当电子束照射固体试样时，就像是向微观世界发送探测器，会产生多种信号回馈给我们：
I0是入射电子流，单位是A，就像是我们发送的"探测信号"。描述入射电子的另一物理量是电子束流密度，单位是A/cm²，表示信号的集中程度。
IR为背散射电子流，包括两种：
一种是被样品表面原子反射回来的入射电子（弹性背散射电子），它们几乎没有能量损失，就像是从硬墙壁弹回的球。
另一种是入射电子进入固体后通过散射改变方向，最后又从样品表面发射出去的电子（非弹性背散射电子），它们已经损失了部分能量，就像是穿过迷宫后找到出口的探险者。
IS表示二次电子流，由直接击出的原子核外电子和退激发产生的发射电子（如俄歇电子）构成。前者称为（真）二次电子，能量较低；后者称为特征二次电子，能量取分立值。这些就像是被我们的探测信号"惊动"而逃离的原子居民。
IA为样品吸收电流。入射电子在固体中传播时，能量逐渐减小，最后失去全部动能，被样品"吸收"，就像是迷失在迷宫中的探险者。
IT为透射电子流。当样品足够薄时，部分入射电子能够穿过样品，在背面被接收或检测，就像是穿越隧道的光线。
对导电样品（接地），如果忽略透射方向的二次电子发射和表面元素脱附对样品总电荷量的影响，上述电子信号之间满足能量守恒关系：
I0=IR+IS+IA+IT
这些信号就像是微观世界的"密语"，携带着关于固体材料结构、成分、表面状态等性质的丰富信息，通过解读这些信号，我们能够看到肉眼无法直接观察的微观世界。---**Image Extraction:**
**Diagram Description:**
* **Type:** Schematic diagram illustrating the interaction of an incident electron beam with a solid sample and the generation of various signals.
* **Title:** 图2-3 入射电子与固体试样作用产生的信号 (Figure 2-3 Signals generated by the interaction of incident electrons with a solid sample)
* **Main Elements:**
* **Incident Electron Beam:** Represented by a vertical arrow pointing downwards, labeled I₀. It strikes the surface of the sample.
* **Sample:** Represented by a horizontal line indicating the surface and a semi-circular volume below it. An interaction volume is depicted as a dark, tear-drop shaped region starting at the point of incidence and extending into the sample. The volume around this tear-drop shape is also shown.
* **Signals:** Arrows originating from the sample surface or within the sample, representing emitted or generated signals. Each is labeled with a symbol and an associated text description.
* I_S: Arrow pointing upwards from the surface, labeled 二次电子流 (Secondary electron current).
* I_R: Arrow pointing upwards and slightly right from the surface, labeled 背散射电子流 (Backscattered electron current).
* I_X: Arrow pointing upwards and slightly left, originating from within the upper part of the interaction volume. This arrow is associated with the text label 表面元素发射总强度 (Total emission intensity of surface elements). This label is also associated with the symbol I_E via an arrow from I_E pointing to this label. The label most likely refers to characteristic X-rays.
* I_E: An upward arrow originating from the surface/near-surface region, associated with the label 表面元素发射总强度 (Total emission intensity of surface elements). This symbol might represent emitted electrons (like Auger electrons) or be a general label related to surface analysis signals like X-rays. Given the arrow origin and label pointing to I_X, it likely represents X-ray emission from surface elements.
* I_T: Arrows pointing downwards from the bottom of the sample volume, labeled 透射电子流 (Transmitted electron current). These originate from deep within or passing through the sample.
* I_A: Arrow pointing downwards from the sample, connected to ground, labeled 样品吸收电流 (Sample absorption current).
* **Interaction Volume:** Depicted as a dark tear-drop shaped volume where the primary interactions occur. The diagram also shows a larger, lighter volume below the surface. Different signals originate from different depths within these volumes. Secondary electrons originate from near the surface, backscattered electrons from a larger volume closer to the surface, characteristic X-rays from a volume similar to the tear-drop, and transmitted electrons pass through.
* **Electrical Connection:** The sample is shown connected to ground via a wire, with the absorption current I_A flowing into the ground connection.