0000000000361828
AUTHOR
Michael Eckardt
showing 5 related works from this author
How deprotonation changes molecular self-assembly – an AFM study in liquid environment
2013
We study the influence of Alizarin Red S deprotonation on molecular self-assembly at the solid-liquid interface of the natural cleavage plane of calcite immersed in aqueous solution. To elucidate the adsorption details, we perform pH dependent high-resolution atomic force microscopy measurements. When Alizarin Red S is deposited onto calcite(10.4) in a liquid environment at an acidic pH of 5, weakly bound, ordered islands with a (3 x 3) superstructure are observed. A sharp structural transition is revealed when increasing the pH above 8. Above this pH, stable needle-like structures oriented along the [01.0] direction form on the surface. Comparing these results with potentiometric titration…
Electron-driven spin diffusion supports crossing the diffusion barrier in MAS DNP
2018
Dynamic nuclear polarization (DNP) can be applied to enhance the sensitivity of solid-state NMR experiments by several orders of magnitude due to microwave-driven transfer of spin polarization from unpaired electrons to nuclei. While the underlying quantum mechanical aspects are sufficiently well understood on a microscopic level, the exact description of the large-scale spin dynamics, usually involving hundreds to thousands of nuclear spins per electron, is still lacking consensus. Generally, it is assumed that nuclear hyperpolarization can only be observed on nuclei which do not experience strong influence of the unpaired electrons and thus being significantly removed from the paramagneti…
High-precision measurement of the electron spin g factor of trapped atomic nitrogen in the endohedral fullerene N@C60
2018
Abstract The electronic g factor carries highly useful information about the electronic structure of a paramagnetic species, such as spin-orbit coupling and dia- or paramagnetic (de-)shielding due to local fields of surrounding electron pairs. However, in many cases, a near “spin-only” case is observed, in particular for light elements, necessitating accurate and precise measurement of the g factors. Such measurement is typically impeded by a “chicken and egg situation”: internal or external reference standards are used for relative comparison of electron paramagnetic resonance (EPR) Larmor frequencies. However, the g factor of the standard itself usually is subject to a significant uncerta…
Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization.
2017
We describe a frequency-agile gyrotron which can generate frequency-chirped microwave pulses. An arbitrary waveform generator (AWG) within the NMR spectrometer controls the microwave frequency, enabling synchronized pulsed control of both electron and nuclear spins. We demonstrate that the acceleration of emitted electrons, and thus the microwave frequency, can be quickly changed by varying the anode voltage. This strategy results in much faster frequency response than can be achieved by changing the potential of the electron emitter, and does not require a custom triode electron gun. The gyrotron frequency can be swept with a rate of 20 MHz/μs over a 670 MHz bandwidth in a static magnetic …
Stability of C60 and N@C60 under thermal and optical exposure
2015
N@C60, a nitrogen atom encapsulated in a fullerene shell, has an electron-nuclear spin system with outstanding coherence properties attractive for quantum computation. The stability of this molecule is known to be limited due to thermal escape of the nitrogen atom from the C60 cage but little is known about the stability towards optical excitation, which is one possible tool for an indirect scheme to manipulate and read out quantum information. Here, we report the results of a systematic study regarding thermal and optical effects on the stability of N@C60. The central result is that stability under intense laser irradiation can be obtained when the sample remains cooled below a certain tem…