The Structural And Optical Property Of Pd/B₄C Multilayer With Large Surface Size For Synchrotron Radiation X-ray Multilayer Monochromator

The X-ray beamline construction and performance upgrade of synchrotron radiation have increasingly higher technical requirements for the required X-ray multilayer monochromator,which has become the key component to its function realization and performance improvement.Due to the high theoretical reflectivity in the7–24 ke V region,Pd/B₄C multilayers with ultrathin layer are the best multilayer material choice for synchrotron radiation X-ray monochromator in this energy range.In order to meet the application requirements of synchrotron radiation X-ray monochromators for large-size and high-quality multilayer devices,the structure of Pd/B₄C multilayer devices were designed,and the key processing parameters such as sputtering gas and sputtering pressure have been studied for fabricating Pd/B₄C multi-layers.The mechanism of key parameters such as sputtering gas and sputtering pressure on the microstructure of Pd/B₄C multilayer was studied,the depositing process was optimized,and the reflectivity of Pd/B₄C multilayers were improved.Linear deposition system based on magnetron sputtering technique has established a method for regulating the deposition rate of films with nano-thickness in large size.For the application in synchrotron radiation X-ray monochromators,the time and temperature stability of Pd/B₄C multilayer devices with large-size have been studied to provide the theoretical guidance for their practical application.Firstly,according to the application requirements of the small-angle scattering line station of SSRF,the structures of Pd/B₄C multilayer devices were designed and the reflectivity could be accurately simulated.Through the study of the dependence of microstructure and interface of Pd/B₄C multilayers on their depositing process,the key parameters such as the sputtering gas pressure and sputtering gas for depositing Pd and B₄C multilayers were optimized for higher reflectivity.The experimental results show that,the lower minimum sputtering pressure and larger interface width were found in these fabricated Pd and B₄C multilayers for Kr than Ar.The Pd/B₄C multilayer made with Kr as the sputtering gas has a better appearance of Pd films,but shows obvious polycrystalline microstructure,low sputtering gas atom content in the film layer,and about 68%reflectivity of the multilayer film to 10 ke V X-rays slightly lower than the Pd/B₄C multilayer film made with Ar as the sputtering gas sample（about 71%）.Secondly,based on the magnetron sputtering coating equipment with the linear motion of the substrate,the film deposition rate distribution law of the circular magnetron sputtering target was experimently studied on the linear motion substrate,and the method of controlling the deposition rate distribution of nano-thickness films was explored by using a mask between the sputtering target and the substrate.The experiment proves that this method has an inhibitory effect on the interface roughness of the multilayer film.The experimental results show that the method based on the mask can reduce the W/Si multilayer film thickness error within 1%.The multilayer film devices for the X-ray monochromator of Shanghai Light Source’s small-angle scattering line station were produced:Pd/B₄C multilayer film devices with dimensions of 150mm×30 mm and 330 mm×30 mm（d=2.5 nm,N=150）,Γ=0.5)film have thickness errors（PV）of 0.27%and 0.75%,respectively;for 10 ke V X-rays,the reflectivity of66.23%and 65.23%,respectively;for 18 ke V X-rays,the reflectivity of 83.00%and80.06%,respectively.Finally,for the application requirements of the small-angle scattering line station of Shanghai Light Source,under offline and online conditions,the time stability and temperature stability of the Pd/B₄C multilayer film were studied.The research results showed that after 20 months under normal temperature dry and atmospheric conditions,the Pd/B₄C multilayer film maintained its reflectivity,roughness and film structure and had not changed;Under the condition of-190℃,the reflectivity of the Pd/B₄C multilayer film decreases by 2-4%,and after returning to room temperature,the reflectivity returns to the initial value.After three temperature shocks,the film structure and reflectivity have not changed;after vacuum annealing at 100℃,The film structure and reflectivity of the Pd/B₄C multilayer did not change significantly.Experimental results show that the fabricated Pd/B₄C multilayer film device has good time and temperature stability,and can meet the long-term use requirements of synchrotron radiation X-ray monochromators.