The role of ultra-thin carbon barrier layers for fabrication of La/B4C interferential mirrors: Study by time-of-flight secondary ion mass spectrometry and high-resolution transmission electron microscopy

• 375 nm-thick 50 periods La/B4C, La/C/B4C and La/B4C/C X-ray interferential mirrors
• Time-of-flight secondary ion mass spectrometry depth profiling
• 0.5 nm C barrier suppressed the broadening of interface between La and B4C layers
• Chemical interaction and reaction diffusion mechanisms
• The form of depth profiles depends on the interplay of these mechanisms

Time-of-flight secondary ion mass spectrometry and high-resolution transmission electron microscopy study is reported on depth profiling of 375 nm-thick multilayer La/B4C interferential mirrors produced by magnetron sputtering for X-ray radiation at the wavelength of 6.7 nm. The introduction of ultra-thin (0.5 nm) carbon barrier layer inside each period of ca. 7.5 nm suppressed the broadening of interface regions, decreased the width of La and B profiles and as a result improved the reflectance of mirrors. Depending on the layers' sequence (La/C/B4C or La/B4C/C upward the Si substrate), two different mechanisms–chemical interaction and reaction diffusion, were employed for qualitative explanation of the obtained results.