Properties of Carbon Nanotubes Via a Thin Ti Capping Layer on the Pretreated Catalyst

Abstract

Screening effect and reliability are two of the most important issues in carbon nanotube-based field-emission devices. A thin Ti capping layer has been deposited on the hydrogen-pretreated catalytic iron nanoparticles to control the density of subsequently grown carbon nanotubes. In this way, the screening effect can be remarkably reduced due to the density of carbon nanotubes down to 107 from 109cm−2 as compared to the control specimens. Thus, the turn-on field can be improved to be 2.1 from 3.8V∕μm at the emission current density of 10μA∕cm2 . Furthermore, the electrical breakdown field can be increased to more than 7V∕μm and the lifetime of carbon nanotubes at high electric field (10V∕μm) can be greatly prolonged from a few seconds to more than 1h . This can be attributed to better adhesion and lower contact resistance between the carbon nanotubes and the substrate.

Densification effects of the carbon nanotube pillar array on field-emission properties

“…In general, there are two main mechanisms 27) previously reported for the current decrease. One is the Joule heating effect.…”

Novel ring structure for minimisation of screening effect in carbon nanotube based field emitters

“…Various schemes have been reported for the minimisation of screening effect by growing CNTs bundles with different dot structure and sizes [15,16] rather than growing continuous films of CNTs. Different methods have been reported in the literature for controlling the growth density of CNTs, such as by the capping catalyst particles by deposition of Ti layer [17] and by deposition of buffer layer to enhance the adhesion of CNTs with substrate [18]. Many schemes have been implemented worldwide for the minimisation of shielding effect such as by varying the height and spacing of vertically aligned CNTs [19], controlling the tip densities of CNTs [20].…”

The Reliability Improvements of Carbon Nanotubes Emitters by Utilizing an Fe–Ti Codeposited Catalyst

“…In the first case, it has been reported that the poor adhesion between CNTs and substrates could make the CNTs peel off from the substrates at a high electric field by electric-field-induced force, thereby, causing an abrupt decrease in emission current. [21][22][23] In the second case, Joule heat could be generated in the high resistive regions when a high current density passed through and the residual oxygen in the vacuum chamber tended to attack the defective regions of CNTs. 22,23) This caused a reduction of emission sites and resulted in a gradual degradation in emission current for a long time.…”

“…[21][22][23] In the second case, Joule heat could be generated in the high resistive regions when a high current density passed through and the residual oxygen in the vacuum chamber tended to attack the defective regions of CNTs. 22,23) This caused a reduction of emission sites and resulted in a gradual degradation in emission current for a long time. In an extreme case, ultrahigh current density could even cause CNT evaporation or transfer the CNTs into an amorphous-like material.…”

“…24) Several methods have been proposed to increase the adhesion and/or reduce the contact resistance between CNTs and substrates, such as coating a polymer on CNTs, 25) modifying the interfacial layer between CNTs and substrates, 26,27) making some post-treatment of CNTs, 28) and capping a Ti layer on the hydrogen-pretreated catalytic nanoparticles. 23) However, some of these methods increase the complexity and cost of processing or cause damage to the crystallinity of as-grown CNTs.…”