Design,Fabrication And Properties Of X-Ray Multilayer Mirrors

X-ray is a kind of electromagnetic radiation with wavelength range from 0.01nm to 10 nm.It has been widely concerned and applied in many fields,such as material science field of substance structure detection and characterization,life medical field of medical imaging diagnosis and natural resources,etc.X-ray multilayer mirrors are one of the key components of X-ray instruments,and the preparation of X-ray multilayer mirrors with excellent optical properties is of great significance for improving the performance of X-ray instruments.In the reported X-ray multilayer mirrors,the preparation methods mainly include magnetron sputtering and atomic layer deposition,etc,the magnetron sputtering has the advantages of multiple choice of membrane material,but it has some technical difficulties,such as serious interlayer diffusion,small preparation area,uneven film layer and difficult to control the coating rate.At the same time,the periodic multilayer mirrors with equal thickness can cause color difference and produce X-ray beam with different wavelengthλ,which can’t meet the scientific research needs of X-ray diffraction.X-ray multilayer mirrors with high reflectance,large grazing incidence angle,small roughness,well monochromated and stable film are becoming a research hotspot.In this paper,the reflectance of X-ray multilayer mirrors is simulated and calculated,and two secondary cylindrical multilayer mirrors are designed.Finally,the designed multilayer mirrors are verified experimentally,the specific work is as follows:（1）The reflectance simulation of X-ray multilayer mirrors.In this paper,the reflectance of the multilayer film under ideal interface and rough interface is calculated by Matlab programming.By using the equivalent interface method,the relationship between number of periods N,periodic thickness D,ratio T,grazing incidence angleθand reflectance R of the multilayer mirrors was simulated and calculated respectively.Considering that number of periods N,periodic thickness D,ratio T and grazing incidence angleθof multilayer film have little influence on each other,then,the parameters of the X-ray multilayer mirrors in the condition of the highest reflectance R were determined:number of periods N,periodic thickness D,ratio T and grazing incidence angleθ.Real-Structure model is used to define the relationship between the increase of the roughness with the increase of the thickness,the relationship between the number of periods N,periodic thickness D,ratio T,grazing incidence angleθand reflectance R is simulated and calculated under different substrate roughnessσ₀.The effect of roughness on the reflectance of the multilayer film is further determined accurately.According to the reflectance simulation results,when the multilayer film roughness is greater than 0.5 nm,the reflectance of the multilayer film drops to less than 30%of the ideal reflectance,and the reflectance is low.Therefore,when preparing the X-ray multilayer mirrors,the substrate roughness and the surface roughness of the multilayer mirrors must be below 0.5 nm.（2）Design of quadratic cylinder HfO₂/Al₂O₃gradient multilayer X-ray mirrors.The basic principles and structural parameters of parabolic cylindrical gradient multilayer mirrors and elliptic cylindrical gradient multilayer mirrors are designed and introduced in this paper.The substrate parameters and multilayer parameters of the HfO₂/Al₂O₃parabolic cylindrical gradient multilayer mirrors are designed,which can collimate from X-ray parabola focus point injection,after collimating light beam,both parallel and has a single wavelength,as monochromatic parallel light,one of the parabolic parabolic equation for the focal length of 2p is 0.1646 mm,and the multilayer periodic thicknesses are 3.5 nm and 4.4 nm of M₁and M₂at the two end points of the mirror.The base parameters and multilayer parameters of the HfO₂/Al₂O₃elliptic cylindrical gradient multilayer mirrors are designed,which can focus the X-ray emitted from the focal point of the ellipse,and the focused beam can form light spots at another focal point.The parameters a=210.0230 mm,b=3.1048mm and c=210 mm of the constant elliptic equation of the elliptic cylinder,and the periodic thickness D of the multilayer mirrors at the left end point M₁,the middle point M₂and the right end point M₃on the mirror are 2.73 nm,4.73 nm and 5.46 nm,respectively.（3）HfO₂/Al₂O₃planar multilayer mirrors were prepared by atomic layer deposition（ALD）.In this paper,a variety of HfO₂/Al₂O₃planar multilayer mirrors with different periodic thicknesses were prepared by atomic layer deposition method,and X-ray reflectance tests were conducted on them.One of the HfO₂/Al₂O₃planar multilayer mirrors with periodic thickness D=3.9 nm deposited on Si substrate was more than 10%.First,the deposition rates of HfO₂and Al₂O₃layers were obtained by preparing HfO₂and Al₂O₃layers respectively.The deposition rate of HfO₂layer was1.2（?）/cycle,and that of Al₂O₃layer was 0.96（?）/cycle.Second,by continuously preparing HfO₂/Al₂O₃multilayer with periodic thicknesses of 10 nm,8 nm,6 nm,4nm,3 nm and 2 nm,it is concluded that the ALD equipment used in the experiment can prepare HfO₂/Al₂O₃multilayer with periodic thicknesses of less than 2 nm.Third,in the preparation process of HfO₂/Al₂O₃multilayer mirrors with periodic thickness D=2 nm,the paper improved the deposition technology,and the reflectance of the prepared HfO₂/Al₂O₃multilayer mirrors with D=1.78 nm was close to 1%.Fourthly,HfO₂/Al₂O₃multilayer mirrors with periodic thickness D=3.9 nm were prepared on Si substrate and stainless steel substrate.The reflectance of HfO₂/Al₂O₃multilayer mirrors on Si substrate is more than 10%,showing high reflectance.