Atomic layer epitaxy of TiO_2/ZnO multilayer optics using ZnO buffer layer for 'water-window' x-ray

摘要

A novel TiO_2/ZnO multilayer deposited by atomic layer epitaxy technique has been fabricated to achieve a high reflective mirror and an attosecond chirped mirror in soft-x-ray "water-window" ( X =2.332-4.368 nm) wavelengths region. The technique in this study is able to satisfy reguirements for atomic layer control through epitaxial growth using sequential surface reaction and self-limiting nature. In preliminary experimental studies, both rutile TiO2 (200) and wurtzite ZnO (0001) thin films were grown epitaxially on the same sapphire (0001) substrates at 450°C and moreover a high reflectivity of 29.8% was obtained at around 2.734 nm and a grazing angle of 2 θ =10° .rnThe authors conducted the ALE experiment of TiO_2/ZnO multilayer using a ZnO buffer layer. As a result, the multilayer using a buffer layer was able to be grown epitaxially on not only sapphire (0001) but also Si (100). In addition, reflectivity of multilayer remained to be 24.6% even on Si (100) in contrast with that about 27.5% on sapphire (0001) at grazing angle of 2θ = 8° . Thus, the ZnO buffer layer becomes the key layer to fabricate the TiO_2/ZnO multilayer on various substrates. In the presentation, ALE of TiO_2/ZnO multilayer mirrors using buffer layer will be shown in detail.