He, L.; Li, Chen W.; Hamilton, W. A.; Hong, T.; Tong, X.; Winn, B. L.; Crow, L.; Bailey, K.; Gallego, N. C.
Anomalous neutron scattering ‘halo’ observed in highly oriented pyrolytic graphite Journal Article
In: Journal of Applied Cyrstallography, 52 (2), pp. 296-303, 2019.
Abstract | Links | BibTeX | Tags: graphite, neutron scattering, phonon
@article{He2019,
title = {Anomalous neutron scattering ‘halo’ observed in highly oriented pyrolytic graphite},
author = {L. He and Chen W. Li and W.A. Hamilton and T. Hong and X. Tong and B.L. Winn and L. Crow and K. Bailey and N.C. Gallego},
url = {https://onlinelibrary.wiley.com/iucr/doi/10.1107/S1600576719001110},
doi = {10.1107/S1600576719001110},
year = {2019},
date = {2019-03-05},
journal = {Journal of Applied Cyrstallography},
volume = {52},
number = {2},
pages = {296-303},
abstract = {Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron ‘halo’ scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 A ̊ ). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed.},
keywords = {graphite, neutron scattering, phonon},
pubstate = {published},
tppubtype = {article}
}
Highly oriented pyrolytic graphite (HOPG) has been used as monochromators, analyzers and filters at neutron and X-ray scattering facilities for more than half a century. Interesting questions remain. In this work, the first observation of anomalous neutron ‘halo’ scattering of HOPG is reported. The scattering projects a ring onto the detector with a half-cone angle of 12.4, which surprisingly persists to incident neutron wavelengths far beyond the Bragg cutoff for graphite (6.71 A ̊ ). At longer wavelengths the ring is clearly a doublet with a splitting roughly proportional to wavelength. Sample tilting leads to the shift of the ring, which is wavelength dependent with longer wavelengths providing a smaller difference between the ring shift and the sample tilting. The ring broadens and weakens with decreasing HOPG quality. The lattice dynamics of graphite play a role in causing the scattering ring, as shown by the fact that the ring vanishes once the sample is cooled to 30 K. A possible interpretation by multiple scattering including elastic and inelastic processes is proposed.