《X射线衍射与电子显微镜》chap8-薄晶体的电子显微分析-2.pptVIP

析出相与位错 析出相与位错 * * * * 图8-17 与膜面平行的螺位错线使晶柱PQ畸变 可见，晶柱位置确定后（x和y一定），R是z的函数 因为晶柱位于螺位错的应力场之中，晶柱内各点应变量都不相同，因此各点上R矢量的数值均不相同 因为晶体中引入缺陷矢量后，其附加相位角α=2πghkl·R，故 式中，ghkl·b可以等于零，也可以是正、负的整数。 如果ghkl·b =0，则附加相位角就等于零，此时即使有螺位错线存在，也不显示衬度。 如果ghkl·b ≠0 ，则螺位错线附近的衬度和完整晶体部分的衬度不同，其中存在的差别就可以通过下面两个式子的比较清楚地表示出来。 举例：确定fcc晶体中位错的柏氏矢量 （020） （200） （11-1） 位错D、E可见 位错D、E不可见 At reflection (020), g ? b =1, the dislocation is visible; At reflections g1 =(200) and g2 = , g ? b =0, the dislocation is invisible. Thus, b// g1? g2 =[011] take . 确定 b 位错线像总是出现在它的实际位置的一侧或另一侧，说明其衬度本质上是由位错附近的点阵畸变所产生的，叫做“应变场衬度”。 波纹图（Moiré patterns） 波纹图的形成机制 The mechanism of forming moiré patterns is double diffraction. Incident beam K0 produce a diffracted beam K1. If this diffracted beam K1 is very strong, it can be the source of the 2nd diffraction. The K1 enters into the 2nd crystal to produce the 2nd diffraction K2. The moiré pattern is formed by interfering K1 and K2. The total reciprocal vector g=g1+g2. Types of Moiré pattern 平行波纹图（Translational Moiré Fringes） 旋转波纹图（Rotational Moiré Fringes） 混合波纹图（General Moiré Fringes） 平行波纹图 Two crystal planes have different interplanar distances but parallel each other (g1//g2, g1?g2). The interplanar distance of the translational Moiré Fringes is Translational Moiré Fringes The orientation of the translational Moiré fringes is the same as the original pattern but its D value is amplified by with respect to d2 or by with respect to d1. Rotational Moiré Fringes Two crystal planes have the same interplanar distances but different orientations (|g1|= |g2| , rotation angle a is non-zero but very small). ? ?/2 g1 g2 g The interplanar distance of the rotational Moiré Fringes is Rotational Moiré Fringes The orientation of the rotational Moiré fringes is almost perpendicular to the orientation of the original patterns but D value is amplified by 1/a. General Moiré Fringes g1?g2, a