B4C/Pd multilayers with small d-spacing can easily degrade in the air, and the exact degradation process is not clear. In this work, we studied the chemical modification of B4C films and B4C/Pd double layers stored in four different environments: a dry nitrogen environment, the atmosphere, a dry oxygen-rich environment, and a wet nitrogen environment. The XANES spectra of the B4C/Pd layers placed in a dry oxygen-rich environment showed the most significant decrease in the σ* states of the B–C bonds and an increase in the π* states of the B–O bonds compared with the other samples. X-ray photoelectron spectroscopy (XPS) measurements of the samples placed in a dry oxygen-rich environment showed more intensive B-O binding signals in the B4C/Pd layers than in the single B4C film. The results of the Fourier-transform infrared spectroscopy (FTIR) showed a similar decrease in the B–C bonds and an increase in the B–O bonds in the B4C/Pd layers in contrast to the single B4C film placed in a dry oxygen-rich environment. We concluded that the combination of palladium catalysis and the high content of oxygen in the environment promoted the oxidization of boron, deteriorated the B4C composition.

Ultrathin Pd/B4C multilayers are suitable X-ray mirrors working at the photon energy region of 7–20 keV. To further improve the layer structure, Pd/B4C multilayers with a d-spacing of 2.5 nm were fabricated by magnetron sputtering using the heavy noble gas Kr and compared with the conventional ones fabricated by Ar. Although the Kr-sputtering process can work at a lower pressure, the interface width—especially the interface roughness—is a little larger than that made by Ar. A stronger polycrystallization and a lower content of sputter gas atoms were found in the Kr-made sample, which can be explained by the joint effect from less recoiled particles and lower sputtering pressure. A good reflectance of 68% of the Kr made multilayer was measured at 10 keV, which is only slightly lower than that of the Ar made sample (71%).

No abstract

No abstract

Pd/B4C multilayers with 2.5 nm of d-spacing and thick Si and B4C capping layers were fabricated to study temporal stability under storage in different environments with relative humidity of 10% and 50%. The two stored samples were investigated using grazing incidence X-ray reflectometry (GIXR), X-ray scattering (XRS), an optical microscope, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The GIXR results showed that the reflectivity of the samples under 10% humidity and 50% humidity dropped by 3% and 8%, respectively, after 13 months. The optical microscope showed that the surface of the 10% humidity sample was smooth and undamaged, whereas the surface of the 50% humidity sample significantly eroded. TEM showed that the internal multilayer structure of the sample stored in 10% humidity was well protected by the capping layers. For the sample stored in 50% humidity, a major part of the Si and B4C capping layers were wrinkled and delaminated, and some surface layers of the multilayer structure were degraded with severe diffusion of boron. The XPS results showed a relatively large amount of oxygen in the B4C capping layer of the 50% humidity sample, and an obvious oxidation of the boron was found in the B4C capping layer and the surface of the multilayer. The severe oxidation and diffusion of boron and the delamination of the capping layers caused the degradation of the Pd/B4C multilayers stored in 50% humidity.