Guiding of low-energy electrons by highly ordered ${\mathrm{Al}}_2{\mathrm{O}}_3$ nanocapillaries

We report an experimental study of guided transmission of low-energy $(200–350\mathrm{eV})$ electrons through highly ordered ${\mathrm{Al}}_2{\mathrm{O}}_3$ nanocapillaries with large aspect ratio ($140\mathrm{nm}$ diameter and $15\mathrm{\mu }\mathrm{m}$ length). The nanochannel array was prepared using self-ordering phenomena during a two-step anodization process of a high-purity aluminum foil. The experimental results clearly show the existence of the guiding effect, as found for highly charged ions. The guiding of the electron beam was observed for tilt angles up to $12°$. As seen for highly charged ions, the guiding efficiency increases with decreasing electron incident energy. The transmission efficiency appeared to be significantly lower than observed for highly charged ions and, moreover, the intensity of transmitted electrons significantly decreases with decreasing impact energy.

Figure 1

(a) Definition of the observation $\left(\theta \right)$ and tilt $\left(\varphi \right)$ angles. (b) The energy loss spectrum of transmitted electrons of $290\mathrm{eV}$ for $\theta =\varphi =0°$.

Figure 2

(Color online) Angular distributions of electrons transmitted through the ${\mathrm{Al}}_2{\mathrm{O}}_3$ nanocapillaries for different tilt angles $\left(\varphi \right)$ and impact electron energies $\left(E_0\right)$.

Figure 3

(Color online) (a) Relative transmission as a function of the tilt angle, for different electron energies $\left(E_0\right)$. Experimental points are fitted by the function (1) (see text). (b) Relative transmission as a function of $E_0$ at zero tilt $\left(\varphi \right)$ and observation $\left(\theta \right)$ angles. (c) Time dependence of the intensity of transmitted electrons at $E_0=250\mathrm{eV}$ and $\varphi =\theta =0°$. The data collection starts at about $30\mathrm{s}$ after the electron beam is turned on, after a discharging time of about $40\min$. The experimental points are fitted by a second-order exponential decay function.