Abstract
Vertically aligned carbon nanotube (CNT) arrays show potential for the development of planar low-voltage emission cathodes. The characteristics of cathodes can be improved by modifying their surface, e.g., by hydrogen plasma treatment, as was performed in this work. The surface of multi-walled CNT arrays grown on silicon substrates from toluene and ferrocene using catalytic chemical vapor deposition was treated in a high-pressure (~104 Pa) microwave reactor. The structure, composition, and current-voltage characteristics of the arrays were studied before and after hydrogen plasma treatment at various power values and durations. CNT tips were destroyed and catalytic iron was released from the CNT channels. The etching rate was influenced by iron particles that formed on the array surface. The lower emission threshold in the plasma-treated arrays than in the initial sample is explained by the amplification factor of the local electric field increasing due to graphene structures of unfolded nanotube layers that formed at the CNT tips.
Highlights
Due to the high aspect ratio, mechanical strength, chemical inertness, and high electrical conductivity of carbon nanotubes (CNTs), this material is attractive for electronics, electrochemistry, and for the design of composite materials
A specific feature of the proposed CNT array synthesis is that the reactor is constantly fed with the reaction mixture, namely, a solution of ferrocene in toluene
Since the CNT growth starts from the substrate, the excess iron formed on the substrate as a result of ferrocene decomposition throughout the synthesis is captured inside the channels of the nanotubes being formed [43]
Summary
Due to the high aspect ratio, mechanical strength, chemical inertness, and high electrical conductivity of carbon nanotubes (CNTs), this material is attractive for electronics, electrochemistry, and for the design of composite materials. CNT tips to decrease the macroscopic threshold of electron emission into a vacuum [1,2,3]. This property of CNTs can be used to develop low-voltage-emission cathodes for microwave amplifiers, microfocus. The devices can use both individual nanotubes and CNT arrays that are aligned vertically to the cathode surface. Efficient operation of cathodes composed of vertically-aligned CNTs requires the array surface to be geometrically uniform to provide a constant amplification factor and a constant work function at different parts of the surface
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