A sensitivity leap for X-band EPR using a probehead with a cryogenic preamplifier.

Simenas M, O'Sullivan J, Zollitsch CW, et al. A sensitivity leap for X-band EPR using a probehead with a cryogenic preamplifier. Journal of magnetic resonance. 2020;322: 106876.Inspired by the considerable success of cryogenically cooled NMR cryoprobes, we present an upgraded X-band EPR probehead, equipped with a cryogenic low-noise preamplifier. Our setup suppresses source noise, can handle the high microwave powers typical in X-band pulsed EPR, and is compatible with the convenient resonator coupling and sample access found on commercially available spectrometers. Our approach allows standard pulsed and continuous-wave EPR experiments to be performed at X-band frequency with significantly increased sensitivity compared to the unmodified setup. The probehead demonstrates a voltage signal-to-noise ratio (SNR) enhancement by a factor close to 8* at a temperature of 6K, and remains close to 2* at room temperature. By further suppressing room-temperature noise at the expense of reduced microwave power (and thus minimum pi-pulse length), the factor of SNR improvement approaches 15 at 6K, corresponding to an impressive 200-fold reduction in EPR measurement time. We reveal the full potential of this probehead by demonstrating such SNR improvements using a suite of typical hyperfine and dipolar spectroscopy experiments on exemplary samples. Copyright © 2020 Elsevier Inc. All rights reserved