Atomically Smooth Surfaces as Substrates for Advanced Neutron Supermirrors

Neutron scattering facilities are a key resource aiding the diverse and growing revolution in nano-science and technology. An ongoing challenge for these facilities is providing sufficient neutron flux for an acceptable signal-to-noise ratio for ever more precise experiments. Presently much of the neutron flux is lost because of inefficiencies in the hundreds of meters beam guides and other optics that are used to transport the neutron from the source to the experiments. Reflecting and focusing neutrons requires optical surfaces that are smooth to the level of atomic dimensions (1 Å). This level of smoothness is extremely difficult, time- consuming, costly, and often impossible to achieve using conventional mechanical polishing methods, particularly when smoothing the metallic substrates and the 3-demensionally curved surfaces that are most desired for this application. The goal of our project is to apply new surface smoothing technologies to improve the performance of neutron optics. In phase l we investigated two innovative, new, surface nano-smoothing technologies based on using high- energy, focused beams of nanoscale cluster ions to bombard a surface for the critical final smoothing steps required to produce the desired atomically-smooth surface finish. As a demonstration we manufactured flat m=3 neutron supermirrors on glass substrates. These will be evaluated soon using neutron reflectometry. In phase ll we will investigate the smoothing capability of these technologies for novel metallic substrate materials and for curved surfaces, and then we will demonstrate their performance by producing an advanced neutron optic for Oak Ridge National Laboratories’ neutron scattering facilities. The planned optic can be used upstream of an experimental station to reduce the spot size of the neutron beam to accommodate the use of small samples and high-pressure cells. These innovative polishing methods will allow more capable, quicker to manufacture and less expensive neutron optics for use at the many neutron scattering centers that are now operating or are under construction worldwide.