Sputtered multilayers are used as neutron optical elements in a wide variety of applications. The weak points in the present technology are the limited angular or energy range and the appearance of diffuse scattering. In order to produce better multilayers means that their total thickness and the quality of the interfaces have to be enhanced. The limiting factor for the total thickness of the supermirror is in-plane stress; hence strategies have to be developed to suppress its formation during the deposition. By a good quality of interfaces for neutron optics one understands a smooth and sharp change in the scattering length density. Smooth means that there is no lateral modulation (roughness), which leads to a reduction of the reflectivity and an increase of diffuse scattering. In many cases ideal interfaces cannot be realised. In these cases our strategy will be to control or induce interdiffusion in order to obtain diffuse but smooth interfaces. The reflectivity then is still decreased, but diffuse scattering is suppressed.

For certain applications such as monochromators this even opens the new possibility to design coatings with a sinusoidal scattering-length density with the consequence that no higher harmonics will be reflected. Since, at the time being, computer codes for the calculation of layer sequences are based on the concept of sharp interfaces, new formalisms will be developed to pay respect to this fact.

These innovations will allow us to design and to produce supermirrors with larger angular range (m > 4), and monochromatos where higher harmonics are suppressed. In addition, multilayer coatings with laterally graded layer-thickness will be produced for devices changing the divergence of the neutron beam, for example in phase space transformers.

Results
In order to realise large gains in intensity, introducing intermediate layers in artificial multilayers has improved the quality of the coatings. E.g. making the interfaces more diffuse allows for decreasing the roughness and reducing the contribution of higher order reflections.
A monochromator with diffuse interfaces is already in use at the neutron reflectometer NARZISS at SINQ and may be installed at other beam lines in the near future.