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The self-diffusion of iron and nitrogen is measured in nm range non-magnetic iron nitride thin films. Two non-magnetic iron nitrides, Fe2.23N and FeN, were studied using neutron reflectivity. Neutron reflectivity with a depth resolution in the sub-nm range has a different scattering cross section for isotopes, providing a unique opportunity to measure very small diffusivities. The isotope heterostructure in thin film multilayers [Fe-N/57Fe-N]10 and [Fe-N/Fe-15N]10 were prepared using magnetron sputtering. It was observed that nitrogen diffuses slower than iron although the atomic size of iron is larger than that of nitrogen. It was found that a significantly larger group of N atoms participates in the diffusion process than of Fe, making N diffusion slower than that of Fe. [ABSTRACT FROM AUTHOR]

Self-diffusion was studied in magnetron sputtered nitrogen-rich amorphous compounds of the system Si-C-N by using nitrogen as a model tracer. As shown by infra-red spectroscopy a transient metastable region exists, where the structure of the material can be visualized as silicon nitride tetrahedra which are connected by carbo-diimide (-N=C=N-) bonds to a three dimensional amorphous network. In this region diffusion studies are carried out by neutron reflectometry and isotope multilayers as a function of annealing time, temperature and chemical composition. Low diffusivities between 10-20 and 10-24 m2/s were found. In the metastable region, diffusion is faster than diffusion in amorphous silicon nitride by 1 to 2 orders of magnitude, while the activation enthalpies of diffusion between 3.1 and 3.4 eV are the same within error limits. This can be explained by the fact that the diffusion mechanism along SiN4 tetrahedra is identical to that in amorphous silicon nitride, however, the carbo-diimide bonds seem to widen the structure, allowing faster diffusion. A correlation between diffusivities and the number of carbo-diimid bonds present in the material is found, where the highest diffusivities are observed for materials with the highest number of carbo-diimid bonds, close to the composition Si2CN4. [ABSTRACT FROM AUTHOR]

Abstract: Monochromators used in neutron or X-ray experiments sometimes have unintended higher order contributions. In most cases filters are used to remove them. We sputtered multilayer monochromators with smooth interfaces to reduce the higher order contributions removing the need for a filter. Ni and Ti are selected as sublayer materials due to their high scattering length density contrast. We have strongly reduced the higher order contributions by annealing. This reduces the roughness and off-specular scattering, however the second and third-order Bragg peak intensities increase unexpectedly in neutron reflectivity experiments. [Copyright &y& Elsevier]

Multilayer monochromators can be used in neutron scattering experiments and for synchrotron radiation. Sharp interfaces between the sublayers give higher-order contributions. We created multilayers, consisting of Ni and Ti sublayers, with non-sharp scattering length density profiles at the interfaces to reduce this contributions. The smoothened shape functions have been achieved by introducing intermediate sublayers at the interfaces. The influence of annealing has been investigated with respect to roughness and smoothness of the shape function. Decrease in total reflected intensity for higher-order terms has been observed in reflectivity measurements. [Copyright &y& Elsevier]

Abstract: Thin metallic films produced by sputtering methods show a considerable amount of non-equilibrium point defects, which annihilate during annealing close to room temperature. In order to identify type and migration enthalpy of these defects, volume self-diffusion is studied in ion-beam sputtered nanocrystalline Fe films on short time scales (<20min) and for short diffusion lengths (<2nm) between 250 and 510°C. Neutron reflectometry is applied on [natFe (7nm)/57Fe(3nm)]15 isotope multilayers in order to derive the diffusivities. The diffusivities decrease strongly as a function of annealing time as a result of an annihilation process of non-equilibrium point defects. The initial diffusivities present at the beginning of annealing follow the Arrhenius law with an activation enthalpy of 0.8eV, which is identified as the migration enthalpy of single vacancies by comparison to the literature. The motion of these non-equilibrium vacancies seems to be the dominating mechanism in the annihilation procedure. From the pre-exponential factor an initial vacancy concentration of about 10−12 (mole fraction) can be assessed, which is significantly higher than the corresponding thermal equilibrium value. [Copyright &y& Elsevier]

Self-diffusion experiments based on neutron reflectometry and isotope multilayers in ultrafine-grained copper have been reported. The capability of this method to determine diffusion lengths in the order of 1nm enables the measurement of volume diffusivities in the type B kinetic regime identical to previously published data on single crystals. Such results are difficult to achieve by classical methods of diffusivity determination, such as the radiotracer method, due to limitations of the depth resolution. [Copyright &y& Elsevier]

Abstract: Self-diffusion of the atomic constituents in the solid state is a fundamental transport process that controls various materials properties. With established methods of diffusivity determination it is only possible to measure diffusion processes on a length scale down to 10nm at corresponding diffusivities of 10−23 m2 s−1. However, for complex materials like amorphous or nano-structured solids the given values are often not sufficient for a proper characterization. Consequently, it is necessary to detect diffusion length well below 1nm. Here, we present the method of neutron reflectometry on isotope multilayers. For two model systems, an amorphous semiconductor and an amorphous metallic alloy, the efficiency of this method is demonstrated to detect minimum diffusion lengths of only 0.6–0.7nm. It is further shown that diffusivities can be derived which are more than two orders of magnitude lower than those obtainable with conventional methods. Prospects of this method in order to solve actual kinetic problems in materials science are given. [Copyright &y& Elsevier]

Suezawa et al. [Phys. Rev. B 90, 117201 (2014)] claim in their Comment that the data reported by Shimizu et al. [Phys. Rev. Lett. 98, 095901 (2007)] and Kube et al. [Phys. Rev. B 88, 085206 (2013)] on silicon selfdiffusion for temperatures between 900 and 735 °C are affected by carbon and vacancy clusters and, accordingly, do not reflect self-diffusion under thermal equilibrium conditions. We demonstrate in our Reply that an impact of carbon on self-diffusion can definitely be excluded. In addition it is rather unlikely that the self-diffusion data reported by Shimizu et al. [Phys. Rev. Lett. 98, 095901 (2007)] and Kube et al. [Phys. Rev. B 88.085206 (2013)] are affected by the dissolution of vacancy clusters since strong differences exist not only in the preparation of the samples used for the experiments, but also in the time of diffusion. Finally, the vacancy formation enthalpy deduced by Suezawa et al. [J. Appl. Phys. 110, 083531 (2011)] from quenching experiments is consistent with the value obtained from the temperature dependence of the vacancy formation enthalpy reported by Kube et al. [Phys. Rev. B 88, 085206 (2013)]. Overall we conclude that the quenching experiments of Suezawa et al. [J. Appl. Phys. 110, 083531 (2011)] cannot disprove the interpretation of the low-temperature self-diffusion data reported by Shimizu etal. [Phys. Rev. Lett. 98,095901 (2007)] and Kube et al. [Phys. Rev. B 88, 085206 (2013)]. [ABSTRACT FROM AUTHOR]