London Centre for Nanotechnology, University College London, London WC1H 0AH, UK.
London Centre for Nanotechnology, University College London, London WC1H 0AH, UK.
J Magn Reson. 2021 Jan;322:106876. doi: 10.1016/j.jmr.2020.106876. Epub 2020 Nov 17.
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 6 K, and remains close to 2× at room temperature. By further suppressing room-temperature noise at the expense of reduced microwave power (and thus minimum π-pulse length), the factor of SNR improvement approaches 15 at 6 K, 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.
受低温冷却 NMR 探头取得巨大成功的启发，我们设计了一种升级的 X 波段 EPR 探头，配备了低温低噪声前置放大器。我们的设计抑制了源噪声，可以处理 X 波段脉冲 EPR 中常见的高微波功率，并且与商用光谱仪上方便的谐振器耦合和样品访问兼容。我们的方法允许在 X 波段频率下进行标准的脉冲和连续波 EPR 实验，与未修改的设置相比，灵敏度显著提高。该探头在 6 K 的温度下，电压信噪比（SNR）提高了近 8 倍，在室温下仍接近 2 倍。通过进一步抑制室温噪声，牺牲微波功率（从而最小化 π 脉冲长度），在 6 K 时 SNR 提高的倍数接近 15，相当于 EPR 测量时间减少了 200 倍。我们通过在典型的超精细和偶极子光谱实验套件上对示例样品进行演示，展示了这种探头的全部潜力。
