Dynamic nuclear polarization requires a waveguide that connects the cold (1–10 K) sample space to the outside. To reduce the heating of the sample, a waveguide is produced from steel which has low thermal conductivity but attenuates the microwaves. Therefore, the inside of the waveguide should be plated with silver to reduce electrical losses. We show a new simple way to electroplate such waveguides with a thin silver layer and show that this improves the experimental performance.
The radio-frequency (rf) field amplitude in solid-state NMR probes changes over the sample volume, i.e. different parts of the sample will experience different nutation frequencies. If the sample is rotated inside the coil as it is typical for magic angle spinning in solid-state NMR, such a position-dependent inhomogeneity leads to an additional time dependence of the rf field amplitude. We show that such time-dependent modulations do not play an important role in many experiments.
Sample rotation around the magic angle averages out the dipolar couplings in homonuclear spin systems in a first-order approximation. However, in higher orders, residual coupling terms remain and lead to a broadening of the spectral lines. We investigate the source of this broadening and the effects on the powder line shape in small spin systems with and without chemical shifts. We show that one can expect different scaling behavior as a function of the spinning frequency for the two cases.
Resonant pulses in a spin-lock frame are used to select parts of the rf-field distribution in NMR experiments. Such pulses can be implemented in a straightforward way and arbitrarily shaped pulses can be used. We show an application of such pulses in homonuclear decoupling where restricting the amplitude distribution of the rf field leads to improved performance.
This paper analyzes a commonly used line-narrowing mechanism (homonuclear decoupling) in solid-state NMR and discusses what limits the achievable line width. Based on theoretical considerations, the contribution of different effects to the line width is discussed and a new contributing term is identified. This research allows us to evaluate new ways to improve the line width in such homonuclear decoupled spectra.
The NMR-MOUSE is a magnetic resonance tool for non-destructive materials testing inside a laboratory. The history and use of this sensor are reviewed with attention to issues encountered when employed outside. Improvements are outlined to facilitate outdoor measurements.
We have recently demonstrated the capability to rapidly spin spherical rotors inclined precisely at the magic angle (54.74°) with respect to the external magnetic field used for nuclear magnetic resonance (NMR) experiments. We show that it is possible to spin a spherical rotor without using turbine grooves and that these rotors are extremely stable because of the inherent spherical-ring geometry. These results portend the facile implementation of spherical rotors for solid-state NMR experiments.
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Through the advent of fast magic-angle spinning and high magnetic fields, the spectral resolution of solid-state NMR spectra has recently been greatly improved. To take full advantage of this gain, the magnetic field must be stable over the experiment time of hours or even days. We thus monitor the field by simultaneous acquisition of a frequency reference (SAFR) and use this information to correct multidimensional spectra improving resolution and availability of productive magnet time.
Through the advent of fast magic-angle spinning and high magnetic fields, the spectral...