Franklin Cho, University of Southern California
Electron paramagnetic resonance (EPR) spectroscopy has been widely applied to probe and study local structures and dynamic properties of various compounds in liquids and solids; for example, structures and dynamics in biological molecules, magnetic structures and relaxations in magnetic molecules, and quantum coherence in solid-state spin systems. High-frequency (HF) EPR spectroscopy is an emerging technique enabling finer spectral resolution, better absolute sensitivity, and improved time resolution. Here we present the development of a HF EPR and double electron-electron resonance (DEER) spectrometer at the University of Southern California [1]. The spectrometer consisting of a high-frequency high-power solid-state source, a quasioptical system, a phase-sensitive detection system, a 12.1 Tesla cryogenic-free superconducting magnet, and a 4He cryostat enables pulsed EPR/DEER measurements with a few hundred nanosecond pulses. We also discuss applications of the HF EPR/DEER spectrometer to study impurities in nanodiamonds. Existence of surface paramagnetic impurities in nanodiamonds is revealed by HF DEER and HF continuous-wave (cw) EPR measurements. Size dependence of longitudinal relaxation time T1 in nanodiamond powders is investigated by HF and X-band pulsed EPR spectroscopy.
[1] F. H. Cho, V. Stepanov and S. Takahashi, Rev. Sci. Instrum. 85, 075110 (2014).