Ultracoherent Single-Electron Emission of Carbon Nanotubes.

Abstract

A single-electron emitter, based on a single quantized energy level, can potentially achieve ultimate temporal and spatial coherence with a large emission current, which is desirable for atomic-resolution electron probes. This is first developed by constructing a nano-object on a metal tip to form a quantized double barrier structure. However, the single-electron-emission current can only achieve a picoampere level due to the low electron tunneling rate of the heterojunction with large barrier width, which limits the practical applications. In this study, carbon nanotubes (CNTs) serve as a single-electron emitter and a current up to 1.5 nA is demonstrated. The double barrier structure formed on the CNT tip enables a high tunneling rate (≈10¹²  s^-1 ) due to the smaller barrier width. The emitter also shows high temporal coherence (energy dispersion of ≈10 meV) and spatial coherence (effective source radius of ≈0.85 nm). This work represents a highly coherent electron source to simplify the electron optics system of atomic-resolution electron microscopy and sub-10 nm electron beam lithography.