低能电子穿越绝缘体微孔膜动力学过程研究

Dynamic process of low energy electrons through insulating nanocapillaries

采用二维位置灵敏的微通道板探测器对能量为1500 eV的低能电子束穿过孔径为400 nm、未经照射过的的聚对苯二甲酸乙二醇酯(PET)微孔膜后的全角分布以及时间演化进行了测量,同时采用自制的积分式能谱测量装置测量了穿透电子的能量分布。实验结果表明:在充电阶段,当入射电子束束流较弱时,透射电子强度随充电时间逐渐上升;充电过程中,透射电子的角分布宽度由小变大,但是角分布中心基本不随膜的倾角移动。对出射电子达到平衡态时的电子能谱的测量表明,穿透电子的能量保持着入射时的能量。对于理解电子在绝缘体微孔中的传输给出了新的实验证据,给出了可能形成“导向效应”的微孔内部电场的条件。

In the study of the transportation of low energy electrons through insulating capillaries, the experimental results are very different and depending on many conditions. This leads to some controversies on whether the mechanisms of the electron guiding exists or not. This work studies the electron beam with an energy of 1500 eV transmitting through the insulating PET capillaries of 400 nm in diameter. The capillaries have never been irradiated by any beams before. The two-dimensional angular distributions of transmitted electrons and their evolution are measured by a Mirco-channel Plate(MCP) detector with the phosphor screen. The energy distribution of the transmitted electrons is also measured by a mesh system before the MCP detector where the stepping voltages are put on and the transmitted electrons are recorded by the MCP detector accordingly. The experimental results show that the intensity of transmitted electrons increases with the charging time when the capillaries starts to be exposed to the electron beam, and a typical charging-up is observed. During the charging process, the angular distribution width of transmitted electrons increases from small to large, but the center of the angular distribution remains the same. The energy spectrum of the transmitted electrons when they reach the stationary state shows that the most transmitted electrons keep their initial energy. This work provides new experimental evidence for understanding electron transport in insulator micropores, and gives the conditions for the formation of guiding electric field in micropores that may form guiding effect.