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Production sequence of Si-spheres and interferometrical determination of the sphere volume

Precision Engineering

Division 5

Micro- and nanopillars made of crystalline silicon and gallium nitride have been produced for PTB as reference artefacts for nanometrology. The aim of the work is to produce reference objects for nanomechanical and dimensional measurements to check and calibrate nanoindenters, atomic force microscopes and optical topography measuring instruments. First pillars with two diameters (0.5 μm and 0.7 μm) and five different heights from 0.5 μm to 11 μm were manufactured and characterized.

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In cooperation with the Center for Microtechnologies of the TU Chemnitz, a micro-opto-electro-mechanical force sensor with integrated tunable Fabry-Perot resonator was developed for measuring small forces with high resolution and a large measuring range. With this device it is also possible to determine the radiation pressure of lasers and thus to trace it back to a mechanical unit. First measurements of the radiation pressure of a semiconductor laser revealed a noise limitation of the micro force sensor of ~1 pN.

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The aim of the work is to investigate the influence of surface roughness on the determination of the indentation modulus and the indentation hardness of crystalline silicon samples. For this purpose, crystalline silicon samples with different roughness ranging from Sa = 5 nm to Sa = 54 nm were produced by reactive ion etching in cooperation with the Laboratory for Emerging Nanometrology (LENA) of Braunschweig Technical University. Both the surface roughness of all samples and the mechanical properties of the samples were measured.

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Die PTB hat sich in einem internationalen Vergleich von HfO2 Schichten auf Silizium mit einem Röntgenreflektometer (XRR) beteiligt. Die erste Auswertung des Vergleichs zeigt, dass 1.) die Werte aus XRR-Messungen der verschiedenen Teilnehmer eine hervorragende Übereinstimmung zeigen, und dass, 2.) sich aus der sorgfältigen Analyse und Kombination der Ergebnisse verschiedener Methoden systematische Abweichungen bestimmen lassen, und sich somit eine Schichtdickenbestimmung mit Referenzcharakter erreichen lässt.

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A new scanning electron microscope enabling ultimate resolution has been brought into service at PTB and will be used for research tasks and various calibration purposes. Amongst others, it will be applied for traceable measurements of the size distribution of nanoparticles as well as for dimensional measurements of nanostructures and film thickness. There are various detectors available enabling measurements in transmission and reflection as well as elemental analysis.

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In the frame of the EMPIR project “3DNano”, a new method for characterizing the tip form has been developed: The reference sample type “IVPS100-PTB“, jointly developed by the PTB and the company Team Nanotec and traceably calibrated using transmission electron microscopy is applied as tip characterizer. The reproducibility of the tip form of 20 repeated measurements reaches 0.4 nm.

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Quantitative investigation on the tip abrasion of diamond-like-carbon coated tips in a high-speed metrological large-range AFM device has been carried out on four surfaces made of silicon, niobium, aluminum and steel. The scanning speed was varied up to 1 mm/s and the vertical load forces were adjusted up to approximately 40 nN. The experimental results show that tip form changes abruptly rather than progressively. 

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In the frame of EMPIR project “NanoMag”, a new metrological large-range magnetic force microscope (Met. LR-MFM) has been set up based on the nanomeasuring machine (NMM), which has a measurement volume up to 25 mm x 25 mm x 5 mm. The developed instrument offers unique metrology capabilities of measuring samples from the nanoscale to the macroscale, and thus, it has the potential to bridge different magnetic field measurement tools having different spatially resolved scales.

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For the characterization of the shape and size of tactile probe tips a new standard was developed and fabricated in PTB using E-beam lithography and wet-chemical anisotropic silicon etching. The design consists of 10 x 28 grooves with a rectangular cross-section and a width varying from 0.3 – 3 µm. By scanning this pattern data can be obtained that can be used to reconstruct the shape and diameter of the probe tip.

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The Spatial Angle Autocollimator Calibrator (SAAC) of the PTB extends the calibration of autocollimators from plane to spatial angles up to 2500×2500 arcsec² and distances up to 1,8 m with a standard uncertainty of 7,5·10-3 arcsec. It is based on a Cartesian arrangement of the device under test and two reference autocollimators, which are oriented to a reflector cube.

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The coordinate metrology department has developed an internal microgear measurement standard that embodies 1 mm, 0.5 mm, 0.2 mm, and 0.1 mm modules (eight tooth spaces each). Two reference objects (carbide and titanium versions for computer tomography) were designed and manufactured in cooperation with the scientific instrumentation department. The tactile calibration on PTB’s micro coordinate measuring machine resulted in measurement uncertainties for profile and helix deviations ranging from 0.4 µm to 0.7 µm.

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The three-rosette method is the standard procedure for pitch calibration on gears. This method separates the pitch deviations of the gear from the deviations of the measuring machine. However, for a gear with n teeth, the method requires 2n2 measurements. A newly developed method requires much less measurements (starting from 10n), while the measurement uncertainty is only slightly higher. This was verified by an intercomparison.

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In February 2018 the inauguration of the Competence Center for Wind Energy (CCW) was celebrated. The novel building is equipped with a large coordinate measuring machine with a measurement volume of 5 m x 4 m x 2 m. The intended research activities within the area of dimensional metrology in this BMWi-funded research project aim at optimization of the measurement techniques for large drivetrain components of wind energy systems.

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In the EMPIR project MetAMMI, several additive manufacturing processes for the production of medical implants were assessed. For that, implants with complex geometry made of different materials (i.e. polymers, metal and ceramic) were evaluated at PTB. The results show that the overall geometry, material porosity and surface quality strongly depend on the additive manufacturing process used.

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The new measuring instrument “KOLD” serves for the traceability of outer and inner diameters as well as form of spheres, rings, cylinders, and gauge blocks in the field of coordinate metrology. KOLD is an interferometric Pseudo-Abbe comparator which consists of two form measuring machines with a shared rotary table, which allows to measure length and form in a single clamping. 

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The determination of task-specific measurement uncertainties is essential in industrial quality assurance. For this purpose, PTB, manufacturers, and users of coordinate measuring machines (CMMs) have developed the so-called “Virtual Coordinate Measuring Machine” (VCMM). In order to account for advancements in technology, the VCMM was refined, enhanced and verified in extensive comparison measurements.

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For calibrations with CMM the industry is claiming smaller and smaller measurement uncertainties. One of the main influences on the measurement uncertainty are guidance deviations. As part of a MNPQ project, a high accuracy CMM has now been equipped with a multi-beam interferometer, that detects the guidance deviations along the linear movement during a measurement and corrects the measured values online.

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Coordinate measuring machines (CMM) are prevailingly equipped with tactile probing 3D sensors. Progress in CMM technology allows to apply optical measuring as an alternative to tactile probes. Two different optical distance probes have been used on CMM for tests. Comparing measurements between optical and tactile probes on known standards with different optical surfaces has been done. Based on these measurements it is now possible to select suitable probes for the measuring tasks.

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Length measurements with highest accuracy require extremely stable conditions. Measurement instruments like the Geodetic Base of the PTB detect distortions over several minutes, e.g., when trains pass several hundred meters away. Such perturbations were studied in October 2017. Freight trains caused massive disturbance, while the impact of passenger trains seems to be manageable. The measurement results were covered by multiple media stations.

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The interferometric calibration of gauge blocks between 200 mm and 1000 mm length was previously only possible in the “Kösters interferometer” specially designed for this purpose. Due to the high demand, this service required a waiting period of up to six months. With the commissioning of a newly equipped second measuring device, calibration measurements can now be carried out in parallel, so that even lengthy calibrations of thermal expansion are no longer an obstacle.

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Electronic distance meters are commercially available with measurement ranges of up to over 100 m. They are very popular for craft or legal applications. The Eichamt Zwickau, a gauging office of Saxony, has set up a suitable, weather-independent and partially-automated reference baseline with a total length of 150 m in collaboration with PTB. This baseline will be used to check these instruments according to DIN ISO 16331-1 in future. PTB was strongly involved in the development of this standard.

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The PTB develops a technology to integrate thin-film technology components into workpieces fabricated by means of additive manufacturing. In this way, e.g. thermometers can be positioned in heat exchangers at the places of interest. Also, resistance strain gauges can be integrated in single- or multi-layered structures.

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