The structural characterization of heat-treated CN films fabricated by dual-facing-target sputtering for soft X-ray multilayer mirrors was performed by means of X-ray diffraction (XRD), Raman spectroscopy (RS) and X-ray photoelectron spectroscopy (XPS). The XRD analyses indicate a graphization process in the CN films during thermal annealing. The Raman analyses imply that the primary bonding in the CN films is sp2. In other words, the formation of the sp3 bonding in the CN films can be suppressed effectively by doping with N atoms, and thus the thickness expansion resulting from the changes in the density of CN films during annealing can be decreased considerably. This result is also clarified by the increased conductivity measured. The XPS results give the information of the existence of the strong covalent bonding between N and C atoms, which can slow down the tendency of the structural relaxation during annealing. These results suggest that CN films suitable for soft X-ray multilayers used at high-temperature environments can be obtained by reactive dual-facing-target sputtering. With the X-ray diffraction measurements, we do observe the enhanced thermal stability of CoN/CN multilayers.

Thermal stability of Co/C multilayers prepared by a dual-facing-target sputtering system was studied. A picture of the thermally induced changes in the microstructure was obtained using complementary measurement techniques including low-angle and high-angle X ray diffraction, transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. It was found that the period expansion, reflectivity change and compound formation that were observed after annealing are caused by structural changes both in the sublayers and at the interfaces. Below 400℃, the period expansion is mainly caused by the graphitization of the amorphous carbon layers, and a significant increase in the reflectivity at grazing incidence was observed. By 500℃, the crystallization and agglomeration of Co layers induce an enormous period expansion and a serious decrease in reflectivity. A small amount of carbide is found to form at this temperature. Our results imply that new multilayer structures, e.g., compound multilayers will have to be developed for use at high temperatures or under high X-ray incident flux.

We studied the structure and magnetic properties of as-deposited and subsequent annealed CoxC100-x granular films fabricated by a DC facing-target magnetron sputtering system at room temperature using atomic force microscopy, X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy and vibrating sample magnetometer. The average roughness, Ra, of the as-deposited CoxC100-x granular films is smaller than that of Si (100) substrates. X-ray diffraction and transmission electron microscopy analyses indicate that the as-deposited CoxC100-x granular films are composed of～2 nm amorphous cobalt grains dispersed in amorphous carbon matrix, and their morphology is composition independent. The high resolution TEM image of the as-deposited Co30C70 film shows that cobalt and carbon have already separated during the deposition, even if the aggregation of cobalt is not complete. Annealing at 300-450℃ causes the crystallization of amorphous cobalt followed by an increase of grain size and the graphitisation of the amorphous carbon matrix. The constrictions arising from the structural environment result in the coexistence of the hcp and fcc Co phases at temperatures higher than the phase transformation point of 425℃. Magnetic measurements reveal that the coercivity of the as-deposited CoxC100-x granular films decreases with the increasing cobalt composition, and increases with the decrease in film thickness. The enhanced coercivity can be attributed to the weakened intergrain interaction due to the increased percolation threshold and/or the destruction of long-range domain structures caused by the film thickness reduction.

The thermal stability of Co/C soft x-ray multilayers is improved by 100-200 centigrade degrees through doping with N. The low-angle x-ray diffraction of CoN/CN soft x-ray multilayers indicates that their period expansion is only 4% at 400℃, and the interface pattern of the multilayers still exists even if they are annealed at 700℃. High-angle x-ray diffraction and transmission electron microscopy analyses reveal that this crystalline process is significantly retarded by doping with N atoms, leading to a smaller grain size at higher annealing temperatures. Raman spectroscopy analyses of the multilayers give evidence that the formation of the sp3 bonding is suppressed effectively by doping with N atoms, and thus the period expansion is decreased considerably. The strong covalent bonding between N atoms and the ionic bonding between Co and N atoms can slow down the structural relaxation. The significant suppression of grain growth is believed to be attributable to the coexistence of hcp and fee Co structures at annealing temperatures higher than 500℃.

low 400℃, the upward shift of D and G Lines in Raman spectra indicates that the amorphous carbon layers are changing from ones with bond-angle disorder and fourfold-bonding only to ones containing threefold-bonding. In the crystalline stage, the amorphous carbon layers in the as-deposited multilayers crystallize to graphite crystallites in the annealing temperature range of 500-600℃. The rapid increase in the intensity ratio of D line to G line and dramatic decrease in linewidth further confirm this substantial structural change. In the grain growth stage, the specimens are annealed at temperatures higher than 700℃. The decrease in the intensity ratio implies a growth in the graphite crystallite dimensions, which is consistent with the XRD and TEM results.