Probing Dynamics at Interfaces -
Options for Inelastic Neutron Reflectometry

Workshop PSI, July 4-6 2004

Scope of workshop

Dynamic phenomena in solid matter can show drastically different behaviour if the system dimensions are reduced. Diffusion and fluctuations in confined structures or at interfaces can be decreased by orders of magnitude, damped effectively changing the interaction with surrounding media, or even enhanced as found in low dimension magnetic structures. Up to now neutrons have been used to investigate the dynamics in such systems mainly by classical inelastic time of flight spectroscopy e.g. the analysis of water diffusion in layered systems, or by applying off-specular neutron reflectivity to elucidate fluctuations in layered systems such as polymer layers, smectic liquid crystals or phospholipid membranes.

The application of neutron reflectometry to study not only the structure and lateral organisation of layered systems and interfaces but also the dynamic features have been so far restricted mainly due to the low flux of current neutron sources. One possibility to do so, neutron spin echo reflectometry, which was originally presented already twenty years ago by Pynn, has gained new interest as an option to study the dynamic in layered systems and at interfaces (see recent work by Rekveldt, Pynn and Felcher). It was proposed to exploit Larmor precession techniques to extract dynamic information by neutron reflectometry and the feasibility of this approach was demonstrated in very recent work at HMI and ILL. In addition, a first neutron spin echo reflectometry like measurement of the dynamics in smectic liquid membranes has been done recently successfully on IN 15 at ILL. Furthermore, the principal possibility to perform neutron reflectometry measurements with a classical inelastic time of flight spectroscopy set-up was demonstrated some years ago in Dubna.

Inelastic neutron reflectometry would open up a complete new field in the analysis of dynamic phenomena by neutrons in various fields such as magnetic multilayers, polymer layers, biomembranes, solid-liquid interfaces and any interface related system. It would provide new and complementary information to methods like x-ray photoelectron correlation spectroscopy, EXAFS and NMR. Dedicated instruments for inelastic neuron reflectometry could be implemented within the planned instruments at the new neutron sources in the US and Japan and the second target station at ISIS and the current up-grading of instruments at ILL, HMI or PSI. Thus, the central part of the workshop will be the discussion of such instrument possibilities and experimental options for inelastic neutron reflectometry and its realization at current and future neutron sources.

The workshop will be open to any scientist interested to participate. No workshop fee will be collected. Presentations given by the invited participants will be published as workshop proceedings within an appropriate scientific journal.