扫描电镜材料检测方法[精选].pptVIP

加速电压对 SEM 像的影响  When theoretically considering the electron probe diameter alone, the higher the accelerating voltage, the smaller is the electron probe. However, there are some unnegligible demerits in increasing the accelerating voltage. They are mainly as follows: 1) Lack of detailed structures of specimen surfaces. 2) Remarkable edge effect. 3) Higher possibility of charge-up. 4) Higher possibility of specimen damage. In SEM, finer surface structure images can generally be obtained with lower accelerating voltages. At higher accelerating voltages, the beam penetration and diffusion area become larger, resulting in unnecessary signals (e.g., backscattered electrons) being generated from within the specimen. And these signals reduce the image contrast and veils fine surface structures. It is especially desirable to use low accelerating voltage for observation of low-concentration substances. Always consider Interaction Volume 扫描电子显微术：例子 The effect of Accelerating Voltage on SEM Images Specimen: Toner 墨粉 When high accelerating voltage is used as at (a), it is hard to obtain the contrast of the specimen surface structure. Besides, the specimen surface is easily charged up. The surface microstructures are easily seen at (b). Specimen: Evaporated Au particles. The image sharpness and resolution are better at the higher accelerating voltage, 25 kV. Specimen: Filter paper. At 5 kV, the microstructures of the specimen surface are clearly seen as the penetration and diffusion area of incident electrons is shallow. Fig. 6 Specimen: Sintered powder. At low accelerating voltage, while surface microstructures can be observed, it is difficult to obtain sharp micrographs at high magnifications. Specimen: Paint coat. When a high accelerating voltage is used, more scattered electrons are produced from the constituent substances within the specimen. This not only eliminates the contrast of surface microstructures, but produces a different contrast due to backscattered electron