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Annual Report 2020

Division 7
Walther-Meißner-Bau in January 2021
Figure 1: Measuring instruments for non-contact determination of body temperatures and calibration curve.

The 2020 pandemic year also posed several challenges for Division 7 and in particular for the new management team established last year. But these were overcome through a high level of responsibility and commitment at all levels. In the field of international cooperation, it was even possible to support a number of developing and newly industrializing countries in building up measuring capacities and metrological standards for the non-contact determination of body temperatures (Figure 1).

With a home office ratio of more than 40 % on average since March 2020, the key figures of Division 7 nevertheless reached their usual high level, calibration revenues and third-party funding even reached new record levels. The Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) gratefully ensured the continuous operation of the Metrology Light Source (MLS) for measurements with synchrotron radiation, especially in the context of industrial collaborations on EUV lithography (EUVL).

An important basis for the continuous further development of optical measurement technology in the EUV spectral range is due to the cooperation between Department 7.1 and Carl Zeiss since 1998, which was extended in summer 2020 with the ninth addendum to continue until the end of 2024. With EUVL, PTB has for two decades been supporting a technology that was essentially developed in Germany and Europe, which has been used by the world's largest semiconductor producers for the manufacture of their high-end processors since 2019. Thus, it is also considered a technology driver for digital communication, the Internet of Things, e-commerce, Smart Home or Industry 4.0, and was awarded the German Future Prize by the Federal President in November 2020.

PTB's extensive cooperation with the EUVL industry will also be highlighted in the Conceptual Design Report (CDR) for the Berlin Photon Factory, which is currently being developed by HZB in close coordination with PTB. This will replace the two synchrotron radiation sources MLS and BESSY II in Berlin-Adlershof, currently used by PTB, in the years after 2030. A summary preliminary version of the CDR is to be presented to the responsible bodies in the Helmholtz Association and the ministries (BMBF, BMWi) in the course of 2021.

Nowadays, high-end semiconductor structures are in the range of only a few nanometers.  Semiconductor technology is thus nanotechnology, which is under the high pressure of constant further development, not only of production processes but also of suitable characterization methods. The contributions of PTB in Adlershof to this have therefore, long since no longer been limited to the characterization of EUVL projection optics, but also include the use of synchrotron radiation for the development of nanometrology methods. Examples are the EU project IT2 coordinated by the world market leader for EUVL systems, ASML, or a doctorate in Department 7.2 completed at the end of 2020 at TU Berlin titled: Using Grazing Incidence Small-Angle X-Ray Scattering (GISAXS) for Semiconductor Nanometrology and Defect Quantification.

With regard to the PTB topic area Nanometrology, the two Adlershof Departments 7.1 and 7.2 also cooperate very closely with other groups within and outside PTB. Examples are the reconstruction of 3D nanostructures with data from EUV scatterometry as well as reflectometry, small-angle scattering and fluorescence measurements in the X-ray range, currently along with Department 8.4, the University of Twente and the Kurchatov Institute in Moscow among others, the comparison of methods of traceable scattering and microscopy procedures with PTB Departments 4.2, 5.1 and 5.2, or measurements on ultra-bright quantum dots with the Federal Institute for Materials Research and Testing (BAM) within the framework of an EMPIR project.

Figure 2: Photoemission tomography (3D angle-resolved photoelectron spectroscopy, ARPES) to determine the orbital structure and aromaticity of Keculene [A. Haags et al., ACS Nano 2020, 14, 15766-15775].

In addition to EUV and X-ray radiation, softer spectral ranges are also used in the method development for nanometrology by Department 7.1 at the MLS. For example, an infrared near-field microscope was recently combined with a thermoelectric sample holder for spectroscopy of molecular fingerprints with nanometer resolution. In cooperation with the Forschungszentrum Jülich and the Karl-Franzens-Universität Graz, photoemission tomography in the vacuum UV spectral range (VUV) was used to detect the in-situ synthesis of Kekulene on a metal surface and to determine the structure of the molecular valence orbital (Figure 2).

Complex composite materials with nanoscale structures are often referred to as new materials or advanced materials and can be found in almost all fields of technology. With a nanostructure on the surface, for example, it was possible to reduce the reflection losses of a semiconductor photodiode, enabling a UV quantum yield of more than 130 % measured in Department 7.3. More generally, the structure and composition of new materials determine their mechanical, chemical, electronic, or optical properties and thus essentially their functionality, which requires sophisticated nanoanalytical measurement techniques.

Figure 3: X-ray scattering under grazing incidence (GIWAXS) in the PTB laboratory at BESSY II on a CsPbI1.8Br1.2 perovskite film [Al-Ashouri et al., Science 2020, 370, 1300-1309]

In the PTB laboratory at BESSY II, it was possible to characterize the crystal structure of perovskite solar cells using X-ray diffraction under grazing incidence (GIWAXS) as part of a collaboration between Department 7.2 and HZB (Figure 3). A new record in the overall efficiency for tandem cells of over 29 % was achieved. In connection with the development of novel energy materials, there is also a new DFG project with the TU Chemnitz and the University of Freiburg in the priority programme Polymer-based batteries, in which PTB is participating with high-resolution X-ray analytical in-operando measurements. With this work in the field of nanometrology, Adlershof's Department 7.2 also contributes to the PTB's cross-sectional topic Energy.

However, energy is primarily an issue in Division 7 at the Charlottenburg Campus, especially in Departments 7.4 and 7.5 with their core competences and responsibilities in the areas of temperature, heat, and vacuum. Thus, the combination of the latest PTB measurements with the dielectric constant gas thermometer (DCGT) and results from primary thermometers of other institutes made it possible to accurately determine the difference between thermodynamic temperature and the temperature corresponding to the International Temperature Scale ITS-90. For temperatures between 35 K and 200 K, the uncertainty was lowered by a factor of four.

To reduce the uncertainty of thermodynamic temperature measurements with gas thermometers themselves, theoretically calculated virial coefficients of helium in a wide temperature range were recently experimentally confirmed in Department 7.4. The investigation of the thermophysical properties of hydrogen, methane, and binary mixtures is in preparation, particularly with reference to the PTB hydrogen strategy. A measurement module developed for the benchmarking of different thermoelectric materials, which allows simultaneous measurements of the Seebeck coefficient and the electrical conductivity traceable to SI units, also represents a contribution of Department 7.4 to the PTB cross-sectional topic Energy.

Figure 4: Pressure measuring cell and sensor of the station for determining the speed of sound in seawater.
Figure 5: Design and realization of PTB's new blackbody for the World Infrared Standard Group (WISG) traceability at the Davos Physical Meteorological Observatory (PMOD).
Figure 6: Radiance standard for traceability of the Optical Ground Support Equipment (OGSE) at the Centre Spatial de Liege (CSL) to the PTB primary standard.

In contrast, the highly accurate measurement of the speed of sound in seawater as a function of pressure, temperature, and salinity as part of a doctoral project by Department 7.4 is used to record and model climate changes (Figure 4). However, in the Environment and Climate steering committee, Division 7 is essentially represented with expertise in the field of non-contact temperature measurement (radiation thermometry) and infrared earth remote sensing. Department 7.3 has developed and radiometrically characterized a new reference blackbody as part of the Baseline Surface Radiation Network (BSRN) for the measurement of atmospheric back radiation and for traceability by the World Infrared Standard Group (WISG) at the Davos Physical Meteorological Observatory (PMOD) (Figure 5).

Monitoring aerosols as one of the essential variables for climate models is the focus of the Multi-Viewing, Multi-Channel, Multi-Polarization Imaging Mission (3MI) of the EUMETSAT Polar System satellite program of the 2nd generation (2023 to 2037). To this end, Department 7.3 has used a novel radiance standard to trace the Optical Ground Support Equipment (OGSE) at the Centre Spatial de Liege (CSL) to the PTB primary standard (Figure 6) in the spectral range from 390 nm to 2170 nm. The quantitative investigation of atmospheric aerosol samples from field measurement campaigns with reference-free X-ray spectrometry is the subject of the EMPIR projects AEROMET and AEROMET II, which are coordinated in Department 7.2 and were successfully completed and launched, respectively, in 2020.

The contributions of Division 7 to PTB's cross-sectional topic Quantum Technology (QT) will be relocated to the Walther-Meißner-Bau (WMB), a new research building on the Charlottenburg Campus with highly specialized laboratory, measurement, and clean rooms on a usable floor space of 2,325 m2 (cover picture), opening in 2021. The development, fabrication, and application of superconducting quantum interference detectors (SQUID) in Department 7.6 for the measurement of smallest magnetic fields and currents at low temperatures is the main focus. However, Berlin’s contributions to the QT Center (QTZ) of PTB are also provided by the Charlottenburg Departments 7.4, 7.5, 7.3, and 8.2 and will be combined in the WMB.

Figure 7: DART prototype consisting of measurement amplifier (black box) and digitization stage (board on the right). On the left, the feed of a test signal into the amplifier input can be seen.

An application laboratory for QT applications in the millikelvin range is to be established at the WMB, combined with the expansion of existing networks with the TU Berlin, the companies Magnicon and Entropy housed at the WMB, and PTB Divisions 2, 4, 6, 7, and 8. For example, Department 7.6 is collaborating with Department 2.4 and partners from the Space Research Organisation Netherlands (SRON) and the National Institute of Advanced Industrial Science and Technology in Japan (AIST) in the new Horizon 2020 project AHEAD 2020 on the development of microwave SQUID multiplexers for high-sensitivity detection of particles and radiation by superconducting transition edge sensors (TESs). Departments 7.6 and 6.1 collaborate in the field of radionuclide spectroscopy and have developed a new statistical method for correcting energy spectra measured with highly sensitive metallic-magnetic calorimeters.

Noise thermometry, which is based on the thermal noise of a metal resistor, also represents a forward-looking field of work at the WMB. To combine noise thermometry as the primary method of measuring thermodynamic temperatures and classical resistance thermometry, Department 7.6 filed a patent application in 2020. This new concept of a dual-mode auto-calibrating resistance thermometer (DART, Figure 7) is particularly interesting for the industrially relevant temperature range from 77 K to 1000 K. With measuring stations of Division 7.4 in the WMB, it enables, for practical applications, direct connection to the redefined SI temperature scale.

Figure 8: Two versions with identical electro-optical design for a new ionization vacuum meter, manufactured by the companies INFICON (above) and VACOM (below).

Photonic thermometry also represents a quantum-based form of temperature measurement, based on the temperature dependence of optical material parameters such as the refractive index. In the EMPIR project PhotOQuant, Department 7.4 has developed a new generation of photonic microresonators for this purpose and integrated them in a combined design together with electrical sensors on a microstructured chip.

In the PTB steering committees for “Medicine” and “Digitization”, Division 7 is currently not yet represented, but provides contributions in terms of content. Thus, for vacuum metrology, Department 7.5 has integrated the generation of digital calibration certificates into the calibration workflow and has been issuing them on a test basis since September 2020.

In the field of vacuum metrology, furthermore, standardization is currently being prepared at ISO level for a novel ionization vacuum meter developed as a reference standard in EMPIR project 16NRM05. Here, the electrons pass through the ionization space on a straight path so that their path length and thus sensitivity can be well simulated (Figure 8).

Department 7.5 also successfully completed research work in 2020 on the new version of a European standard for thermal energy meters, which includes the use of water-glycol mixtures as a heat transfer medium, for example for use in solar thermal systems. For this purpose, a new test stand was set up to predict the measurement stability. Moreover, for the selection, installation, and operation of thermal energy measuring devices in the legally regulated area, standardized guidelines have been published in a technical report by the European Committee for Standardization with the significant contribution of Department 7.5.

Figure 9: Highly reflective films for concealment of insulation materials.

Legal metrology is one of the fundamental tasks of PTB. Apart from 7.5, this also concerns other departments in Division 7. For example, department 7.3 has investigated the emissivity of highly reflective foils used to minimize the thermal radiation loss of insulation materials within the framework of the recently completed EMPIR project EMIRIM (Figure 9). The results are now being incorporated into a European standard.

Department 7.6 has completed a project with Magnicon GmbH and Supracon AG in the funding program "Knowledge and Technology Transfer through Patents and Standards" (WIPANO), in which standardized terminologies, symbols and units for characteristic parameters of dc-SQUID sensors as well as measurement methods for their determination have been developed and tested. The project results were contributed to Working Group 14 "Superconducting Electronic Devices" of Technical Committee 90 "Superconductivity" of the International Electrotechnical Commission.

Department 7.2 has carried out a (partly inter-) national intercomparison on total reflection X-ray fluorescence analysis (TXRF) as part of a WIPANO standardization project, which represents an important contribution to updating DIN standard 51003 "Total reflection X-ray fluorescence analysis (TXRF) - General principles and terminology".

For 2021, key objectives of Division 7 relate to contributions to the CDR for the Berlin Photon Factory, the move to the Walther-Meißner-Bau, participation as an Associated Partner in the Climate Change Center Berlin-Brandenburg, the implementation of measures under the federal government's economic stimulus package, and the internal personnel development concept.