In recent years, by using the etching techniques with great precision, the ion tracks in materials were converted into insulator and metal nanocapillaries. The physical and chemical properties of the inner surface on micro and nano-scales of these capillaries can be investigated by the interaction of ions with the surfaces. Stolterfoht et al. (2002 Phys. Rev. Lett. 88133201) have found the evidence for capillary guiding in studying the transmission of 3 keV Ne7+ ions (energy/charge E/q≈100 kV) through the polymer nanocapillaries. The self-organized charge-up process was thought to inhibit close contact between the ions and the inner capillary walls. Skog et al. (2008 Phys. Rev. Lett. 101223202) investigated the guiding effect of 7 keV Ne7+ ions (E/q ≈100 kV) transmitted through SiO2 nanocapillaries, and found the evidence of sequentially formed charge patches along the capillary. For these keV highly charged ions with E/q ≈ 100 kV, the charge patches were formed in a very short time, and then the repulsive electric field rapidly becomes strong enough to deflect the ions, then the ions move along the capillary axis without charge exchange. Zhou et al. (2016 Acta Phys. Sin. 65103401) have investigated the transmission of 100 keV protons (E/q≈102 kV) through the nanocapillaries in polycarbonate (PC) membrane. It was found that the transmitted ions are located around the direction of the incident beam, rather than along the capillary axis. This indicated that the transmission mechanism of hundreds of keV protons through nanocapillaries is significantly different from that for keV highly charged ions. For 100 keV protons, several charge patches suppress the protons to penetrate into the surface, and the protons are transmitted via twice specular scattering near the surface and finally emitted along the incident direction. However, the study of the transmission of E/q≈101 kV ions through nanocapillaries is still lacking. In this work, we measure the time evolution of the relative transmission rate, charge state and angular distribution as well as the full width at half maximum of 20 keV protons (E/q ≈101 kV) transmitted through the nanocapillaries in PC membrane at a tilt angle of+1?. We observe a very long time pre-guiding period before the stable guiding process is established. During the pre-guiding period the direction of the transmitted H+ ions changes to the direction of capillary axis gradually. The transmitted H0 particles are composed of two peaks: the higher and sharper one is nearly in the beam direction, the wider and lower one is around the guiding direction. With the continuous charging-up process, the intensities of the narrow and sharp peak of transmitted H0 near the beam direction will decrease and disappear at the end. The data indicate that the scattering and guiding forces are both important for E/q ≈ 101 kV ions during the period of pre-guiding process, and the guiding force is dominant till a long time pre-guiding period is ended. This finding will fill in the gap between E/q ≈100 kV and 102 kV of previous studies of ions transmitted through nanocapillaries. It is also helpful for finding the applications of nano- and micro-sized ion beams produced by tapered glass capillary with E/q ≈101 kV.%测量了20 keV质子穿过倾斜角为+1?的聚碳酸酯微孔膜后,出射粒子的位置分布、相对穿透率以及电荷纯度随时间的演化.实验发现,能量电荷比E/q≈101 kV的质子穿过绝缘纳米微孔的物理机理与E/q≈100 kV和E/q≈102 kV区域离子有显著不同.对于E/q≈101 kV的质子穿过绝缘纳米微孔,存在一段相当长的导向建立之前(导向前)的过程,在该时期内出射质子及氢原子的特性和导向建立后的特性有很大差异.在导向前的演化过程中,我们可以观察到出射质子的峰位逐渐向孔轴向附近转移;出射氢原子由束流方向的尖峰以及孔轴向的主峰构成,峰位角保持基本不变且尖峰逐渐消失.这一过程的主要机理为微孔内表面以下的多次随机二体碰撞和近表面镜面反射两种传输方式逐步向电荷斑约束下的"导向效应"过渡的过程.对E/q≈101 kV区间离子"导向前过程"的完整观测,使得对低能向中能过渡区间离子穿过绝缘微孔膜物理机制和图像有更深入和完整的认识,有助于约10 keV离子微束的精确控制和应用.
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