Nitridated Pd/B_4C multilayer mirrors for soft X-ray region: internal structure and aging effects

Abstract

Reactive sputtering with a mixture of argon and nitrogen (N₂ partial pressure of 4%, 8%, and 15%) as the working gas is used to develop the high reflectance Pd/B₄C multilayers for soft X-ray region application. Compared to the pure Ar fabricated sample, the interface roughness of the nitridated multilayer is slightly increased while the compressive stress is essentially relaxed from -623 MPa (pure Ar) to -85 MPa (15% N₂). A maximum reflectance of 32% is measured at the wavelength of 9.5 nm for the multilayer fabricated with 15% N₂. After storing the multilayers in an air environment for 6-17 months, a distinct aging effect is observed on the nitridated samples. The transmission electron microscopy results indicate that a large part of the top layers of the nitridated samples is deteriorated with severe interdiffusion, essential decrease in d-spacing, and compacted multilayer structure. The deterioration is less pronounced for the multilayers fabricated with a higher ratio of N₂. Energy dispersive X-ray spectroscopy reveals that the concentration of nitrogen and boron in the degraded area is much reduced compared to the intact layers. A primitive model of upward diffusion of nitrogen and boron is proposed to explain the aging effects of the nitridated structure.

Internal Structure and Temporal Stability of Hard X-ray Pd/B4C Multilayer Mirrors under Different Humidity Environments

“…This could play an important role in the degradation process. The reduced B content in the damaged area was also observed in the nitridated Pd/B4C multilayers after several months of aging [16]. The oxygen content in the damaged area seemed Figure 5.…”

“…The measured d-spacing was around 2.56 nm, which was the same as the GIXR. Figure 5d shows that there was a weak diffraction ring that corresponded to Pd (111) [16,17]. This means that the Pd layers in the multilayer had weak polycrystallization.…”

“…After two years of storage, multilayers with thick Si(O 2 ) caps still produced well-ordered Bragg peaks. Huang et al [16] studied the temporal stability of the nitridated Pd/B 4 C multilayers with relatively large d-spacing of 5 nm and found that the reflectivity of the nitridated Pd/B 4 C multilayers decreased rapidly within a half-year in storage conditions with 20% humidity and at room temperature, which was even worse than the pure Ar-made sample. The sample deposited with a mixture gas of 96% Ar and 4% N 2 degraded faster than the sample deposited with 15% N 2 .…”

Extreme Ultraviolet Multilayer Nanostructures and Their Application to Solar Plasma Observations: A Review

“…120 Furthermore, a considerable reduction of the structure stress can be obtained by adding nitrogen in the atmosphere during the deposition process, although the reflectance loss is higher than 30%. 121 An alternative film characterized by a high theoretical reflectance in the 8-12 nm wavelength range is the Y/Pd stack. 112 Unfortunately, in such structures the severe intermixing occurring between Pd and Y layers results in an almost total disappearance of the interfaces inside the multilayer structures with a dramatic decrease of the reflectance.…”

Comparative Study of Pd/B4C X-ray Multilayer Mirrors Fabricated by Magnetron Sputtering with Kr and Ar Gas

“…Although the Pd/B 4 C multilayer fabricated by Ar showed relatively small interface widths [ 18 ], a significant drop in experimental reflectivity compared to the theoretical value still exists, especially after double reflections as used in the monochromator. The reactive sputtering technique using a mixture of Ar and N 2 gases was tested on Pd/B 4 C multilayer, resulting in a greater interface roughness [ 21 ]. According to our knowledge, the sputtering process using heavier gases than Ar has not been reported on hard X-ray multilayers.…”