The apparatus for multioptional reflectometry (AMOR) at SINQ/PSI is a versatile reflectometer operational in the time-of-flight (TOF) mode (in a wavelength range of 0.15 nm < λ < 1.3 nm) as well as in the monochromatic (θ-2θ) mode with both polarized and unpolarized neutrons. AMOR is designed to perform reflectometry measurements in horizontal sample-plane geometry which allows studying both solid-liquid and liquid-liquid interfaces. A pulsed cold neutron beam from the end position of the neutron guide is produced by a dual-chopper system (side-by-side) having two windows at 180 • and rotatable with a maximum frequency of 200 Hz. In the TOF mode, the chopper frequency, width of the gating window and the chopper-detector distance can be selected independently providing a wide range of q-resolution (∆ q/q = 1-10%). Remanent FeCoV/Ti : N supermirrors are used as polarizer/analyzer with a polarization efficiency of ∼97%. For the monochromatic wavelength mode, a Ni/Ti multilayer is used as a monochromator, giving ∼50% reflectivity at a wavelength of 0.47 nm. In the present work, a detailed description of the instrument and setting-up of the polarization option is described. Results from some of the recent studies with polarized neutrons and measurements on liquid surfaces are presented.

Amorphous silicon is a high-capacity negative electrode material for use in advanced lithium-ion batteries. We investigated the mechanism of Li incorporation into and removal from this material during electrochemical lithiation and delithiation using a combination of in operando neutron reflectometry and ex situ secondary ion mass spectrometry. The results indicate that a heterogeneous lithiation mechanism is present for the first cycle and also for subsequent cycles during lithiation and delithiation, where a highly lithiated phase penetrates the silicon electrode. During the first lithiation half-cycle, a two-step process takes place, which is not present for delithiation and higher cycles. In the first step, a Li-poor phase penetrates the silicon electrode leading to about 10% of maximum capacity. Afterward, during the second step, a Li-rich phase moves into the electrode leading to complete lithiation in a slower process. The different phases are separated by a relatively sharp interface of only several nanometers. The Li-poor phase extended over the entire electrode is still present after delithiation in the form of irreversibly trapped Li.

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Structure and dynamics of silicon-oxygen pairs and their role in silicon self-diffusion in amorphous silicaNeutron reflectometry and isotope multilayers were used to investigate self-diffusion in covalent amorphous solids during isothermal annealing and its correlation to structural relaxation. Amorphous silicon nitride was chosen as a model system. Neutron reflectometry is a superior method to measure very low self-diffusivities, occurring in covalent solids, by applying only short time anneals. This allows one to determine time dependent changes of diffusivity over a broad temperature range before crystallization of the metastable solid occurs. The measured nitrogen diffusivities decrease by more than one order of magnitude during annealing between 950 and 1150°C, while at the same time also a decrease of the atomic density is observed. We interpret this behavior as a structural relaxation of the amorphous network structure that is governed by annihilation of interstitial-like defects.