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

Abstract

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 (T₁ = 11 μs, T₂ = 3.3 μs), 0.2% N@C₆₀ solid (T₁ = 120–160 μs, T₂ = 2.8 μs) and neutral single substitutional nitrogen centres (N_S⁰) in diamonds (T₁ = 2300 μs, T₂ = 230 μs). 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, T₂^* (∼ 10 ns) is too short to perform FTEPR. For 0.2% N@C₆₀, the signal-to-noise ratio for rapid scan is about five times better than for FTEPR. For N_S⁰ the signal-to-noise ratio is similar for rapid scan and FTEPR.

Keywords:

• rapid-scan EPR
• hydrogenated silicon
• N@C₆₀
• single substitutional N in diamond

Acknowledgements

This work was supported in part by NSF IDBR 0753018 (SSE and GRE) and by an NSF Graduate Fellowship to DGM. AS gratefully acknowledges financial support from BMBF (EPR-Solar network project 03SF0328). The sample of N@C₆₀ was graciously provided by Prof Aharon Blank, Technion, Israel. We thank Drs Sonya Calnan and Bernd Stannowski (Competence Centre Thin-Film- and Nanotechnology for Photovoltaics Berlin) for providing the a-Si:H sample. Joshua Biller (University of Denver) collected some of the preliminary inversion recovery and spin echo decay T₁ and T₂ measurements for the a-Si:H sample.