05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Electrically detected magnetic resonance on a chip (EDMRoC) for analysis of thin-film silicon photovoltaics(2023) Segantini, Michele; Marcozzi, Gianluca; Djekic, Denis; Chu, Anh; Amkreutz, Daniel; Trinh, Cham Thi; Neubert, Sebastian; Stannowski, Bernd; Jacob, Kerstin; Rudolph, Ivo; McPeak, Joseph E.; Anders, Jens; Naydenov, Boris; Lips, KlausElectrically detected magnetic resonance (EDMR) is a spectroscopic technique that provides information about the physical properties of materials through the detection of variations in conductivity induced by spin-dependent processes. EDMR has been widely applied to investigate thin-film semiconductor materials in which the presence of defects can induce the current limiting processes. Conventional EDMR measurements are performed on samples with a special geometry that allows the use of a typical electron paramagnetic resonance (EPR) resonator. For such measurements, it is of utmost importance that the geometry of the sample under assessment does not influence the results of the experiment. Here, we present a single-board EPR spectrometer using a chip-integrated, voltage-controlled oscillator (VCO) array as a planar microwave source, whose geometry optimally matches that of a standard EDMR sample, and which greatly facilitates electrical interfacing to the device under assessment. The probehead combined an ultrasensitive transimpedance amplifier (TIA) with a twelve-coil array, VCO-based, single-board EPR spectrometer to permit EDMR-on-a-Chip (EDMRoC) investigations. EDMRoC measurements were performed at room temperature on a thin-film hydrogenated amorphous silicon (a-Si:H) pin solar cell under dark and forward bias conditions, and the recombination current driven by the a-Si:H dangling bonds (db) was detected. These experiments serve as a proof of concept for a new generation of small and versatile spectrometers that allow in situ and operando EDMR experiments.Item Open Access Monitoring the state of charge of vanadium redox flow batteries with an EPR-on-a-Chip dipstick sensor(2024) Künstner, Silvio; McPeak, Joseph E.; Chu, Anh; Kern, Michal; Dinse, Klaus-Peter; Naydenov, Boris; Fischer, Peter; Anders, Jens; Lips, KlausThe vanadium redox flow battery (VRFB) is considered a promising candidate for large-scale energy storage in the transition from fossil fuels to renewable energy sources. VRFBs store energy by electrochemical reactions of different electroactive species dissolved in electrolyte solutions. The redox couples of VRFBs are VO2+/VO2+ and V2+/V3+, the ratio of which to the total vanadium content determines the state of charge (SOC). V(iv) and V(ii) are paramagnetic half-integer spin species detectable and quantifiable with electron paramagnetic resonance spectroscopy (EPR). Common commercial EPR spectrometers, however, employ microwave cavity resonators which necessitate the use of large electromagnets, limiting their application to dedicated laboratories. For an SOC monitoring device for VRFBs, a small, cost-effective submersible EPR spectrometer, preferably with a permanent magnet, is desirable. The EPR-on-a-Chip (EPRoC) spectrometer miniaturises the complete EPR spectrometer onto a single microchip by utilising the coil of a voltage-controlled oscillator as both microwave source and detector. It is capable of sweeping the frequency while the magnetic field is held constant enabling the use of small permanent magnets. This drastically reduces the experimental complexity of EPR. Hence, the EPRoC fulfils the requirements for an SOC sensor. We, therefore, evaluate the potential for utilisation of an EPRoC dipstick spectrometer as an operando and continuously online monitor for the SOC of VRFBs. Herein, we present quantitative proof-of-principle submersible EPRoC experiments on variably charged vanadium electrolyte solutions. EPR data obtained with a commercial EPR spectrometer are in good agreement with the EPRoC data.Item Open Access Compact electron paramagnetic resonance on a chip spectrometer using a single sided permanent magnet(2024) Segantini, Michele; Marcozzi, Gianluca; Elrifai, Tarek; Shabratova, Ekaterina; Höflich, Katja; Deaconeasa, Mihaela; Niemann, Volker; Pietig, Rainer; McPeak, Joseph E.; Anders, Jens; Naydenov, Boris; Lips, KlausElectron paramagnetic resonance (EPR) spectroscopy provides information about the physical and chemical properties of materials by detecting paramagnetic states. Conventional EPR measurements are performed in high Q resonator using large electromagnets which limits the available space for operando experiments. Here we present a solution toward a portable EPR sensor based on the combination of the EPR-on-a-Chip (EPRoC) and a single-sided permanent magnet. This device can be placed directly into the sample environment (i.e., catalytic reaction vessels, ultrahigh vacuum deposition chambers, aqueous environments, etc.) to conduct in situ and operando measurements. The EPRoC reported herein is comprised of an array of 14 voltage-controlled oscillator (VCO) coils oscillating at 7 GHz. By using a single grain of crystalline BDPA, EPR measurements at different positions of the magnet with respect to the VCO array were performed. It was possible to create a 2D spatial map of a 1.5 mm × 5 mm region of the magnetic field with 50 μm resolution. This allowed for the determination of the magnetic field intensity and homogeneity, which are found to be 254.69 mT and 700 ppm, respectively. The magnetic field was mapped also along the vertical direction using a thin film a-Si layer. The EPRoC and permanent magnet were combined to form a miniaturized EPR spectrometer to perform experiments on tempol (4-hydroxy-2,2,6,6-teramethylpiperidin-1-oxyl) dissolved in an 80% glycerol and 20% water solution. It was possible to determine the molecular tumbling correlation time and to establish a calibration procedure to quantify the number of spins within the sample.Item Open Access Current trends in VCO-based EPR(2024) Kern, Michal; Chu, Anh; Anders, JensIn this article we provide an overview of chip-integrated voltage-controlled oscillator (VCO)-based EPR detection as a new paradigm in EPR sensing. After a brief motivation for this alternative detection method, we provide a self-contained overview of the detection principle, both for continuous-wave and pulsed detection. Based on this introduction, we will highlight the advantages and disadvantages of VCO-based detection compared to conventional resonator-based detection. This is followed by an overview of the current state of the art in VCO-based EPR and interesting emerging applications of the technology. The paper concludes with a brief summary and outlook on future research directions.Item Open Access Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina(2025) Kedia, Mayank; Das, Chittaranjan; Kot, Malgorzata; Yalcinkaya, Yenal; Zuo, Weiwei; Tabah Tanko, Kenedy; Matvija, Peter; Ezquer, Mikel; Cornago, Iñaki; Hempel, Wolfram; Kauffmann, Florian; Plate, Paul; Lira-Cantu, Monica; Weber, Stefan A. L.; Saliba, MichaelAtomic layer deposition of aluminum oxide (ALD-Al2O3) layers has recently been studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al2O3 layer acts as a protective barrier, mitigating pernicious halide ion migration from the perovskite towards the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (∼0.75 nm) ALD-Al2O3 layer that conformally coats the morphology of a triple-cation perovskite layer. This promotes an effective contact of the hole transporter layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC, we discovered that ALD-Al2O3 also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to these protective considerations, ALD-Al2O3 impedes the transition of crystalline perovskites to an undesired amorphous phase. Consequently, the dual functionality (i.e., enhanced contact and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1% to 20.5%, while retaining 98% of its initial performance compared to <10% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al2O3 as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs.Item Open Access Dead time-free detection of NMR signals using voltage-controlled oscillators(2023) Kern, Michal; Klotz, Tobias; Spiess, Maximilian; Mavridis, Petros; Blümich, Bernhard; Anders, JensIn this paper, we introduce voltage-controlled oscillators (VCOs) as a new type of nuclear magnetic resonance (NMR) detector, enabling dead time-free detection of NMR signals after an excitation pulse as well as the real-time inductive detection of Rabi oscillations during the pulse. Together with the theory of operation, we present the details of a custom-designed prototype implementation of a VCO-based NMR detector with an operating frequency around 62 MHz. The proof-of-concept measurements obtained with this prototype clearly demonstrate the possibility of performing dead time-free NMR experiments with coherent spin manipulation. Moreover, we also experimentally verified the capability of VCO-based detectors for performing real-time inductive detection of Rabi oscillations during the excitation pulse.