Neutron reflectometry examines the way in which surfaces or interfaces reflect neutrons in order to provide information on their organization, thickness, composition and roughness. Surface stacking can be studied on a depth of 1 to 300 nm (5 to 1500 atomic layers).
If the incident angle is lower than the critical angle, the material acts like a mirror and reflects all neutrons. If it is wider, only a part of neutrons are reflected. Measuring the proportion of reflected neutrons for a reflection angle equal to the incident angle makes it possible to explore the sample in a direction perpendicular to its surface. If measurement is made for different incident and reflecting angles, the sample is explored in its surface plane.