The microstructure evolution of magnetron-sputtered Ni/C multilayers was investigated by varying the Ni and C layer thickness in the region of a few nanometers. For the samples having 2.6-nm-thick C layers, the interface width increases from 0.37 to 0.81 nm as the Ni layer thickness decreases from 4.3 to 1.3 nm. Especially for the samples with Ni layers less than 2.0 nm, the interface width changes significantly due to the discontinuously distributed Ni crystallites. For the samples having 2.8-nm-thick Ni layers, the interface width increases from 0.37 to 0.59 nm when the C layer thickness decreases from 4.3 to 0.7 nm. The evolution of interface microstructures with varied Ni and C layers is explained based on a proposed simple growth model of Ni and C layers.

Short-period (~3.5 nm) Co/C multilayer mirrors are fabricated by the direct current magnetron sputtering technique through the addition of a small proportion of nitrogen (4-15% partial pressure) to the working gas (Ar). The addition of nitrogen has been demonstrated to significantly suppress the interdiffusion of neighboring materials due to the nitridation of carbon layers as compared with the Co/C multilayer fabricated with the use of pure Ar. The optimal partial pressure of nitrogen was found to be 6%. At this pressure, nitrogen provides abrupt interfaces and the maximal peak value (19%) of the s-polarized radiation reflectivity at the 251-eV photon energy and 45° angle of incidence. The p-polarized radiation reflectivity proved to be less than 0.3%, demonstrating high potentialities of the nitridated Co/C multilayers as Bragg polarizers in the 4.5-6.5-nm spectral range.

We have coupled a nano-focused synchrotron beam into a planar x-ray waveguide structure through a thinned cladding, using the resonant beam coupling (RBC) geometry, which is well established for coupling of macroscopic x-ray beams into x-ray waveguides. By reducing the beam size and using specially designed waveguide structures with multiple guiding layers, we can observe two reflected beams of similar amplitudes upon resonant mode excitation. At the same time, the second reflected beam is shifted along the surface by several millimeters, constituting a exceptionally large Goos-Hänchen effect. We evidence this effect based on its characteristic far-field patterns resulting from interference of the multiple reflected beams. The experimental results are in perfect agreement with finite-difference simulations.

Iterative phase retrieval has been used to reconstruct the near-field distribution behind tailored X-ray waveguide arrays, by inversion of the measured far-field pattern recorded under fully coherent conditions. It is thereby shown that multi-waveguide interference can be exploited to control the near-field distribution behind the waveguide exit. This can, for example, serve to create a secondary quasi-focal spot outside the waveguide structure. For this proof of concept, an array of seven planar Ni/C waveguides are used, with precisely varied guiding layer thickness and cladding layer thickness, as fabricated by high-precision magnetron sputtering systems. The controlled thickness variations in the range of 0.2 nm results in a desired phase shift of the different waveguide beams. Two kinds of samples, a one-dimensional waveguide array and periodic waveguide multilayers, were fabricated, each consisting of seven C layers as guiding layers and eight Ni layers as cladding layers. These are shown to yield distinctly different near-field patterns.

Magnetron-sputtered Ni/C multilayers with a periodic thickness below 4 nm are difficult to produce, and reactive sputtering with nitrogen is a feasible method. The effects of nitrogen on the reflectivities of Ni/C multilayers were investigated. Pure argon and three mixing ratios of 4%, 8%, and 15% nitrogen-argon gas mixture were used as the working gas. For all Ni/C multilayer samples, each contains 40 bilayers. The nominal structure has a periodic thickness of 3.8 nm, with a ratio of the thickness of the Ni layer to the periodic thickness of Г = 0.39. The results of grazing incidence X-ray reflectivity (GIXRR) measurements indicate that reactively-sputtered Ni/C multilayers have a lower interface width and higher specular reflectance. It was shown in transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) measurements that a periodic layered structure can still be clearly observed in Ni/C multilayers with pure argon, but with quite rough interfaces between the adjacent layers. For Ni/C multilayers with the mixing ratio of 4% nitrogen-argon gas mixture, it is found that the interfaces between Ni and C layers become smoother and sharper. Additionally, nitrogen incorporation can reduce the mobility of Ni atoms, which decreases the threshold thickness that Ni layers would become continuous. This may be also a reason which accounts for the better interface quality of reactively-sputtered Ni/C multilayers. Meanwhile, Ni/C multilayers deposited with a nitrogen-argon gas mixture have lower stress due to the reduction in Ni adatom mobility.