Tip-based nanofabrication below 40 nm combined with a nanopositioning machine with a movement range of Ø100 mm. - In: Micro and nano engineering, ISSN 2590-0072, Bd. 19 (2023), 100201, S. 1-5
In this paper, the combination of an advanced nanopositioning technique and a tip-based system, which can be used as an atomic force microscope (AFM) and especially for field emission scanning probe lithography (FESPL) is presented. This is possible through the use of active microcantilevers that allow easy switching between measurement and write modes. The combination of nanopositioning and nanomeasuring machines and tip-based systems overcomes the usual limitations of AFM technology and makes it possible to perform high-precision surface scanning and nanofabrication on wafer sizes up to 4 in. We specifically discuss the potential of nanofabrication via FESPL in combination with the nanofabrication machine (NFM-100). Results are presented, where nanofabrication is demonstrated in form of a spiral path over a total length of 1 mm and the potential of this technique in terms of accuracy is discussed. Furthermore, ten lines were written with a pitch of 100 nm and a linewidth below 40 nm was achieved, which is in principle possible over the entire range of motion.
In situ, back-focal-plane-based determination of the numerical apertures in optical microscopes. - In: Applied optics, ISSN 2155-3165, Bd. 62 (2023), 3, S. 756-763
In this contribution, we present a technique for in situ determination of the numerical apertures (NAs) of optical microscopes using calibrated diffraction gratings. Many commonly practiced procedures use an external setup to determine the objective and condenser NAs. However, these values may become modified in the used microscope systems, e.g., by system intrinsic apertures. Therefore, in our improved technique, determination of the imaging NA is conducted in situ within the corresponding microscope at hand. Furthermore, the method has been extended to yield the microscope’s illumination NA as well. In total, we tested this procedure for determination of the imaging NA for four different microscope objectives with nominal values of 0.55 and 0.9, together with the illumination NAs for four different circular aperture diaphragms with diameters between 10 µm and 500 µm using several gratings of different pitches. All determined NA values agree essentially with their nominal values within their experimental uncertainties, but the uncertainties have been reduced by typically an order of magnitude as compared with the manufacturer’s specifications.
Stiffness considerations for a MEMS-based weighing cell. - In: Sensors, ISSN 1424-8220, Bd. 23 (2023), 6, 3342, S. 1-15
In this paper, a miniaturized weighing cell that is based on a micro-electro-mechanical-system (MEMS) is discussed. The MEMS-based weighing cell is inspired by macroscopic electromagnetic force compensation (EMFC) weighing cells and one of the crucial system parameters, the stiffness, is analyzed. The system stiffness in the direction of motion is first analytically evaluated using a rigid body approach and then also numerically modeled using the finite element method for comparison purposes. First prototypes of MEMS-based weighing cells were successfully microfabricated and the occurring fabrication-based system characteristics were considered in the overall system evaluation. The stiffness of the MEMS-based weighing cells was experimentally determined by using a static approach based on force-displacement measurements. Considering the geometry parameters of the microfabricated weighing cells, the measured stiffness values fit to the calculated stiffness values with a deviation from -6.7 to 3.8% depending on the microsystem under test. Based on our results, we demonstrate that MEMS-based weighing cells can be successfully fabricated with the proposed process and in principle be used for high-precision force measurements in the future. Nevertheless, improved system designs and read-out strategies are still required.
A GPS-referenced wavelength standard for high-precision displacement interferometry at λ = 633 nm. - In: Sensors, ISSN 1424-8220, Bd. 23 (2023), 3, 1734, S. 1-24
Since the turn of the millennium, the development and commercial availability of optical frequency combs has led to a steadily increase of worldwide installed frequency combs and a growing interest in using them for industrial-related metrology applications. Especially, GPS-referenced frequency combs often serve as a "self-calibrating" length standard for laser wavelength calibration in many national metrology institutes with uncertainties better than u = 1 × 10^-11. In this contribution, the application of a He-Ne laser source permanently disciplined to a GPS-referenced frequency comb for the interferometric measurements in a nanopositioning machine with a measuring volume of 200 mm × 200 mm × 25 mm (NPMM-200) is discussed. For this purpose, the frequency stability of the GPS-referenced comb is characterized by heterodyning with a diode laser referenced to an ultrastable cavity. Based on this comparison, an uncertainty of u = 9.2 × 10^-12 (τ = 8 s, k = 2) for the GPS-referenced comb has been obtained. By stabilizing a tunable He-Ne source to a single comb line, the long-term frequency stability of the comb is transferred onto our gas lasers increasing their long-term stability by three orders of magnitude. Second, short-term fluctuations-related length measurement errors were reduced to a value that falls below the nominal resolving capabilities of our interferometers (ΔL/L = 2.9 × 10^-11). Both measures make the influence of frequency distortions on the interferometric length measurement within the NPMM-200 negligible. Furthermore, this approach establishes a permanent link of interferometric length measurements to an atomic clock.
Ultralow expansion glass as material for advanced micromechanical systems. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 25 (2023), 9, 2201873, S. 1-14
Ultralow expansion (ULE) glasses are of special interest for temperature stabilized systems for example in precision metrology. Nowadays, ULE materials are mainly used in macroscopic and less in micromechanical systems. Reasons for this are a lack of technologies for parallel fabricating high-quality released microstructures with a high accuracy. As a result, there is a high demand in transferring these materials into miniaturized application examples, realistic system modeling, and the investigation of microscopic material properties. Herein, a technological base for fabricating released micromechanical structures and systems with a structure height above 100 μm in ULE 7972 glass is established. Herein, the main fabrication parameters that are important for the system design and contribute thus to the introduction of titanium silicate as material for glass-based micromechanical systems are discussed. To study the mechanical properties in combination with respective simulation models, microcantilevers are used as basic mechanical elements to evaluate technological parameters and other impact factors. The implemented models allow to predict the micromechanical system properties with a deviation of only ±5% and can thus effectively support the micromechanical system design in an early stage of development.
A feasibility study towards traceable calibration of size and form of microspheres by stitching AFM images using ICP point-to-plane algorithm. - In: Measurement science and technology, ISSN 1361-6501, Bd. 34 (2023), 5, 055009, S. 1-13
We present a new method for traceable calibration of size and form error of microspheres, which was realised by stitching a series of atomic force microscopic (AFM) images measured at different orientations of microspheres using the metrological large range AFM of the PTB. The stitching algorithm is achieved using an iterative closest point point-to-plane algorithm. As the AFM tip geometry is one of the most significant error sources for the developed method, it was traceably calibrated to a line width standard (type IVPS100-PTB), whose feature geometry was calibrated with a traceable route to the lattice constant of crystal silicon. Measurement setup, scan strategy, and data evaluation processes have been detailed in the paper. Measurement results show high stability and robustness of the developed method. For instance, the standard deviation of four repeated measurements reaches 5 nm, indicating promising performance.
Strahlungsfehler bei Lufttemperaturmessungen: Minimierung des Fehlers durch ein neues Referenzsystem und Vergleich mit konventionellen Messsystemen, Tages- und Jahresgang ihres Fehlers in Abhängigkeit von Strahlung und Windgeschwindigkeit :
Radiation error of air temperature measurements: minimization of the error by a new reference system and comparison with conventional measurement systems, diurnal and annual variation of their errors as a function of radiation and wind speed. - In: Technisches Messen, ISSN 2196-7113, Bd. 90 (2023), 1, S. 65-78
The measurement of air temperature is associated with inaccuracies resulting from radiation errors. Liquid thermometers and automatic sensors are therefore housed in screens. Mechanical ventilation also helps to increase the accuracy of readings. Nonetheless, temperature measurements are not completely accurate. This spurred the development of a measuring system that features improved radiation protection and a modified mechanical ventilation system through a new type of screen. Parallel measurements with this new measurement system and two conventional screens of multiple plastic cones were taken at a location in north-east Germany with a temperate climate. Of the two traditional screens, one was ventilated and the other not. Based on previous findings concerning the seasonality of radiation errors, our analysis of their dependency on global radiation and wind speed was focused on the months of May to August, when global radiation is at its strongest. It was found that the not insignificant differences in Δ T\Delta T display a characteristic diurnal variation. With the new measurement system, in comparison with the two conventional measurung systems, the average air temperature of the four surveyed months during daylight hours was 0.43 K and 0.58 K lower. The differences in Δ T\Delta T are greatest not in the middle of the day but when the sun is low in the sky, as radiation is then reflected into the screen. The findings contribute to the understanding of the temporal variability of radiation errors in modern weather stations in dependence on global radiation and wind speed. The technical innovations presented here allow radiation errors to be largely avoided.
Zur Massendynamik eines geschlossenen Ökosystems, gemessen mit einem Prototyp Vakuummassekomparator - eine methodische Validierungsstudie :
On mass dynamics in a closed ecological system, determined with a prototype vacuum mass comparator - a methodological validation study. - In: Technisches Messen, ISSN 2196-7113, Bd. 90 (2023), 2, S. 127-137
The aim of this work was to validate a novel methodology for high-resolution, repetitive measurements of mass dynamics of biological processes and structures in a closed plant-earth ecosystem consisting of Mammillaria vetula and microorganisms. To perform these experiments, the living system was materially welded into a newly developed Titanium Weighing Hollow Body (TWHB) with a laser. Three non-vital, also hermetically welded and high-vacuum suitable, externally identical TWHBs, filled with sand, served as controls. All TWHBs were equipped with a feedthrough and integrated light source. LEDs generated continuous light in all four bodies, which drove the photobiological processes in the vital test body and allowed long-term growth. Mass differences of the TWHBs were measured with a vacuum mass comparator at four points in time three months apart against two stainless steel mass standards. The expanded measurement uncertainty of the mass increase of the vital TWHB was calculated according to the Guide to the Expression of Uncertainty in Measurement (GUM) in each of the three independent experiments. The mass gain of the vital over the three nonvital TWHBs over the total experimental period of 9 months was +18 μg with the expanded measurement uncertainty 30 μg. The resulting mass gain would have had to be > 48 μg to be considered statistically significant with a confidence level of 97.7%; time intervals over three and six months were also not significant. The study validates for the first time a methodology capable of measuring mass dynamics of living matter over time, when statistically sound conclusions with measurement uncertainties in the microgram range are required. This opens up a new level of precision mass measurements, which makes the methodology a candidate, e.g., for the verification of the principle of mass conservation in the life-sciences.
Hysteresis associated with intrinsic-oxide traps in gate-tunable tetrahedral CVD-MoS2 memristor. - In: IEEE 22nd International Conference on Nanotechnology (NANO), (2022), S. 527-530
We introduce back gated memristor based on CVD-grown 30-40 nm thick MoS2 channel. The device demonstrates bipolar behaviour and the measurements are consistent with the simulations performed within the intrinsic-oxide traps model. This confirms the theory that the source of hysteresis in thin-film MoS2 memristors is charge trapping on MoS2/SiO2 interface and the grain boundaries. The impact of back gate voltage bias, voltage sweep range and channel area on memristive effect was studied and quantified using hysteresis area. Hysteresis in bipolar memristors can be tuned by back gate voltage, which makes these devices promising for neuromorphic computing.
Einsatz von gepulsten Lasern mit hoher Leistung in der Präzisionskraftmesstechnik - ein Schritt in die Richtung einer künftigen, SI-rückführbaren und praktischen Kraftquantisierung durch Photonenimpulse :
Deploying the high-power pulsed lasers in precision force metrology - towards SI traceable and practical force quantization by photon momentum. - In: Technisches Messen, ISSN 2196-7113, Bd. 89 (2022), 11, S. 757-777
Design and operational performance of table-top measurement apparatus is presented towards direct Planck constant traceable high accuracy and high precision small forces and optical power measurements within the SI unit system. Electromagnetic force compensation weighing balances, highly reflective mirrors and high-energy pulsed laser unit (static average power 20 W) are tailored together with a specially developed opto-electro-mechanical measurement infrastructure for cross-mapping the scale-systems of two different precision small force measurement methods. One of these methods obtains the force measurements by a state-of-the-art classical kinematic system employing the partial use of Kibble balance principle in the range of 10 nN to 4000 nN to be compared with forces generated due to quantum-mechanical effect namely the transfer of the momentum of photons from a macroscopic object. Detailed overview of the adapted measurement methodology, the static and the limits of dynamic measurement, the metrological traceability routes of the measurement parameters, quantities and their measurement uncertainties, parametric estimation of up (down)-scaling perspectives of the measurements are presented with respect to the state-of-the-art measurement principles and standard procedures within the newly redefined International System of Units (SI).