The electron field emission performance of screen-printed graphene cathode was studied. High-yield graphene was prepared by a modified Hummers method and hydrazine hydrate reduction process, and screen printing technology was used to prepare the graphene field emission cathode. This cathode structure satisfies the requirements of both good electrical conductivity and a high surface field enhancement factor, leading to excellent and stable field emission properties with a low threshold field (~1.5 V µm−1). Our work introduced a simple and convenient method suitable for large scale on different substrates, paving the way for more applications of graphene films.

Electron field emission from screen-printed graphene films.

We report a versatile synthetic process based on rapid heating and cooling chemical vapor deposition for the growth of carbon nanotube (CNT)–graphene hybrid materials where the thickness of graphene and density of CNTs are properly controlled. Graphene films are demonstrated as an efficient barrier layer for preventing poisoning of iron nanoparticles, which catalyze the growth of CNTs on copper substrates. Based on this method, the opto-electronic and field emission properties of graphene integrated with CNTs can be remarkably tailored. A graphene film exhibits a sheet resistance of 2.15 kΩ sq−1 with a transmittance of 85.6% (at 550 nm), while a CNT–graphene hybrid film shows an improved sheet resistance of 420 Ω sq−1 with an optical transmittance of 72.9%. Moreover, CNT–graphene films are demonstrated as effective electron field emitters with low turn-on and threshold electric fields of 2.9 and 3.3 V μm−1, respectively. The development of CNT–graphene films with a wide range of tunable properties presented in this study shows promising applications in flexible opto-electronic, energy, and sensor devices.

Controlled growth of carbon nanotube-graphene hybrid materials for flexible and transparent conductors and electron field emitters.

We report a versatile method based on low vacuum annealing of cellulose acetate on nickel (Ni) surface for rapid fabrication of graphene and carbon nanotube (CNT)–graphene hybrid films with tunable properties. Uniform films mainly composed of tri-layer graphene can be achieved via a surface precipitation of dissociated carbon at 800 °C for 30 seconds under vacuum conditions of ∼0.6 Pa. The surface precipitation process is further found to be efficient for joining the precipitated graphene with pre-coated CNTs on the Ni surface, consequently, generating the hybrid films. As expected, the hybrid films exhibit substantial opto-electrical and field electron emission properties superior to their individual counterparts. The finding suggests a promising route to hybridize the graphene with diverse nanomaterials for constructing novel hybrid materials with improved performances.

Low vacuum annealing of cellulose acetate on nickel towards transparent conductive CNT-graphene hybrid films.

The effect of atmospheric pressure plasma treatment on the field emission characteristics of screen printed carbon nanotubes

While it is well-known that the plasmaenhanced catalytic chemical vapor deposition (PECVD) of carbon nanotubes (CNTs) offers a number of advantages over thermal CVD, the influence of the various individual contributing factors is not well understood. Especially the role of ions is unclear, since ions in plasmas are generally associated with sputtering rather than with growing a material. Even so, various studies have demonstrated the beneficial effects of ion bombardment during the growth of CNTs. This review looks at the role of the ions in plasmaenhanced CNT growth as deduced from both experimental and simulation studies. Specific attention is paid to the beneficial effects of ion bombardment. Based on the available literature, it can be concluded that ions can be either beneficial or detrimental for carbon nanotube growth, depending on the exact conditions and the control over the growth process.

The role of ions in plasma catalytic carbon nanotube growth: A review

Multiwall carbon nanotubes (MW-CNT) have been synthesized from solid-phase graphite. The graphite is deposited as a thick-film paste and irradiated with a 1.2keV flood Ar-ion beam, transforming the graphite surface to a composite of MW-CNT embedded in the graphite matrix. Micro-Raman measurements have verified that the nanotubes are metallic in nature. The technique was used to make printed field-emission cathodes. Emission from these cathodes demonstrates Fowler–Nordheim tunneling characteristics. The irradiated film emits at an extraction field of 5.0V∕μm, which is less than one-sixth of the minimum extraction field of the nonirradiated graphite film, and exhibit lower noise and greater emission uniformity.

Carbon nanotube growth for field-emission cathodes from graphite paste using Ar-ion bombardment

Samples of reticulated vitreous carbon (RVC) and paste graphite film have been evaluated for field-emission properties both before and after surface modification. The RVC has been treated using an open-air laser method. The graphite has been treated using an Ar-ion flood bombardment method. Both methods result in a change in surface morphology of the emission cathode which physically resembles results obtained using current or voltage stress treatment methods. Emission properties become more uniform, exhibit less noise, and, in the best cases, match results seen from carbon nanotubes or ultra-nanocrystalline diamond cathodes. The results demonstrate a method for obtaining large total currents at optimal extraction voltages, from large-area, low-cost cathodes. This method is useful for applications, such as field-emission lamps and x-ray tubes, which do not require nanofabricated, lithographically-patterned cathode structures.

Ion-beam morphological conditioning of carbon field emission cathode surfaces

We present here an X-ray detector based on Si field-emission tip technology. The X-ray is first converted to EHPs in the substrate Si The electrons are emitted into vacuum from spatially-distinct nanoscale field emission tips fabricated on the back-side of the conversion layer, and detected using an imaging multi-channel plate (MCP).

http://ieeexplore.ieee.org/iel5/10773/33938/01619480.pdf

X-ray imaging detector silicon field emission tip array energy conversion

Square-cm samples of bulk graphite, reticulated vitreous carbon, and paste graphite film have been evaluated for field-emission properties both before and after surface modification using a novel Ar-ion flood bombardment method. The Ar-ion treatment results in a change in surface morphology of the emission cathode which physically resembles results of emission treatments using lasers or other heat sources, as well as results obtained using current or voltage stress treatment methods. Emission properties become more uniform, exhibit less noise, and, in the best cases, match results seen from carbon nanotubes or ultra-nanocrystalline diamond cathodes. The results demonstrate a method for obtaining large total currents at optimal extraction voltages, from large-area, low-cost cathodes. This method is useful for applications, such as field-emission lamps and x-ray tubes, which do not require nanofabricated cathode structures.

Yu Wang

Papers

Carbon nanotube growth for field-emission cathodes from graphite paste using Ar-ion bombardment

Ion-beam morphological conditioning of carbon field emission cathode surfaces

X-ray imaging detector silicon field emission tip array energy conversion

Ion-beam morphological conditioning of carbon field emission cathode surfaces