Dependence of field emission properties of carbon nanotube films on their graphitization

Abstract

The purpose of this study is to investigate the effect of graphitization of carbon nanotube (CNT) films on their field emission efficiencies. CNT films were prepared by microwave plasma-enhanced chemical vapor deposition (MPCVD) method. Transmission electron microscopy images reveal the center hollowness and multiwalled structure of a CNT. The tip-growth mechanism of the CNTs prepared by MPCVD is confirmed by the nickel particles enclosed at the tips of the CNTs. The intensity ratio of IG∕(ID+IG) under the Raman spectrum was defined to characterize the degree of graphitization of the CNTs. At any methane flow ratios [CH4∕(H2+CH4)], the CNT graphitization increases with the microwave power. Also, the CNT graphitization increases with the CH4 flow ratio and begins to drop at the flow ratio of 15%. It is mainly attributed to the relative concentration of carbon radicals in the hydrocarbon-based plasma. Enhancement of the graphitization of CNT emitter array leads to the decrease of the threshold field and the increase of the field-controlled current density consistently. This consistency suggests that higher concentration of sp2 bonding enhances conductivity. Therefore, the field emission efficiency of the CNTs increases with the CNT graphitization. At the microwave power of 1200W and the methane flow ratio of 15%, the graphitization intensity ratio is 0.637. The optimal threshold field and field-controlled current density at the field of 3V∕μm are 1.38V∕μm and 8.934mA∕cm2, respectively.

Enhanced Field Electron Emission from Electrospun Co-Loaded Activated Porous Carbon Nanofibers

“…27 Graphitic structure of the carbon exhibits high electrical conductivity, and increasing the degree of graphitization leads to a decrease in the threshold field and an increase in the field-controlled current density and hence an increase in the electrical conductivity. 23 Thus, the amount of the emitted electrons significantly increases with increasing degree of graphitization.…”

“…The observed electron emission enhancement is a consequence of several factors including (i) the creation of greater numbers of conduction pathways for electron movement in the fibers, (ii) dramatic increases in the specific total surface area of the CNFs as a result of producing more porous structures that enable more electrons to be scattered from the surfaces, (iii) formation of a strong electric fields at the formed, sharp, and hard graphitic pore edges that interact with the high energetic electron beam, and (iv) the presence of more Co particles that provide a greater number of conduction pathways in the fibers . Graphitic structure of the carbon exhibits high electrical conductivity, and increasing the degree of graphitization leads to a decrease in the threshold field and an increase in the field-controlled current density and hence an increase in the electrical conductivity . Thus, the amount of the emitted electrons significantly increases with increasing degree of graphitization.…”

“…20−22 In comparison to amorphous or less graphitized carbon, more graphitized carbon, whose generation requires extra high temperature heat treatment processes, emits more electrons. 23 On the other hand, doping carbon with titanium, silicon, chromium, nickel, copper, magnesium, and/or iron initiates results in catalytic graphitization of carbon, and hence, highly graphitic structures can be produced at lower temperatures. 24 Cobalt, another metallic element, has very interesting field electron emission properties and as such can be used as a dopant for carbon to increase field electron emission efficiencies.…”

The development of luminance uniformity measurement for CNT-BLU based on human visual perception

“…First, the quantum mechanical tunneling phenomenon is highly dependent on both the material properties and the shape of the cathode (emitter) [12]. An uneven surface such as a sharp needle shape from the emitter electrode can create convergent equipotential lines that generate a strong local electric field at the surface of the emitter and thus energize bright pixels.…”

The mechanism of the surface morphology transformation for the carbon nanotube thin film irradiated via excimer laser

“…Moreover, the degree of graphitization could be characterized by the intensity ratio of I G /(I D þ I G ), and the higher I G /(I D þ I G ) ratio represented the higher degree of graphitization. 14 The I G /(I D þ I G ) ratio increased from 0.3485 to 0.4613 after excimer laser irradiation. The Raman results implied that the high laser energy irradiation would lead to graphitization of the CNT thin film.…”