TilToF: A high-intensity space-time reflectometer

Being able to measure reflectivities down to 10−8 or 10−9 is the challenge of neutron reflectometers for the 21st century. The use of a periodic tilt of the sample, coupled with a position sensitive detector enables to perform specular reflectivity measurements on continuous neutron sources without any monochromator or chopper and thus allows intensity gains up to 10 compared to conventional reflectometers. The implementation consists in modulating the incidence angle of the beam by a periodic TilT of the sample of a few degrees at a frequency of the order of 20 Hz. At each time, the sample reflects the neutron white beam at a different angle. The reflected beam arrives at a different position on the detector. The time of flight (ToF) from the sample allows to separate the wavelengths, and as a result, the full reflectivity curve is measured in each detector cell. The duty cycle of such a reflectometer is only limited by the velocity of the sample movements and may exceed 90%. We present the first results obtained on a simplified setup (40% duty cycle) installed on the EROS reflectometer at the Laboratoire Léon Brillouin. This novel instrument provides the possibility to gain more than one order of magnitude in reflectivity which opens up the study of ultra-thin films (<2-3 nm).