Room-Temperature Pulsed Dynamic Nuclear Polarization at 7 T

Abstract

Pulsed dynamic nuclear polarization (DNP) can enhance NMR signals by more than 2 orders of magnitude and is applicable to spin systems with short-lived electronic polarization. Recently, several pulsed DNP sequences were demonstrated at low magnetic fields. However, pulsed DNP at magnetic fields of modern NMR spectrometers (7 T and above) necessitates addressing major technical challenges for generating sufficiently high mm-wave B_1e amplitudes to match the nuclear Larmor frequencies. Here we describe a first-of-its-kind ESR/NMR spectrometer for pulsed DNP and phase-sensitive electronic detection operating at 7 T magnetic field. Generation of B_1e fields with amplitudes of ca. 75 MHz was made possible by employing a pulsed extended interaction klystron and piezo-tunable photonic-band gap resonators with unloaded quality factors Q ≈ 1500. Room-temperature NOVEL DNP yielded natural-abundance ¹³C NMR signal gains of up to 800 for a 30 μm thick crystal of a synthetic diamond. Simultaneous coherent manipulation of the electronic and nuclear spins was demonstrated by ¹³C-detected electron Rabi nutations.