Experimentelle Physik III

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http://hdl.handle.net/2003/42

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Untersuchungen zur Struktur und Dynamik von Festkörpern mit magnetischer Resonanzspektroskopie, hochauflösender Laserspektroskopie und Neutronenstreuung.

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Mobile-ion and matrix dynamics in dinitrile- and cycloalcohol-based lithium electrolytes studied by solid-state NMR, dielectric spectroscopy and rheology
(2024) Lansab, Sofiane; Böhmer, Roland; Schmidt, Claudia
Dinitrile-based lithium electrolytes were investigated through a comprehensive approach integrating nuclear magnetic resonance (NMR), dielectric spectroscopy, and viscosimetry. The reorientational motion within the succinonitrile-glutaronitrile (SN-GN) matrix was elucidated and the impact of lithium salt additions examined. Effect of enhanced molecular rigidity was investigated by incorporating fumaronitrile (FN) molecules with double central bond (C=C). Additionally, deuterated SN facilitated 2H NMR investigations of the reorientational dynamics, while 7Li NMR probed the charge carrier's dynamics. Viscosimetry, along with proton and lithium diffusion NMR measurements, offered insights interpreted via a paddle-wheel mechanism. Moreover, an exhaustive compilation and comparison of all available conductivity data for nitrile-based electrolytes was performed, with a specific focus on contextualizing the findings of this research. Ultimately, a comparative analysis was undertaken between the SN-GN matrix and an alternative hosting matrix comprised of cyclohexanol and cyclooctanol (HEX-OCT). This project involved dielectric spectroscopy and NMR investigations on various HEX-OCT-based electrolyte samples, expanding the approach employed for the SN-GN matrix on another substance class. In contrast to the dinitrile mixture, the HEX-OCT-based Li electrolytes were found to exhibit a revolving door mechanism, with volume effects playing a lesser role.
Anion dynamics and motional decoupling in a glycerol–choline chloride deep eutectic solvent studied by one- and two-dimensional 35Cl NMR
(2023-10-11) Hinz, Yannik; Beerwerth, Joachim; Böhmer, Roland
Chlorine-35 is among the few nuclides that provide an experimental handle on the anion dynamics in choline based deep eutectic solvents. By combining several nuclear magnetic resonance (NMR) techniques, the present work examines the Cl− motions within glyceline, a glycerol : choline chloride 2 : 1 solution, in a large temperature range down to the glass transition temperature Tg. The applied methods include spin relaxometry, second-order line shape analysis, as well as two-dimensional central-transition exchange and stimulated-echo spectroscopy. The finding of unstructured central-transition NMR spectra characterized by a relatively small average quadrupolar coupling attests to a highly disordered, essentially nondirectional anionic coordination in glyceline. For temperatures larger than about 1.3Tg the chlorine motions are well coupled to those of the glycerol and the choline moieties. At lower temperatures the local translational anion dynamics become Arrhenian and increasingly faster than the motion of glyceline's matrix molecules. Upon further cooling, the overall ionic conductivity continues to display a super-Arrhenius behavior, implying that the choline cations rather than the Cl anions dominate the long-range charge transport also near Tg.
Phenol, the simplest aromatic monohydroxy alcohol, displays a faint Debye-like process when mixed with a nonassociating liquid
(2023-09-01) Hoffmann, Lars; Beerwerth, Joachim; Moch, Kevin; Böhmer, Roland
Solvated in propylene carbonate, viscous phenol is studied using dielectric spectroscopy and shear rheology. In addition, several oxygen-17 and deuteron nuclear magnetic resonance (NMR) techniques are applied to specifically isotope labeled equimolar mixtures. Quantum chemical calculations are used to check the electrical field gradient at phenol's oxygen site. The chosen combination of NMR methods facilitates the selective examination of potentially hydrogen-bond related contributions as well as those dominated by the structural relaxation. Taken together the present results for phenol in equimolar mixtures with the van der Waals liquid propylene carbonate provide evidence for the existence of a very weak Debye-like process that originates from ringlike supramolecular associates.
Kernmagnetische und dielektrische Untersuchungen an wasserstoffbrückengebundenen Glasbildnern
(2024) Hoffmann, Lars; Böhmer, Roland; Vogel, Michael
Über polare OH-Gruppen bilden Moleküle häufig Wasserstoffbrückenbindungen zu ihren Nachbarmolekülen aus. Die Dynamik von wasserstoffbrückengebundenen Glasbildnern wird in dieser Arbeit an einem anorganischen Modellsystem, Wasser, und einem organischen Modellsystem, Phenol, analysiert. Hoch- und niederdichtes amorphes Eis werden mit der 17O-NMR untersucht. Die Linienform und die in der longitudinalen Spin-Relaxation kodierte Dynamik werden durch entsprechende Simulationen bzw. Spektraldichten beschrieben. Für kompaktiertes und poröses Amorphous Solid Water als weitere Modifikation von amorphem Eis wird der Einfluss der Porenstruktur auf die dielektrische Relaxation untersucht. Weiterhin werden wässrige Salzlösungen oft als Modelle für unterkühltes Wasser verwendet, weil Wasser und amorphes Eis stark zur Kristallisation neigen. In dieser Arbeit wird ein Salz gesucht, das NMR-Experimente an stark quadrupolar gestörten Kernen mit halbzahligem Spin ermöglicht. Alle untersuchten wässrigen Rubidiumsalzlösungen neigen zur Kristallisation; eine eutektische RbNO3-Lösung erweist sich als eingeschränkt geeignet. Wie Wasser ist auch Phenol schlecht unterkühlbar und ob wasserstoffbrückengebundene Netzwerke in Phenol existieren, war wegen der sterischen Hinderung des Phenylrings unklar. Durch Mischung mit Propylencarbonat gelingt es, Phenol in einem amorphen Zustand auf einen Debye-Prozess zu untersuchen. Mithilfe der 17O- sowie der 2H-NMR, der dielektrischen Spektroskopie und der Rheologie kann ein Dynamikbereich von mehr als zwölf Größenordnungen in der Korrelationszeit abgedeckt werden. Alle Experimente zeigen Hinweise auf einen schwachen Debye-Prozess, der dem Debye-Prozess von Monohydroxyalkoholen ähnelt.
Zero-field ODMR and relaxation of Si-vacancy centers in 6H-SiC
(2023-11-15) Singh, Harpreet; Anisimov, Andrey N.; Baranov, Pavel G.; Suter, Dieter
Silicon vacancies in silicon carbide (SiC) have been proposed as interesting candidates for quantum technology applications such as quantum sensing and quantum repeaters. SiC exists in many polytypes with different plane stacking sequences, and in each polytype, the vacancies can occupy a variety of different lattice sites. In this work, we focus on the three important charged silicon vacancies in the 6H-SiC polytype. We record the photoluminescence and continuous-wave optically detected magnetic resonance (ODMR) spectra at different radio-frequency power levels and different temperatures. We individually select the zero-phonon lines of the different silicon vacancies at low temperatures and record the corresponding ODMR spectra. ODMR allows us to correlate optical and magnetic resonance spectra and thereby separate signals from V1 and V3. The results also explain the observed sign change of the ODMR signal as a function of temperature.
High-field/high-frequency EPR spectroscopy in protein research: principles and examples
(2022-12-13) Möbius, Klaus; Savitsky, Anton
During the last decades, the combined efforts of biologists, chemists, and physicists in developing high-field/high-frequency EPR techniques and applying them to functional proteins have demonstrated that this type of magnetic resonance spectroscopy is particularly powerful for characterizing the structure and dynamics of stable and transient states of proteins in action on biologically relevant time scales ranging from nanoseconds to hours. The review article describes how high-field EPR methodology, in conjunction with site-specific isotope and spin-labeling strategies, is capable of providing new insights into fundamental biological processes. Specifically, we discuss the theoretical and instrumental background of continuous-wave and pulse high-field EPR and the multiple-resonance extensions EDNMR, ENDOR, TRIPLE, ESEEM, PELDOR, and RIDME. Some emphasis is placed on a balanced description of both the historical spadework and the achieved performance of advanced EPR at 95 GHz and 360 GHz. This culminates in a coherent treatment of state-of-the-art research of high-field EPR in terms of both instrumentation development and application to representative protein complexes such as cofactor binding sites in photosynthesis.
Single NV centers as sensors for radio-frequency fields
(2023-05-09) Zhang, Jingfu; Suter, Dieter
We show that a single electron spin can serve as a sensor for radio-frequency (rf) magnetic fields. The longitudinal and transverse components of the rf field can be extracted from the phase acquired during free evolution of the spin coherence. In our experimental demonstration, a single electron spin of an NV center in diamond serves as an atomic size of two components of an rf field.
Isotope effects on the dynamics of amorphous ices and aqueous phosphoric acid solutions
(2022-06-14) Ahlmann, S.; Hoffmann, L.; Keppler, M.; Münzner, P.; Tonauer, C. M.; Loerting, T.; Gainaru, C.; Böhmer, R.
The glass transitions of amorphous ices as well as of aqueous phosphoric acid solutions were reported to display very large 1H/2H isotope effects. Using dielectric spectroscopy, in both types of glassformers for equimolar protonated/deuterated mixtures an almost ideal isotope-mixing behavior rather than a bimodal relaxation is found. For the amorphous ices this finding is interpreted in terms of a glass-to-liquid rather than an orientational glass transition scenario. Based on calorimetric results revealing that major 16O/18O isotope effects are missing, the latter scenario was previously favored for the amorphous ices. Considering the dielectric results on 18O substituted amorphous ices and by comparison with corresponding results for the aqueous phosphoric acid solutions, it is argued that the present findings are compatible with the glass-to-liquid scenario. To provide additional information regarding the deeply supercooled state of 1H/2H isotopically mixed and 18O substituted glassformers, the aqueous phosphoric acid solutions are studied using shear mechanical spectroscopy as well, a technique which so far could not successfully be applied to characterize the glass transitions of the amorphous ices.
Small and Very Small Armed Aircraft and Missiles: Trends in Technology and Preventive Arms Control
(2023-03-01) Altmann, Jürgen; Suter, Dieter
The project ‘Preventive Arms Control for Small and Very Small Armed Aircraft and Missiles’ investigates the properties of ever smaller aircraft and missiles and explores possibilities for preventive arms control. The first part of this project report no. 3 covers the technological trends in both categories. (Further) miniaturisation is supported by civilian developments in mobile devices. Cheap production can allow swarms of very many uninhabited aerial vehicle (UAVs). Armed UAVs down to centimetre sizes and missiles down to 20 or 10 mm diameter are possible, with correspondingly very small destructive payloads. The second part assesses small and very small armed aircraft and missiles under criteria of preventive arms control. Both categories raise problems, mainly for international humanitarian law and military stability. Arms races have to be feared, increasing the threat of proliferation to non-state actors. Options for preventive limitations, confidence building and export control are presented. Recommended are prohibitions of autonomous attack and of swarms of autonomous armed systems, independent of size. If these are unattainable, limits should be established for quality and quantity of swarms; lower limits should be set for the size of armed UAVs and missiles; at a minimum numerical thresholds on the holdings of small and very small UAVs and missiles should be agreed on.
Hydrogen-bonded complexes of neutral nitroxide radicals with 2-propanol studied by multifrequency EPR/ENDOR
(2021-12-10) Savitsky, Anton; Nalepa, Anna; Petrenko, Taras; Plat, Martin; Möbius, Klaus; Lubitz, Wolfgang
The hydrogen bond plays a key role in weak directional intermolecular interactions. It is operative in determining molecular conformation and aggregation, and controls the function of many chemical systems, ranging from inorganic, organic to biological molecules. Although an enormous amount of spectroscopic information has been collected about hydrogen-bond formation between molecules with closed-shell electronic configuration, the details of such interactions between open-shell radicals and closed-shell molecules are still rare. Here we report on an investigation of hydrogen-bonded complexes between pyrroline-type as well as piperidine-type neutral nitroxide radicals and an alcohol, i.e., 2-propanol. These nitroxide radicals are commonly used as EPR spin labels and probes. To obtain information on the geometry of the complexes and their electronic structure, multi-resonance EPR techniques at various microwave frequencies (X-, Q-, W-band, 244 GHz) have been employed in conjunction with DFT calculations. The planar five-membered ring system of the pyrroline-type nitroxide radical was found to form exclusively well-defined in-plane σ-type hydrogen-bonded complexes with one 2-propanol molecule in the first solvation shell in frozen solution. The measured hyperfine parameters of the hydrogen-bridge proton and the internal magnetic parameters describing the electron Zeeman and the electron-nuclear hyperfine and nuclear quadrupole interactions are in good agreement with values predicted by state-of-the-art DFT calculations. In contrast, multi-resonance EPR on the non-planar six-membered ring system of the piperidine-type nitroxide radical (TEMPOL) reveals a more complex situation, i.e., a mixture of a σ-type with, presumably, an out-of-plane π-type complex, both present in comparable fraction in frozen solution. For TEMPOL, the DFT calculations failed to predict magnetic interaction parameters that are in good agreement with experiment, apparently due to the considerable flexibility of the nitroxide and hydrogen-bonded complex. The detailed information about nitroxide/solvent complexes is of particular importance for Dynamic Nuclear Polarization (DNP) and site-directed spin-labeling EPR studies that employ nitroxides as polarizing agents or spin labels, respectively.
Dielectric coupler for general purpose Q-band EPR cavity
(2021-08-19) Suter, Dieter; Savitsky, Anton; Judd, Martyna; Jolley, Greg; Cox, Nicholas
Here, we report on a robust and efficient mechanism for tuning the microwave coupling of a Q-band (34 GHz), general purpose, cylindrical EPR cavity operating in the TE011 mode. This novel mechanism allows for both the adjustment of the cavity’s coupling over a wide frequency range, as well as its bandwidth from that of a high-Q cavity (about 10 MHz), to a broadband cavity (above 1 GHz). The coupling element consists of a dielectric plate fixed onto a movable waveguide short that allows for two modes of operation. In the first mode, the dielectric plate does not influence the resonance properties of the coupling iris and allows for precise, critical coupling of the high-Q cavity. In the second mode, the dielectric plate is positioned in front of the coupling iris, varying the iris’ resonance properties and allowing very strong overcoupling to be achieved. This mechanism can be generalized for other types of EPR cavities, in particular at high microwave frequencies.
Mechanische und elektrische Eigenschaften von Ionenleitern
(2022) Ahlmann, Simon; Böhmer, Roland; Westphal, Carsten
The current global interest in energy storage has triggered the development of new composite materials and, consequently, new methodologies for manufacturing and testing these products. In the energy storage research field their mechanical behavior is less investigated, despite of their high both fundamental and technological relevance. To assess the interplay between charge and mass transport, this thesis focusses on a large variety of electrolytes using shear rheology and dielectric spectroscopy as examination methods. Tailoring the mechanical behavior of these materials, this work investigates the impact of their local and macroscopic viscoelasticity on their conductivity, with the ultimate goal of finding new recipes for improving the latter. Our investigations from a series of mixtures with an ionic liquid and a dipolar one shows an unusual shifting in the coupling between the mechanical and conductvity processes. A survey of ionogels demonstrate that the interaction of charge carriers with their gel-like matrix can affect conductivity even in the presence of a strong dynamical disparity between its macroscopic mechanical and electrical parameters. Finally, comparing ionic and proton conductors, it is shown that this decoupling significantly enhances the conductivity in acid hydrates. Our results and their analysis show that enhancing the degree of decoupling between the mechanical and electrical degrees of freedom, combined with a reduction of charge correlations in highly concentrated electrolytes are essential for the development of the next generation of energy storage materials.
Zentrallinien-NMR an stark quadrupolar gestörten Kernen in molekularen und ionischen Kristallen
(2022) Beerwerth, Joachim; Böhmer, Roland; Vogel, Michael
Dynamische Prozesse in molekularen und ionischen Kristallen werden mithilfe der Zentrallinien-NMR an den stark quadrupolar gestörten Kernen 11B und 17O untersucht. Dazu werden 11B-Relaxationszeiten in Orthocarboran gemessen und diese bezüglich der Moleküldynamik interpretiert. In Natriumnitrat wird der Dreiplatzsprung des planaren Nitrations mittels 17O-NMR untersucht. Diese Dynamik wird mit NMR-Spektren, stimulierte Echos und Relaxationszeiten untersucht. Mithilfe von Simulationen können aus gemessenen Spektren Sprungraten bestimmt werden. Ein 17O Hochtemperaturspektrum von Natriumnitrat wird mithilfe gemittelter Tensoren beschrieben. Die Reorientierungsdynamik in Natriumnitrat weist eine Aktivierungsenergie von EA = 0,38 eV auf. Als Beispiel für einen Tetraedersprung wird Kaliumpermanganat mithilfe der 17O-NMR untersucht. Hier wird mithilfe von stimulierten Echos eine Aktivierungsenergie von EA = 0,35 eV für die Sprünge der Sauerstoffatome bestimmt. Auch für Kaliumpermanganat werden die Relaxationszeiten gemessen und bezüglich der Reorientierungsdynamik interpretiert.
Survey of the Status of Small and Very Small Missiles
(2022-02) Altmann, Jürgen; Suter, Dieter
The project ‘Preventive Arms Control for Small and Very Small Armed Aircraft and Missiles’ investigates the properties of ever smaller aircraft and missiles. This project report no. 2 covers the status of missiles worldwide. Small and very small missiles are defined by diameter: below 69 mm and up to 40 mm, respectively. After an explanation of missile classes and typical properties, a short introduction into rocket propulsion and aerodynamics is given. A technical overview describes the components of a missile. A few example types are shown and potential military uses are discussed. The worldwide survey has resulted in a database that contains 50 types from 17 countries. The publicly available properties are given in 24 categories. Statistical evaluations cover several key parameters.
From ultraslow to extremely fast dynamics in sodium nitrate
(2020-05-28) Beerwerth, Joachim; Siegel, R.; Hoffmann, Lars; Plaga, Lucie S.; Storek, Michael; Bojer, B.; Senker, J.; Hiller, Wolf; Böhmer, Roland
Increasing dynamics in solids featuring nuclei subjected to second-order quadrupolar interactions lead to central-transition spectra that undergo two consecutive line-shaped transitions. Conventional motional narrowing occurs when the molecular exchange rate is on the order of the strength of the dominant interaction. In a second step, the resulting intermediately narrowed spectra change further when the motion becomes faster than the Larmor precession rate, leading to terminally narrowed spectra that can display a residual quadrupolar shift. We derive analytic expressions for this shift and analyze the quadrupolar central-transition spectra in terms of CN symmetrical cone models. Increasing the number of sites to N ≥ 3, the terminally narrowed spectra remain unaltered, while the intermediately narrowed spectra remain unaltered only for N ≥ 5. This finding relates to the different (cubic vs. icosahedral) symmetries that are required to average out the spatial second- and fourth-rank terms in the second-order quadrupolar interaction. Following recent work (Hung et al., Solid State Nucl Magn Reson 84:14–19, 2017), 17O NMR is applied to examine the three-site rotation of the nitrate group in NaNO3. Line shapes are measured and analyzed, and in addition to prior work, satellite-transition and stimulated-echo experiments are carried out. The final-state amplitudes extracted from the latter are reproduced using model calculations. It is shown how two-dimensional exchange spectra relating to N-site cone motions can be decomposed in terms of effective two-site-jump spectra. This latter approach is successfully tested for NaNO3.
Survey of the Status of Small Armed and Unarmed Uninhabited Aircraft
(2021-03-02) Pilch, Mathias; Altmann, Jürgen; Suter, Dieter
The project ‘Preventive Arms Control for Small and Very Small Armed Aircraft and Missiles’ investigates the properties of ever smaller aircraft and missiles. This project report no. 1 covers the status of aircraft worldwide, including relevant unarmed vehicles but excluding hobby aircraft. Small and very small aircraft are defined by size: below 2 m and below 0.2 m, respectively. After an elementary introduction into aerodynamics a technical overview is given, looking at airframe configurations, materials and manufacturing, power and propulsion, guidance, launch and recovery, and payloads. Future possibilities and trends are illustrated by presenting military research and development of the technological leader, the USA. Short chapters deal with swarms and with countermeasures. The worldwide survey has resulted in a database that contains 129 types from 27 countries. The publicly available properties are given in 26 categories. Statistical evaluations cover several key parameters.
Level anti-crossings of a nitrogen-vacancy center in diamond: decoherence-free subspaces and 3D sensors of microwave magnetic fields
(2020-10-30) Rao, K Rama Koteswara; Suter, Dieter
Nitrogen-vacancy (NV) centers in diamond have become an important tool for quantumtechnologies. All of these applications rely on long coherence times of electron and nuclear spinsassociated with these centers. Here, we study the energy level anti-crossings of an NV center indiamond coupled to a first-shell13C nuclear spin in a small static magnetic field. These levelanti-crossings (LACs) occur for specific orientations of the static magnetic field due to the strongnon-secular components of the Hamiltonian. At these orientations we observe decoherence-freesubspaces, where the electron spin coherence times (T∗2) are 5–7 times longer than those at otherorientations. Another interesting property at these LACs is that individual transition amplitudesare dominated by a single component of the magnetic dipole moment. Accordingly, this can beused for vector detection of microwave magnetic fields with a single NV center. This is particularlyimportant to precisely control the center using numerical optimal control techniques.
Efficient implementation of a quantum algorithm in a single nitrogen vacancy center of diamond
(2020-06-30) Zhang, Jingfu; Hegde, Swathi S.; Suter, Dieter
Quantum computers have the potential to speed up certain problems that are hard for classical computers. Hybrid systems, such as the nitrogen vacancy (NV) center in diamond, are among the most promising systems to implement quantum computing, provided the control of the different types of qubits can be efficiently implemented. In the case of the NV center, the anisotropic hyperfine interaction allows one to control the nuclear spins indirectly, through gate operations targeting the electron spin, combined with free precession. Here we demonstrate that this approach allows one to implement a full quantum algorithm, using the example of Grover's quantum search in a single NV center, whose electron is coupled to a carbon nuclear spin.
Optical detection of magnetic resonance
(2020-06-30) Suter, Dieter
The combination of magnetic resonance with laser spectroscopy provides some interesting options for increasing the sensitivity and information content of magnetic resonance. This review covers the basic physics behind the relevant processes, such as angular momentum conservation during absorption and emission. This can be used to enhance the polarization of the spin system by orders of magnitude compared to thermal polarisation as well as for detection with sensitivities down to the level of individual spins. These fundamental principles have been used in many different fields. This review summarises some of the examples in different physical system, including atomic and molecular systems, dielectric solids composed of rare earth and transition metal ions and semiconductors.
Application-specific microwave resonator development: addressing the challenges of modern electron paramagnetic resonance
(2020) Sidabras, Jason W.; Suter, Dieter; Lubitz, Wolfgang
Electron paramagnetic resonance (EPR) is a spectroscopic technique to study the interaction between free electrons and the local molecular environment. Over the past 60 years, EPR instrumentation and methodology has been developed to study, for example, the structure and dynamics of proteins, chemical reactions of organic-based radicals, transition-metal chemistry, catalytic reactions, electron transfer processes, and metalloenzymes. Because of these past developments, EPR has become a powerful tool for chemists and physicists alike. However, there remain several challenges in modern EPR that can be addressed by the development of application-specific microwave resonators. Three challenges are investigated: (i) improving the homogeneity of the magnetic flux density profile incident on a sample volume for applications to pulse EPR at Q-band frequencies (35 GHz); (ii) enhancing the sensitivity of EPR in the THz-bandgap (100 GHz to 1 THz frequency range; 3.34-33.36 cm1 energy range) to improve the detection of thin films with the use of a resonant meta-materials; and (iii) improving the absolute sensitivity at X-band frequencies (9.5 GHz) for the study of protein single-crystals with volumes less than 85 nl. First, the introduction of a uniform field re-entrant TE01U cavity at Q-band frequencies provides a 10 mm region-of-interest with a microwave field uniformity of 98%. The homogeneous field increases the microwave conversion factor by 60%. This design implements a waveguide H-type T-junction coupler with inductive obstacles to improve the coupling efficiency. The resonator is tested with a standard sample and shown to significantly improve the excitation profile for pulse EPR. Second, an investigation of the interaction between a split-ring resonator meta-material surface and a protein sample is presented as a way to increase the EPR signal for sub-THz frequencies. Data is collected using Frequency-Domain Fourier-Transform THz-EPR in the energy range of 11-18 cm1. The interaction of the EPR signal with a meta-material resonating at 14 cm1 is modeled with a lumped-circuit transmission-line. It was found that both inductive and capacitive coupling is required to fully understand this complex system. From this analysis, a factor of 4 in the EPR signal is shown for an active sample height of 24 m. Next, the absolute sensitivity at X-band frequencies has been increased up to a factor of 30 compared to commercial resonators by the implementation of a self-resonant micro-helix. This 0.4 mm inner diameter helix provides a resonator efficiency of 3.2 mT/W1=2 corresponding to a =2 pulse of 20 ns with an incident power of only 20 mW in a volume of 85 nl. This geometry is measured to have an absolute spin sensitivity of 64 106 Spins/G in 50 minutes of measurement time. Finally, the self-resonant micro-helix is used to obtain, for the first time, the angular dependence of the EPR signal from a protein single-crystal of [FeFe]-hydrogenase in the Hox state from Clostridium pasteurianum (CpI) with a volume of 3 nL. A signal-to-noise ratio of 290 was achieved for 4:25 109 spins in 8 minutes of measurement time. Full g-tensor analysis was successfully performed and an orientation of the principal axes is discussed. With the excellent signal-to-noise ratio, data was also collected on the same protein crystal using an ESEEM/HYSCORE pulse sequence. In total, this work pushes the state-of-the-art in EPR instrumentation allowing for new methodology development and broadening the applications available to chemists and physicists.

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