Application of precise neutron focusing mirrors for neutron reflectometry: latest results and future prospects

Neutron reflectometry (NR) is a powerful tool for providing insight into the evolution of interfacial structures, for example via operando measurements for electrode–electrolyte interfaces, with a spatial resolution of nanometres. The time resolution of NR, which ranges from seconds to minutes depending on the reflection intensity, unfortunately remains low, particularly for small samples made of state‐of‐the‐art materials even with the latest neutron reflectometers. To overcome this problem, a large‐area focusing supermirror manufactured with ultra‐precision machining has been employed to enhance the neutron flux at the sample, and a gain of approximately 100% in the neutron flux was achieved. Using this mirror, a reflectivity measurement was performed on a thin cathode film on an SrTiO3 substrate in contact with an electrolyte with a small area of 15 × 15 mm. The reflectivity data obtained with the focusing mirror were consistent with those without the mirror, but the acquisition time was shortened to half that of the original, which is an important milestone for rapid measurements with a limited reciprocal space. Furthermore, a method for further upgrades that will reveal the structural evolution with a wide reciprocal space is proposed, by applying this mirror for multi‐incident‐angle neutron reflectometry. A large‐area focusing supermirror manufactured with ultra‐precision machining has been employed at the SOFIA reflectometer at the J‐PARC Materials and Life Science Experimental Facility, and a gain of approximately 100% in the neutron flux was achieved. For future upgrade, optics using the focusing mirror for multi‐incident‐angle neutron reflectometry are proposed, in order to reveal evolutions of interfacial structures for operando measurements with a wide reciprocal space.