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Annual Report 2022

Division 7
Cover photo: Water triple point cell

The year 2022 was again very successful for Division 7. Third-party funding, publications, and academic degrees on the one hand, and calibrations, reviews, and committee work on the other, remained at a high level with slightly lower staffing. Accordingly, the feedback on the work and task planning by the presidium was consistently positive.

Dr. Jörn Beyer, Head of Department 7.6, received this year's IEC 1906 Award from the International Electrotechnical Commission. Dr. Andreas Steiger, Working Group Leader 7.34, received the Andy Chi Best Paper Award at the IEEE International Instrumentation and Measurement Technology Conference (I2MTC) 2022. Dr. Christian Monte, Working Group Leader 7.32, was appointed Head of Department 7.3 Detector Radiometry and Radiation Thermometry on October 1, succeeding Dr. Jörg Hollandt, who had held this position with great success for many years.

The retirement of colleagues, some of whom are very experienced, has so far been well compensated for by new hires and transfers of functions, despite the difficult labor market for skilled workers. Division 7 has become more diverse as a result. Due to the age distribution, however, personnel development at all levels continues to represent a major risk and remains a central issue for the division.

Since 2019, PTB has been orienting its research and development work towards the metrological future topics of quantum technology, environment and climate, energy, digitalization, and medicine. This also applies to Division 7 with its core competences in the fields of thermometry, thermal energy, cryosensors, vacuum metrology, optical radiometry and metrology with synchrotron radiation.

Figure 1: Cornelia Aßmann (Working Group 7.62) in the Walther Meissner Building at the state-of-the-art scanning electron microscope as a central instrument for the structural and chemical diagnostics of cryosensor thin film circuits [©KLAPSCH].

The complex facilities in Division 7 for quantum technology (SQUID development, cryosensor technology, cryogenic and primary thermometry, photonic pressure measurement) are currently being transferred to the new Walther Meissner Building and successively put into operation there (Fig. 1).

On April 22, 2022, the Walther Meissner Building, the Berlin branch of PTB's Quantum Technology Center, was handed over to PTB by the Federal Office for Building and Regional Planning (BBR) and ceremonially inaugurated (Fig. 2). In the next few years, a modern application laboratory for quantum technology will be established here in close cooperation with the technology transfer partners Magnicon GmbH and Entropy GmbH, combined with the expansion of the existing networks, in particular with the Berlin universities, the European Metrology Partnership and the metrology institutes in the USA (NIST) and Japan (AIST).

Figure 2: Inauguration of the Walther Meissner Building on April 22, 2022, at the Berlin Institute of PTB. 1st row (from left to right): Doreen Wernicke (Entropy GmbH, Managing Director), Prof. Dr. Dr. h.c. Joachim Ullrich (then President of PTB), Petra Wesseler (President of BBR), Canan Rohde-Can (Rohdecan Architekten GmbH), Prof. Dr. Cornelia Denz (now President of PTB), Prof. Dr. Dr. h.c. mult. Klaus von Klitzing (honorary member of PTB’s Advisory Board), Dr.-Ing. Prof. h.c. Frank Härtig (Vice President of PTB), Prof. Dr. Mathias Richter (Head of the Temperature and Synchrotron Radiation Division of PTB) 2nd row (from left to right): Henry J. Barthelmess (Magnicon GmbH, Managing Director), Dr. Frank Melchert (Head of Technical-Scientific Infrastructure of PTB in Berlin), Eckart Rohde (Rohdecan Architekten GmbH), Prof. Dr. Tobias Schäffter (Head of the Berlin Institute of PTB), MinDirig Dr. Ole Janssen (Federal Ministry for Economic Affairs and Climate Action), Heiko Körner (BBR), Dr. Jörn Beyer (Head of the Cryosensors Department of PTB) [©PTB].

Parallel to the move to the Walther Meissner Building, the work in the affected areas continues. For example, the sensor fabrication for a new multi-channel system for SQUID magnetometry in ultra-low field environment was completed in Working Group 7.62 in cooperation with Working Group 8.24. In cooperation with partners at the Helmholtz-Zentrum Berlin (HZB), the Norwegian University of Science and Technology, and the Max Planck Institute for the Structure and Dynamics of Matter, a novel SQUID magnetometer setup for investigations on weakly magnetic materials could also be developed in Department 7.6.

Figure 3: Top view of the DART board (green) with connectors (light gray) and housing (dark gray). The measuring amplifier is provided with an additional shielding housing (black), the cover of which has been removed for illustration.

In a cooperation between Working Group 7.44 and the Royal Holloway University of London, a comparison of two different SQUID-based noise thermometers (pMFFT, CSNT) in the temperature range from 0.2 mK to 220 mK was carried out. The new Dual-mode Auto-calibrating Resistance Thermometer (DART, Fig. 3) developed in Department 7.6, which combines temperature measurement with industrial platinum resistance thermometers and primary noise thermometry, has been patented for commercialization.

The EU project QuantumPascal, coordinated by PTB, for new quantum-based pressure standards based on optical, microwave-based, and dielectric methods was successfully completed in November 2022. A method for the in-situ determination of the frequency penetration depth of coated mirrors in Fabry-Perot (FP)-based refractometers was also presented.

Figure 4: Wide-angle X-ray scattering from a perovskite solar cell with and without irradiation by a blue LED [N. Phung et al, Joule 6, 2152 (2022)].
Figure 5: Principle of passive radiant cooling of buildings by special white roof colors.

The topic of energy is dealt with in Division 7 under many aspects. Within the framework of the MetHyInfra project (20IND11), the first measurements were carried out in Working Group 7.43 in close cooperation with Working Group 1.45 and 1.42 and with the support of Working Group 7.52 on a flow measuring section for cryogenic media in order to investigate the behavior of flow measuring instruments under cryogenic operating conditions, in particular for hydrogen technology. In novel high-efficiency perovskite solar cells, lattice changes by irradiation were investigated in the PTB laboratory at the synchrotron radiation source BESSY II by means of wide-angle X-ray scattering in Working Group 7.21 together with researchers from HZB (Fig. 4).

Two new research projects of Working Group 7.32 focus on passive radiative cooling (PRC) of buildings. PRC materials can effectively reflect solar radiation and simultaneously dissipate heat. Even with direct irradiation, temperatures below the ambient temperature can be achieved and energy savings achieved in building air conditioning. PaRaMetriC is an EPM project for the performance evaluation of passive radiant cooling and the optimization of PRC materials. In contrast, the objective of the Cool White cooperation project of the BMZ and PTB is to investigate the cooling effect of special white paints on roofs (Fig. 5).

However, radiation thermometry in Working Group 7.32 also contributes to a more precise modeling of the consequences of climate change. Thus, a Memorandum of Understanding was agreed between the National Institute of Standards (NIST), the Laboratory for Atmospheric and Space Physics (LASP) in the USA and PTB for the development of radiometers and extraterrestrial observation of the Earth's infrared radiation budget.

The eleventh International Aerosol Conference IAC 2022 in Athens was also held under the heading Climate and Environment, where current results of the EMPIR project AEROMET II, coordinated by Working Group 7.24 X-ray spectrometry, were presented in a dedicated session on advanced aerosol metrology for atmospheric science and air quality.

Figure 6: Far-infrared spectroscopy with synchrotron radiation enables the study of the mechanistic behavior of antimicrobial peptides (AMP) in reconstituted biomembranes and the monitoring of membrane-mediated antimicrobial interactions [A. Hornemann et al., ChemPhysChem 23, e202100815 (2022)].

Department 7 is not represented in PTB’s Innovation Cluster (IC) Health but contributes to its content. For the characterization of antimicrobial peptides, far-infrared spectroscopy was successfully applied at the Metrology Light Source (MLS) of PTB in cooperation of Working Group 7.11 and 7.24 with the synchrotron radiation facility ELETTRA in Trieste, the NPL and the University of Potsdam (Fig. 6). Antimicrobial peptides as effector molecules of the innate immune system are unique alternative drug candidates compared to conventional antibiotics.

Figure 7: Lateral distribution of the elements phosphorus, sulfur, chlorine, and potassium in pancreatic cancer tissue treated with radiotherapy (left) and untreated (center) as well as healthy pancreatic tissue (right) [Katja Frenzel, Working Group 7.24].

In the PTB laboratory at BESSY II, on the other hand, the performance of reference-free X-ray spectrometry for elemental analysis in the identification of cancer tissue was investigated by Working Group 7.24 within the framework of the EMIPR project RaCHy (Radiotherapy Coupled with Hyperthermia, Fig. 7). The EMPIR project MetVes II (Standardisation of concentration measurements of extracellular vesicles for medical diagnoses), in which Working Group 7.14 and 7.21 participated with measurements of Small-Angle X-ray Scattering (SAXS) for the characterization of reference particles, was successfully completed.

For non-contact body temperature measurements, a new standard was developed in Working Group 7.32, based on calculable temperature radiation from an ammonia heat pipe with an isothermally tempered aperture. In this context, a training video for the calibration of ear and forehead thermometers was produced in cooperation with Department 9.3 and PTB Media Design. This is intended to support developing countries, in particular in combating the COVID19 pandemic.

Figure 8: Workflow of the digital calibration services in the Vacuum Metrology Working Group. The central element is the database (framed), which contains various types of documents.
Figure 9: Calculated temperature maps for the cross-section of a GAMOR double resonator during filling with gas (upper row) and subsequent evacuation (lower row), shown as deviation from the mean temperature (29.765 °C).
Figure 10: Representation of the σ(7,3) and σ(0,8) orbitals of bisanthene (top) and Cu-metallised bisanthene (bottom) [Haags et al., Sci. Adv. 8, eabn0819 (2022)].

Digital transformation is also making its way into Division 7, for example in the management of vacuum calibrations. Together with Department 9.4, Working Group 7.54 Vacuum Metrology has presented a metrological quality infrastructure that takes full account of ISO 17025 with a workflow for customer calibrations of vacuum gauges (Fig. 8).

Most importantly, digital twins, numerical simulations and theoretical models are playing an increasing role in the development of measurement techniques, such as gas modulation refractometry (GAMOR) for measuring gas density and pressure in Working Group 7.55 and the influence of thermodynamic effects (Fig. 9). For photonic pressure measurement, ab-initio calculations at University College London on the line width of the water absorption line (201) 322-(000) 221 in the near infrared with three different Herriott cells were also confirmed.

Two DFG projects are also dedicated to numerical modeling. In the Bayesian Compressed Sensing project of Working Group 7.11, in cooperation with the departments 8.4 and 3.1 as well as the FU Berlin, the complete spectral data of spatially resolved Fourier transform spectroscopy in the infrared range were determined from a strongly reduced measurement data set of a sample by so-called low-rank reconstruction. The DFG project Fundamentals of Photoemission Tomography of the Working Group 7.13 with the Forschungszentrum Jülich and the University of Graz is concerned with numerical methods to infer the electron density distribution of the initial state from the momentum vector of photoelectrones. Recently, it has been possible to represent sigma orbitals that were previously inaccessible experimentally and whose changes are essential for understanding chemical processes (Fig. 10).

Figure 11: Calculated scattering curve of the cubic cloud of point-shaped scatterers (colored points) with the scattering volume as colored background. The electron microscope image (bottom left) confirms the cubic shape of the particles.

For the evaluation of measurements with Small-Angle X-ray Scattering (SAXS), Working Group 7.21 has developed the software Computing Debye's scattering formula for Extraordi-nary Formfactors (CDEF), which enables an approximate numerical calculation of SAXS scattering curves of arbitrarily shaped nanoparticles (Fig. 11). For the evaluation of quantitative X-ray spectrometry data, Working Group 7.24 uses the so-called OCEAN code and has published an experimental validation of calculated spectra for cyanates and thiocyanates as well as for titanium and titanium oxides in cooperation with NIST.

In order to improve the characterisation of complex semiconductor nanostructures, Working Group 7.14 has developed a hybrid measurement system and put it into operation in the PTB laboratory at BESSY II, which combines X-ray fluorescence spectroscopy and measurements of elastic scattering. For the evaluation, a numerical simulation of the experiments in the form of digital twins is just as necessary as reliable fundamental parameters.

Figure 12: The complex-valued refractive index n=1-δ-iβ of different materials for EUV lithography at a wavelength of 13.5 nm.

In this context, Working Group 7.13, together with partners from research and industry, has acquired a project for the development of optical materials for the vacuum-ultraviolet spectral range, in order to enable the traceability of ellipsometry measurements with laboratory equipment. Working Group 7.14 has established a generally available database for optical constants of relevant materials in the spectral range of extreme ultraviolet (EUV) radiation (Fig. 12). This spectral range, in particular, has become much more important due to the introduction of EUV lithography in semiconductor manufacturing.

The reference -free X-ray fluorescence analysis established in Working Group 7.24 at BESSY II is based on data especially for excitation cross sections and fluorescence yields. With this method, PTB is currently participating in an international intercomparison within the framework of the WIPANO standardization project KALIB-XRF, for which novel multi-element thin-film samples were designed, produced and pre-characterized with various analytical methods.

The metrological characterization of, in particular, complex composite materials (advanced materials) for applications in the fields of optics, semiconductor electronics, quantum technology, photovoltaics, energy storage, catalysis or biotechnology is also a central aspect in the preliminary version of a Conceptual Design Report (preCDR) for a future synchrotron radiation facility BESSY III in Berlin-Adlershof, which was presented to an international Project Advisory Committee (PAC) at HZB in September 2022. For the path to BESSY III, a BESSY II+ upgrade programme has also been developed for the next 10 years and reviewed by an international expert commission in October 2022, within the framework of which HZB and PTB also intend to jointly realize a new undulator beamline for materials metrology and, in particular, battery research in the tender X-ray spectral range.

For the preservation and expansion of PTB's worldwide leading position in the field of metrology with synchrotron radiation, a modern soft and tender X-ray synchrotron radiation source in Berlin-Adlershof is indispensable, complementary to PTB's own MLS for variable metrology operation at lower photon energies in the THz to EUV spectral range. In this context, an upgrade programme for the MLS has already been initiated with PTB-HZB special projects for the further development of a RF cavity based on semiconductor technology in 2021 as well as for the further development of electron beam diagnostics, the MLS control room and the orbit feedback system in 2022.

In this context, the continuous construction and expansion of measuring stations and the development of new measuring technology are also of great importance. The development of so-called Steady State Micro Bunching (SSMB) at the MLS in collaboration with Working Group 7.11 and 7.22, HZB and Tsinghua University in Beijing, for example, is extremely interesting for industry and research for the generation of pulsed coherent radiation of high average power. SSMB can now be well stabilized at the MLS via beam diagnostics in the THz spectral range. The corresponding detection system was optimized by a fast-switching Pockels cell.

Figure 13: Drawing of the new measuring station for VUV source calibration at the MLS.
Figure 14: The new EUV reflectometer at the MLS with lubricant-free vacuum mechanics.

For the new measuring station under construction for the calibration of VUV radiation sources at the MLS (Fig. 13), an integrating sphere suitable for wavelengths below 200 nm was constructed in Working Group 7.22 for the first time worldwide and is currently being manufactured. A plasma radiation source, also developed and calibrated in Working Group 7.22, was prepared and made available to the Max Planck Institute for Solar System Research (MPS) within the framework of a new research collaboration for the radiometric characterization of the EUVST (Extreme Ultraviolet High-Throughput Spectroscopic Telescope) of the planned Solar-C mission.

Working Group 7.13 has commissioned a new beamline at the MLS for services and research cooperation for detector radiometry and reflectometry at wavelengths between 40 nm and 400 nm. The new lubricant-free EUV reflectometer at the MLS, which can accommodate sample masses of up to 150 kg, meets the increased purity requirements of the industry partners of Working Group 7.12 (Fig. 14).

In 2022, the Working Group 7.12 was able to continue working on the industrial projects on EUV lithography (EUVL), especially at the MLS, despite the restriction of work possibilities due to COVID19 and a 6-month shutdown of the storage ring BESSY II. The cooperation partners exchanged views on current issues in EUVL metrology during a separate session on optical metrology at Photonics Days 2022. The very extensive cooperation with ASML, the world market leader in lithography steppers for the semiconductor industry, was extended for another five years.

In addition to the characterization of optical components for EUVL, the development of measurement methods for the characterization of complex nanoscale semiconductor structures now plays an important role. In this context, the two complementary X-ray methods GISAXS (Grazing Incidence Small-Angle X-ray Scattering) and GEXRF (Grazing Emission X-Ray Fluorescence analysis) were successfully compared in Working Group 7.21 and 7.14 on a chromium-coated, nanostructured TiO2 lattice.

The development and application of metrology for industry is, as it were, inherited by PTB and represents a central, overriding task, irrespective of current developments. This also applies to vacuum metrology in Working Group 7.54, where a new measuring station for the calibration of reference outgassing sources for dodecane and water was set up within the framework of a cooperation also on EUVL with ASML and Carl Zeiss in order to quantify contamination of vacuum components for EUVL systems. A newly developed ionization vacuum meter for the pressure range 10-6 Pa to 10-2 Pa from the EMPIR project 16NRM05 coordinated by PTB is now being produced by the company INFICON.

Figure 15: New THz reflection measuring head with optimised compact mechanical design.
Figure 16: Measuring station for the comparison of mid-infrared detectors.

Other metrological developments for industry relate to temperature sensors based on photonic microchips in Working Group 7.45 as part of the EMPIR project PhotOQuanT and to a THz reflection measuring head (Fig. 15) as part of the R&D cooperation project TeraMeTex (Terahertz (THz) measuring system for textile coatings) of Working Group 7.34.

Working Group 7.34 was also able to clarify the origin of inhomogeneities in power sensitivity via spatially resolved THz transmission and power measurements within the framework of the German-French R&D cooperation project SCAFT (Secure Communication at 6G Frequencies through Precise THz Power Measurements) funded by the Central Innovation Programme for SMEs (ZIM) of the Federal Ministry for Economic Affairs and Climate Action (BMWK). Working Group 7.33 has commissioned a comparative measuring station that allows the calibration of customer detectors in the mid-infrared range (Fig. 16).

The continuous establishment and expansion of measuring stations and the further development of metrology is central for the preservation of the top positions, in PTB as well as in Division 7, for applications in the field of metrological future topics, metrology with synchrotron radiation, and the many industrial cooperations as well as for the metrological fundamentals of all this.

In Working Group 7.33, for example, the secondary UV detector standards were calibrated for the first time with the radiation of a new compact and energy-efficient LDLS (Laser-Driven Light Source). In addition, the EQD (External Quantum Deficiency) of special induced-junction silicon photodiodes produced in this project was determined as part of the EMPIR project 18SIB10 chipS-CALe.

In Working Group 7.32, the procedure for measuring the emissivity of semi-transparent samples using analytical methods was optimized as part of a successfully completed doctoral thesis. In addition, the commissioning of a new Cs heat pipe cavity radiator closed the gap in the representation of the radiation temperature for the calibration of infrared cameras between 270 °C and 500 °C and significantly reduced the uncertainties. Finally, a modified laser flash facility now enables the measurement of the specific heat capacity on graphite-coated samples in Working Group 7.31.

Figure 17: Power factor (PF) of the new FeSi2-based reference material for thermoelectrics.

As part of the VIP+ project TESt-HT, which will be completed in September 2022, a reference material for the thermoelectric power factor (PF) was produced and metrologically characterized for the first time in collaboration with DLR Cologne on the basis of FeSi2 (Fig. 17). It serves as a benchmark in the temperature range between 300 K and 1000 K and thus covers the entire temperature range of currently investigated thermoelectric high-temperature materials.

In a cooperation with Leibniz IHP, Working Group 7.45 succeeded in realizing the high optical quality of ring resonators (Q-factor > 100 000) on the entire surface of an 8-inch wafer with more than 10 000 photonic structures. Also, based on the results of the EMPIR project EMPRESS 2, a calibration of optical thermometers based on sapphire fibre Bragg gratings was demonstrated here for the first time worldwide. In Working Group 7.42, in cooperation with Department 2.6, a cryo current comparator developed at PTB was used for measurements with resistance thermometers in order to be able to investigate relevant influence quantities in water triple point cells (title picture) with previously unattained accuracy and to reduce the uncertainties in primary thermometry above 0 °C.

Figure 18: Difference between thermodynamic and internationally agreed temperature (comparison of the new "Best Estimates" with the values from 2011).
Figure 19: Optical access of the flow test rig by means of laser Doppler velocimetry and filtered Brillouin scattering.

Below 0 °C, the deviations between the thermodynamic temperature T and the internationally agreed temperature T90 have been measured very accurately in recent years with considerably improved primary thermometers in Working Group 7.43 (Fig. 18). In the Working Group on Contact Thermometry of the Consultative Committee on Thermometry (CCT), more precise T/T90 values for the determination of thermodynamic temperatures with smaller uncertainty have now been defined under the leadership of PTB.

Also in Working Group 7.43, a new primary pressure standard was tested, which is based on capacitance measurements and ab initio calculations of the thermophysical properties of He-lium. With a relative uncertainty of about 2 ppm at 7 MPa in agreement with the world's best mechanical pressure standard (piston manometer in Department 3.3, uncertainty: 1 ppm), new possibilities for pressure metrology arise.

Finally, a new, non-invasive measuring principle was developed in a ZIM project on the topic of non-contact, highly accurate heat flow sensor for liquids, which simultaneously allows the determination of the volume flux via laser Doppler velocimetry and temperature via Brillouin scattering (Fig. 19).