The fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.

We have characterized the previously undescribed parameters for engineering the electrical properties of single-walled carbon nanotube (SWCNT) films for technological applications. First, the interfacial tension between bare SWCNT network films and a top coating passivation material was shown to dictate the variability of the films' sheet resistance (R(s)) after application of the top coating. Second, the electrical stability of the coated SWCNT films was affected by the mismatch between the CTE of the supporting substrate and the SWCNT network film. An upshift in the Raman G-band spectrum of SWCNTs on bare PET suggested that compressive strain was induced by the CTE mismatch after heating and cooling. These findings provide important guidelines for the choice of substrate and passivation coating materials that promote environmental stability in SWCNT-based transparent conductive films.

Flexible field-emission devices (FEDs) based on reduced graphene oxide (RGO) emitters are fabricated by the thermal welding of RGO thin films onto a polymeric substrate. The RGO edges are vertically aligned relative to the substrate as a result of cohesive failure in the RGO layer after thermal welding. Even at large bending angles, excellent electron emission properties, such as low turn-on and threshold fields, a high emission current density, a high field enhancement factor, and long-term stability of the emission properties of RGO emitters, arise from the uniform distribution and high density of the extremely sharp RGO edges, as well as the high interfacial strength between the RGO emitters and the substrate. Al- and Au-doped RGO emitters are fabricated by introducing a dopant solution to the RGO emitters, and the resulting field-emission characteristics are discussed. The proposed approach is straightforward and enables the practical use of high-performance RGO flexible FEDs.

Arrays of tubular-structured reduced graphene oxide (RGO) were fabricated by a simple method involving filtration of a solution containing highly dispersed RGO sheets. The length and alignment of the tubular-structured RGO arrays were controlled by the filtration rate and by tuning the interactions between the hydrophobic RGO sheets and the porous walls, rather than the top surfaces, of the polycarbonate filter membrane. As expected, the lengths of the RGO arrays increased with higher filtration rates; however, maximum field emission characteristics were obtained at an intermediate filtration rate because field screening reduced electron emission from the longer-length RGO arrays. ZnO-coated RGO arrays showed excellent emission stability without significant current degradation or fluctuations, even under O 2 exposure. The ZnO layer protected the emission site of the RGO arrays from the reactive ion bombardment of oxidative gas species. Moreover, the RGO arrays were highly flexible with preservation of the field emission properties, even at large bending angles. The excellent field emission characteristics of the tubular structured RGO arrays were attributed to the high crystallinity, abundant sharp edges, and the chemical stability of the RGO arrays, as well as the strong interactions between the RGO arrays and the substrate.

We present a simple process for the fabrication of high performance transparent conducting films that contain single-walled carbon nanotubes (SWCNTs) noncovalently coated with an ultrathin titania layer. The hydrophobic interactions between nanotube surfaces and the acetylacetone (acac) ligands used to stabilize the TiO 2 precursor provide an interesting alternative method for noncovalently coating the SWCNTs with a titania layer. The ultrathin titania layer on SWCNTs prevented the oxidation of functionalized SWCNTs at high temperatures, and protected against water molecule absorption. Moreover, the uniform and thin titania layer, formed via hydrophobic interactions, promoted the selective removal of amorphous carbonaceous materials upon heating to 300 C as well as withdrawing electrons from the nanotubes. The noncovalent titania coating of the SWCNTs may potentially exhibit other interesting physical properties relevant to applications such as transparent conducting films, photo-catalysis, and sensor electrodes.

Patterned reduced graphene oxide (rGO) films with vertically aligned tip structures are fabricated by a straightforward self-assembly method. The size, uniformity of the patterns, and alignment of the tips are successfully controlled according to the concentration of a GO/octadecylamine (ODA)-dispersed solution. The surface energy difference between the GO/ODA solution and a self-assembled water droplet is a critical parameter for determining the pattern structure. Numerous rGO nanosheets are formed so as to be vertically aligned with respect to the substrate during film fabrication at GO concentrations below 2.0 g/L. These samples provide high field-emission characteristics. The patterned rGO arrays are highly flexible with preservation of the field emission properties, even at large bending angles. This is attributed to the high crystallinity, emitter density, and good chemical stability of the rGO arrays, as well as the strong interactions between the rGO arrays and the substrate.

We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/ TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.