Is spin-echo resolved grazing incident scattering (SERGIS) useful to study dynamics at surfaces and interfaces?

Abstract

Surface excitations with energy ε and momentum q parallel to the surface can in principle be detected by neutron scattering. The issue is if spin-echo methods, widely used to detect low energy excitations in bulk, can also be used for detecting surface excitations. This issue comes at a time when spin-echo methods are proposed to resolve one of the components of neutron momentum transfer in near surface scattering (SERGIS). The conclusion is that no surface excitation can be measured with momentum perpendicular to the plane of specular reflection, i.e. when q _x  = 0. If q _x  ≠ 0, the observation of surface excitations is better carried out in an experiment in which spin-echo is used to resolve energy exchange for the measurement of the momentum transfer.

Keywords:

• Neutron inelastic scattering
• Spin-echo
• Scattering from surfaces

Acknowledgements

We would like to thank W. A. Hamilton for letting us reproduce figure 5 and R. Pynn for useful discussions. Work at Argonne was supported by the US DOE, Office of Science under contract #W-31-109-ENG-38. We thank the ILL for guaranteeing access to neutrons in the course of the feasibility tests described here. The “Focused Neutron Research” funding of the Max Planck Society made possible the design and acquisition of much of the instrumentation needed for the conversion of EVA.