Comparison results of sensing nqr using continuous wave and pulsed nqr - fft spectrometers

V.O. Khandozhko, A.P. Samila, L.F. Politansky

Yuriy Fedkovych Chernivtsi National University

Traditional continuous wave methods of observation of NMR and NQR is now almost completely superseded by pulse Fourier transform spectroscopy. Compared with the method of continuous frequency scanning, pulse Fourier transform spectroscopy has advantages, which consists in a high sensitivity, increased spectrum resolution, much less distortion of the lines shape. In addition, pulse spectroscopy provides a reduction in the time of observation compared with stationary methods.
The aim of the paper is to determine the effectiveness of assessment of output materials for photoelectronics by NQR hardware methods.
The comparison of the NQR spectra obtained by the method of continuous passage of the resonance lines and the pulse method with a fast Fourier transformation are performed in this paper. Research was done both on the nitrogen containing substance and the annealed GaSe and InSe crystals important for heterostructures production. Resonance of nitrogen 14N nuclei is in the low-frequency region (100 kHz – 5 MHz) and has a weak intensity, caused by small value of the quantum transitions energy. Obtained results indicate a higher resolution of NQR pulse spectroscopy in comparison with continuous spectroscopy.
Based on these experimental results it can be concluded that the same signal / noise ratio, methods of continuous frequency scanning and pulsed excitation provide identical results, but the shapes of resonance lines obtained using these methods are different.
In the pulse method there is a simultaneous response of all resonant transitions, i.e. it is recorded that response of nuclear induction over which the Fourier transform is made. In case of stationary technique – slow passage of resonance while maintaining a quasi-equilibrium nuclear spin excitation conditions is made at a single frequency. This leads to a decrease in the spectrometer sensitivity, so that the registration process is much longer. Application of NQR pulse method of fast Fourier transform for the study of layered semiconductors is more appropriate than the stationary method based on continuous frequency scanning in resonance area. Pulse method provides better spectra resolution, and also enables to determine a time of nuclear spin relaxation.
It was found that in both cases the spectra with the same values of the signal / noise ratio can be obtained, while in the pulse method the time of spectra determination is for an order of magnitude smaller compared with the method of continuous passage.