吸收限附近GaAs在劳厄情况下的荧光溢出

THE FLUORESCENCE EMISSION FROM GaAs IN THE LAUE CASE NEAR THE ABSORPTION EDGE

利用同步辐射光源，在Ｇａ和Ａｓ的Ｋ吸收限之间调节入射Ｘ射线的能量时，在对称劳厄情况下，ＧａＡｓ的（２００）衍射峰附近可观测到从ＧａＡｓ的入射面出射的Ｇａ的Ｋ系荧光Ｘ射线．当入射Ｘ射线的能量改变时，荧光曲线的非对称性会发生变化，变化趋势与相应的对称布喇格情况相类似．但是，劳厄情况下的变化不能解释为晶体内部Ｘ射线驻波的波节面相对于ＧａＡｓ（２００）格子面的移动．在劳厄情况下，Ｘ射线驻波的振幅随入射角的变化与结构因子的相位密切相关，因此结构因子的相位变化也会导致荧光曲线的非对称性变化．在假设原子的荧光溢出与该原子所在位置的电场强度成正比的基础上，给出了计算完整晶体在劳厄情况下荧光溢出的公式．

Abstract The Ga K fluorescence X rays emitted from the incident surface of GaAs perfect crystal were observed around the (200) reflection peak in the Laue case,while tuning the energies of incident X rays from a synchrotron radiation source between the K absorption edges of the Ga and As atoms.With the change of the energies of incident X rays,the asymmetry of the fluorescence X ray curves will change accordingly,the tendency is similar to that in the Bragg case.However,the variation in the Laue case cannot be explained by the moving of the nodal planes of X ray standing wave (XSW) with respect to (200) diffraction plane of GaAs.In the Laue case,the variation of the amplitudes of XSW with the incident angle is closely related to the phase of the structure factor,whose change will result in the change of the asymmetry of fluorescence curves.Under the assumption that the fluorescence yield is proportional to the electric field intensity at the position where the atoms are located,the formulae for calculating the fluorescence emission in the Laue case for perfect crystals are derived.The agreement of the experimental results with the new formulae is quiet good.