer distribution; N95 mask disinfection using GUV in response to shortages in personnel protective equipment; education on proper calibration procedures and use of ambient radiation thermometers through a workshop with 50 metrologists from 15 countries in the Americas; and standards for vaccine cold storage and transport vaccine with the Centers for Disease Control and Prevention (CDC). There has been a 12-year collaboration between SSD’s Thermodynamic Metrology Group and the CDC’s Vaccine Supply and Assurance Branch on standards and best practices for vaccine cold storage and transport. This effort illustrates the broad reach of NIST in ensuring national well-being, beyond national defense and economic competitiveness. SSD staff have assisted with the COVID-19 vaccine rollout, addressing critical questions related to the transport and monitoring of frozen vaccine. Division staff are likely to have continuing roles during this pandemic and in potential future crises. This may have an effect on other roles and responsibilities of SSD staff. It is hoped that additional resources can be made available to ensure that other high-priority programs are not affected.

TECHNICAL EXPERTISE OF THE STAFF

The technical staff for the SSD are internationally respected experts in metrology. The staff holds fellowships in the International Society for Optics and Photonics (SPIE), American Physical Society, AVS, ASTM, ASME, Acoustical Society of America, and the Illuminating Engineering Society. Division staff facilitate global best-metrology practices at an international level through the Bureau International des Poids et Mesures (BIPM) consultative technical groups in thermometry, photometry, and radiometry. The researchers’ creativity and elite status in measurement science are illustrated by several recent awards, a commendable rate of production of papers and patents, and leadership in high-visibility initiatives to safeguard national artifacts. These efforts are excellent examples of creativity resulting in unique and best-in-world capabilities, and these efforts are likely to result in continued SSD leadership in these areas.

Overall, NIST and SSD support of standards development is impressive. For example, a NIST staff member was a co-convener for the revision of International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) 17025, the most important competency-based standard for calibration and test laboratories. An SSD staff member is a participant in the revision of ISO/IEC 17043, general requirements for proficiency testing, which is used as a reference for both key comparisons and measurement assurance programs that NIST coordinates. The division leads global documentary standards activities for general measurement competency and specific industrial sectors, in support of the NIST, PML, and SSD missions.

ADEQUACY OF RESOURCES

The aging infrastructure has negatively affected performance of mission-critical activities in the form of facilities downtime, burdening technical personnel (because they have to spend time reacting to and compensating for deficient environmental conditions and not in performing measurements), and systematic degradation of performance metrics. Although examples of issues with NIST infrastructure were given throughout the review, some of the most conspicuous were in the Thermodynamic Metrology Group. Poorly controlled laboratory humidity keeps experiments using the CAVS tool from being routinely conducted, often for months at a time. SSD staff also reported having to do makeshift or temporary repairs and solutions to compensate for a lack of long-term environmental upkeep; this constitutes weak temporary solutions that ultimately result in more sudden or catastrophic failures.

Maintenance is funded locally, rather than centrally, and service is generally slow and inadequate. The apparent dearth of proper, environmentally stabilized laboratory conditions and proper building maintenance are significant impediments to performance of mission-critical activities. Building renovations are planned but will take many years at their current pace—a pace that is limited by the NIST budget. Building maintenance is slow and inadequate, with the staff performing makeshift repairs that often delayed, but did not prevent, catastrophic failure.

Hiring of additional technician-level staff would significantly streamline calibrations and other experiments and would elevate the ability to meet industry’s measurement needs while maximizing the efficient time for staff at the ZP-level pay band. Division staff mentioned in several groups and programs that productivity would increase if there were additional technicians in the division. This may be a matter of having enough available funding or in how headcount is approved—that is, if one new hire per year can be added, it may be more likely that it will be a Ph.D., even though two technicians are needed. An alternative or complementary strategy could be to provide added support for the continuing development of automation capabilities to streamline routine calibrations, where possible.

Maintaining the high level of expertise over time is a critical concern. SSD staff reported continuing challenges in hiring postdoctoral researchers, which are often the entry-level position for Ph.D. hires at NIST and in succession planning. With respect to postdoctoral researchers, particularly NRC postdoctoral researchers, the issue is the fierce competition for them between base metrology programs and other areas of science. The SSD recently was able to bring on two postdoctoral researchers, but that seems a low number given the size of the division. The difficulty in succession planning is a continuing, serious issue that cannot be addressed without guidance and support from upper management at NIST.

EFFECTIVENESS OF DISSEMINATION OF OUTPUTS

SSD staff published 240 archival journal papers, technical reports, conference proceedings, and book chapters in the past 3 years. Many of those publications appear in prominent scientific journals with high impact. Division staff members have presented over 50 invited talks nationally and internationally in this period. These metrics attest to the high quality of research and development activity and the division culture to widely disseminate the output to the benefit of the public. The division is active in participating in or leading interlaboratory measurement comparisons, which generate cooperative agreements with industry, government, and universities, as well as interagency agreements. SSD staff participate in over 25 standards developing organizations and consultative committees that produce documentary standards, leading approximately 58 of these committees, with 8 documentary standards and draft documentary standards in dimensional metrology published since 2017. Fourteen patents have been issued for innovations developed by the division in the recent period.

Continued engagements in standards organizations, professional society leadership, journal editorship, and conference/workshop organization can have a large multiplying effect on dissemination and personal career development. Additionally, effective outreach to show the importance of measurement science at the K-12 level is an opportunity that could reap long-term benefits to NIST staffing and society as a whole. Maintaining and incentivizing these activities is a prudent practice.

GENERAL CONCLUSIONS AND RECOMMENDATIONS

The SSD has excellent programs, with an equally excellent staff, aligned with the SSD and NIST mission. Its impact on industrial competitiveness, public well-being, and national security is significant. The full scope of its activities is broad and diverse. SSD staff hold key leadership roles in national and international standards organizations vital to fulfilling the NIST mission. Their efforts to put themselves out of some current business and open up new opportunities through the NOAC and through new implementations of automation for calibration are commendable. The division has recently started a

strategic planning exercise with the staff, with the initial outcomes being more open communication and trust, which are necessary first steps in setting priorities for a division with such a broad portfolio of activities. The SSD staff would benefit from clear metrics for the impacts of the division’s portfolio of activities and understanding of division priorities and resource allocation.

Customers of SSD have expressed dissatisfaction with the timeliness with which measurement services are delivered and with the lack of sufficient feedback during the process of performing the services.

Aging infrastructure is a serious issue. It is affecting performance and will ultimately affect NIST’s reputation. This is a NIST-wide issue that is noted here to highlight the urgency with which it needs to be addressed.

Having adequate staffing levels continues to be an issue for the SSD with respect to hiring postdoctoral researchers and technicians and being able to do meaningful succession planning. These require more financial resources and/or a realignment of programmatic priorities.