Pulsed-High Field/High-Frequency EPR Spectroscopy

230/115 GHz Electron Paramagnetic Resonance/Double Electron-Electron Resonance Spectroscopy

Electron paramagnetic resonance (EPR) and double electron-electron resonance (DEER) spectroscopies are powerful and versatile tools for studying local structures and dynamic properties of biological molecules. Similar to nuclear magnetic resonance (NMR) spectroscopy, EPR/DEER spectroscopies become more advantageous at higher frequencies and higher magnetic fields because of better spectral resolution as well as higher spin polarization. Here, we describe development of a high-frequency (HF) EPR/DEER spectrometer operating in the frequency range of 107-120 and 215-240 GHz and in the magnetic field range of 0-12.1 T, which has unique experimental capabilities such as enabling the complete spin polarization and wide-band DEER spectroscopy. Emphasis is given on the application of HF EPR/DEER techniques, and specific examples of HF EPR spectroscopy to drastically increase spin coherence in nanodiamonds as well as HF DEER spectroscopy to extract spin concentration in a diamond crystal are presented.

A high-frequency electron paramagnetic resonance spectrometer for multi-dimensional, multi-frequency, and multi-phase pulsed measurements

We describe instrumentation for a high-frequency electron paramagnetic resonance (EPR) and pulsed electron-electron double resonance (PELDOR) spectroscopy. The instrumentation is operated in the frequency range of 107-120 GHz and 215-240 GHz and in the magnetic field range of 0-12.1 T. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a cryogenic-free superconducting magnet, and a (4)He cryostat enables multi-frequency continuous-wave EPR spectroscopy as well as pulsed EPR measurements with a few hundred nanosecond pulses. Here we discuss the details of the design and the pulsed EPR sensitivity of the instrumentation. We also present performance of the instrumentation in unique experiments including PELDOR spectroscopy to probe correlations in an insulating electronic spin system and application of dynamical decoupling techniques to extend spin coherence of electron spins in an insulating solid-state system.