Evaluation of hysteresis response in achiral edges of graphene nanoribbons on semi-insulating SiC. - In: Materials science forum, ISSN 1662-9752, Bd. 1089 (2023), S. 15-22
Hysteresis response of epitaxially grown graphene nanoribbons devices on semi-insulating 4H-SiC in the armchair and zigzag directions is evaluated and studied. The influence of the orientation of fabrication and dimensions of graphene nanoribbons on the hysteresis effect reveals the metallic and semiconducting nature graphene nanoribbons. The hysteresis response of armchair based graphene nanoribbon side gate and top gated devices implies the influence of gate field electric strength and the contribution of surface traps, adsorbents, and initial defects on graphene as the primary sources of hysteresis. Additionally, passivation with AlOx and top gate modulation decreased the hysteresis and improved the current-voltage characteristics.
https://doi.org/10.4028/p-i2s1cm
Multipurpose active scanning probe cantilevers for near-field spectroscopy, scanning tunnel imaging, and atomic-resolution lithography. - In: Journal of vacuum science & technology, ISSN 2166-2754, Bd. 41 (2023), 4, S. 042601-1-042601-9
In this work, we report progress on developing a multipurpose scanning probe cantilever applying gallium nitride nanowires as the probe tip. Gallium nitride nanowires possess high potential as probes due to their straight profile, tunable electrical and optical properties, high Young’s Modulus, durability, and high-yield fabrication process. Their wide bandgap enables them to be pumped to emit ultraviolet pulses which can be used for optical imaging and spectroscopy. They can be doped during growth to be electrically conductive, and their sharp tips obtained during epitaxial growth enable confinement of a high electric field at tip-sample interface. Their sharp tips are obtained during fabrication by their epitaxial growth which eliminates the need for postprocess sharpening that is typically required for standard STM tips. We present results of using gallium nitride nanowires for scanning tunnel microscopy applications of atomic-resolution imaging and lithography, and atomic force microscopy applications of imaging and lithography in vacuum and atmospheric environments.
https://doi.org/10.1116/6.0002486
SI traceable small force generation and measurements via photon momentum. - In: SMSI 2023 Conference - Sensor and Measurement Science International, (2023), S. 133-134
In this contribution we present the concept of photon momentum enabled SI-traceably made small force generation and measurements below the conventionally accepted limits. The developed instrumentations, the measurement infrastructure and the obtained results demonstrate the advantages of this concept and further are extended to present the means of systematization of the force measurements covering the range below 10 μN to several tens of nN. The prospects to reduce the relative measurement uncertainties of small force and small weight measurements are discussed.
https://dx.doi.org/10.5162/SMSI2023/B7.1
Permanent tracebility of a nanopositioning and nanomeasuring machine. - In: 2023 ASPE Winter Topical Meeting: Precision Optical Metrology Workshop, (2023), S. 82-86
Due to the frequency stabilization of He-Ne-lasers directly to a frequency comb controlled by a GPS atomic clock disciplined oscillator and their direct coupling with a Nanopositioning and Nanomeasuring Machine, directly traceable measurements are demonstrated.
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.
https://doi.org/10.1016/j.mne.2023.100201
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.
https://doi.org/10.1364/AO.472223
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.
https://doi.org/10.3390/s23063342
Analytical description of transversally symmetrical hinges :
Analytische Beschreibung transversalsymmetrischer Gelenke. - In: Neunte IFToMM D-A-CH Konferenz 2023, (2023), insges. 2 S.
https://doi.org/10.17185/duepublico/77402
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.
https://doi.org/10.3390/s23031734
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.
https://doi.org/10.1002/adem.202201873