光学表面的X射线异常散射现象

X-ray anomalous surface scattering on optical surface

研究了用掠入射散射法测量光学表面散射分布实验中存在的异常散射现象。首先,介绍了实验装置,并用原子力显微镜(AFM)测量了样品的表面粗糙度,给出了工作波长为0.154nm时不同样品在不同掠入射角下的表面散射分布。然后,分析了异常散射角与临界角的关系。最后,对影响散射强度的因素进行了分析。实验结果表明:当掠入射角大于临界角时能观测到光学表面的异常散射现象。在波长一定的情况下,异常散射角与样品材料有关,与掠入射角和表面粗糙度无关;异常散射角略小于临界角,误差变化为-8.6%～-0.9%。另外,镜像反射强度随着入射角和表面粗糙度的增大而迅速减弱,但异常散射强度与镜像反射强度的比值(峰值比)反而随着掠入射角或表面粗糙度的增大而增大,其比值在0.012～2.667变化。结果证明样品的材料和表面形貌是影响异常散射分布的两个重要因素。

An Anomalous Surface Scattering（ASS） phenomenon was researched during the measurement of surface roughnesses for a smooth surface by a grazing X-ray scattering method.Firstly,an experimental facility based on an X-ray diffractometer were introduced.Several kinds of samples with different surface roughnesses were measured by an Atomic Force Microscope（AFM） and their surface scattering distributions in different grazing incident angles were given at working wavelength of 0.154 nm.Then,the relationship between anomalous scattering angles and critical angle was analyzed.Finally,the factors affecting on the scattering intensity were studied.Experimental results indicate that ASS can be observed when the grazing angle is larger than the critical angle.The anomalous scattering angle is related to the sample materials when incidence wavelength is a constant and it changes slightly with the grazing angle and surface roughness（Root Mean Square（RMS））.Moreover,all the measured anomalous scattering angles are slightly smaller than the nominal critical angle values of Si,fused quartz,Ni and Au respectively,and the measurement errors range from-8.6% to-0.9%.On the other hand,the equiangular reflection intensity is reduced obviously as the increasing of the grazing angle and surface roughness,whereas the intensity of ASS radiation is apt to increase instead of being weakened and the ratio of ASS peak intensity to equiangular reflection peak intensity ranges from 0.012 to 2.667.These results prove that sample materials and surface roughness are two principal factors affecting on ASS radiation distribution.