Micro-focus electron source based on high current density carbon nanotube emitters

A high current density micro-focus cathode based on carbon nanotube (CNT) field emission was developed. The CNT film was grown directly on the nickel alloy substrate with a diameter of $\mathbf{70}\ \boldsymbol{\mu} \mathbf{m}$ by chemical vapor deposition. The effect of the cathode-grid spacing on the field emission properties was investigated, and improved field emission performances were demonstrated for the 1.4 mm spacing with a lower threshold field of $\mathbf{1.6}\ \mathbf{V}/\boldsymbol{\mu} \mathbf{m}$ and higher emission current (up to 19 A/cm²) comparing with spacing of 0.4 mm, indicating that increasing the electrode spacing could enhance the field emission characteristics of the CNT cathode. The X-ray tube based on the CNT micro-focus electron source reached the imaging resolution of about $\mathbf{80}\ \boldsymbol{\mu} \mathbf{m}$.