The U.S. Dept. of Energy (DOE)’s Ames Laboratory is now the home to a dynamic nuclear polarization (DNP) solid-state nuclear magnetic resonance (NMR) spectrometer that helps scientists understand how individual atoms are arranged in materials. Ames Laboratory’s DNP-NMR is the first to be used for materials science and chemistry in the U.S.
To obtain this detailed information about materials’ structure and dynamics, solid-state NMR monitors the response of atomic nuclei to excitation with radio frequency waves.
“The frequency at which nuclei respond creates a unique spectral ‘fingerprint’ of their local environment within a material,” said Marek Pruski, Ames Laboratory’s lead scientist in solid-state NMR.
These “fingerprints” are especially useful in understanding the structure of non-crystalline materials—that is, materials that do not display regular crystalline structure amenable to diffraction studies. But, solid-state NMR is a challenging business. Because it operates at the low-energy end of the electromagnetic spectrum, the population difference between energy levels involved in NMR transitions is exceedingly small—only a few spins per million effectively generate the NMR signal.
In the last few years, several approaches involving ‘hyperpolarization’ of nuclear spins have emerged that are poised to revolutionize NMR spectroscopy. Chief among these is dynamic nuclear polarization (DNP). In short, DNP-NMR relies upon excitation of the unpaired electrons by microwave irradiation and subsequent transfer of the resulting spin polarization to the material’s nuclei, resulting in a much stronger response from these nuclei than is possible in conventional solid-state NMR.
“This instrument will allow us to improve the sensitivity by up to 100 times, and thus take data 10,000 times faster,” said Pruski.
Commercial DNP-NMR systems only became available in the last few years. Pruski and his Ames Laboratory colleague, Takeshi Kobayashi, collaborated with research groups in Europe to demonstrate how useful the DNP-NMR will be for materials research at Ames Laboratory.
“We have solid evidence that the DNP-NMR is a game-changing technique,” said Pruski. “Remarkably, DNP-NMR is still emerging. There’s great potential for its further development, and we are looking forward to making these advances. Most importantly, however, we want to use this new capability within several Ames Lab’s research programs to study complex metal hydrides, novel heterogeneous catalysts, biological nanocomposites, thermoelectrics and other energy-related materials.”
Source: Ames Lab