**2.4 Freestanding triboelectric-layer style**

**Figure 1d** shows the moving electrode surface which is a dielectric layer, and the two electrodes were positioned in the similar horizontal direction. The distance between the two symmetric electrodes is lesser than the length of the dielectric layer. The state of the dielectric layer and electrode are the same as in the lateralsliding mode. Once the movement starts, simultaneously, the dielectric layer and bottom electrodes are charged oppositely as mentioned earlier. During movement the dielectric layer is sliding forward and backward, the potential difference is triggered between the two electrodes owing to the change of the affected area, and drives the electron exchanges between them [27, 28].
