X-band rapid-scan EPR of samples with long electron spin relaxation times: a comparison of continuous wave, pulse and rapid-scan EPR

X-band room temperature spectra obtained by rapid-scan, continuous wave, field-swept echo-detected and Fourier transform electron paramagnetic resonance (FTEPR) were compared for three samples with long electron spin relaxation times: amorphous hydrogenated silicon (T-1 = 11s, T-2 = 3.3s), 0.2% N@C-60 solid (T-1 = 120-160s, T-2 = 2.8s) and neutral single substitutional nitrogen centres (N-S(0)) in diamonds (T-1 = 2300s, T-2 = 230s). For each technique, experimental parameters were selected to give less than 2% broadening of the lineshape. For the same data acquisition times, the signal-to-noise for the rapid-scan spectra was one-to-two orders of magnitude better than for continuous wave or field-swept echo-detected spectra. For amorphous hydrogenated silicon, T-2(*) (approximate to 10ns) is too short to perform FTEPR. For 0.2% N@C-60, the signal-to-noise ratio for rapid scan is about five times better than for FTEPR. For N-S(0) the signal-to-noise ratio is similar for rapid scan and FTEPR.