Study Of Carbon-Nanotube Field-Emission Cold Cathodes

Carbon nanotubes (CNTs) have excellent performance in field emission. They can be used as field emission cold cathodes. It has brought a promising future in their scientific studies and engineering applications. Fabrication and characterization of carbon-nanotube cold cathodes are studied. The research shows a high field-emission current density (6.5A/cm~2). It indicates that CNTs is a prospective material as field emission cold cathodes which have high field-emission current density. The CNTs cathodes are fabricated by thermal chemical vapor deposition (CVD) and screen-printing method. Their field emission properties are measured using diode structure in an ultra-high vacuum chamber.The CNTs cathodes are fabricated on Ni catalyst coated on different substrates (such as Au film coated on Si substrates, Mo cylinder, Mo flat, Cu flat, stainless steel flat) by thermal chemical vapor deposition (CVD). Different catalyst distributing patterns are also used in the experiment. The surface morphology characteristic of CNTs is examined by SEM. The field emission properties of CNTs are also studied.A recent experimental observation of high field-emission current density (6.5 A/cm~2) from carbon nanotube emitters is presented. Carbon nanotubes are grown on Ni catalyst with thickness of 50, 70, 100 nm coated on Si substrates by chemical vapor deposition. Our research shows that it is beneficial for getting the high current density in our experiment that Au film was deposited onto Si substrate before evaporating a Ni catalyst dot (0.13 mm in diameter) onto the substrate. The field emission characteristics of CNTs cathodes grown on the Ni films with different thickness of 50, 70 nm are compared. The thickness of the Ni film influences the growth of CNTs, which affect the field emission properties. CNTs morphology is changed after the field emission test, which also affect the field emission properties.The CNTs cathodes are also fabricated by screen-printing method. The purification of CNTs, the preparation of CNTs paste, the technique of screen-printing method and the sinter of the sample are studied. The surface morphology characteristic of CNTs is examined by SEM and TEM. A way to fabricate satisfying CNT field emission cathodes by screen printing is found. The CNTs cathodes fabricated by screen-printing method are compared with the CNTs cathodes fabricated by CVD.