Study of film thickness effect on carbon nanotube based field emission devices

Outstanding field emission properties of titanium dioxide /carbon nanotube composite cathodes on 3D nickel foam

Flexible field emission cathodes, as a member of the class of flexible electronic nanodevices, have potential applications in flexible displays and miniature X-ray tubes. In the present review, we first provide an overview of the research progress made in this field, focusing on the fabrication and field emission properties of flexible field emission cathodes based on low-dimensional inorganic semiconductor nanostructures, which are typically grown on flexible substrates, such as polymers, graphene and carbon fabrics. After this, we provide a brief introduction to the major features of flexible field emission cathodes. Subsequently, we shed some light on their potential applications in field emission displays and X-ray tubes. Finally, we discuss future prospects in the further development of flexible field emission cathodes.

Flexible low-dimensional semiconductor field emission cathodes: fabrication, properties and applications

Al-Doped SiC nanowires wrapped by the nanowire network were synthesized by a simple one-step calcination method. The characterization results showed that the nanowire network, which wrapped Al-doped SiC nanowires, was constructed of superficial Al-doped SiC nanowires and SiO2 particles grown on the nanowire intersections. The synergistic effect of Al doping and the unique morphology endowed the as-constructed products with a lower turn-on field of 0.45 V μm−1 and threshold field of 2.8 V μm−1 as well as robust current emission stability. The simulation results from first principles proved that the band gap of SiC was narrowed after Al doping, which was more favorable for electron transmission from the valence band to the conduction band. More importantly, at a high current density of 10 mA cm−2, the emission current fluctuation was less than 2.3% over 600 min. The stability measured at high current density was ascribed to the protection of the superficial nanowire network. This work will provide a new insight into the fabrication of field emission cathode materials with both low turn-on and threshold fields and robust current emission stability at high current density.

Al-Doped SiC nanowires wrapped by the nanowire network: excellent field emission property and robust stability at high current density

A self-powered field emission device (FED) driven by a single-electrode tribo-electric nanogenerator (TENG) is demonstrated. The mechanical motion works as both a power supply to drive the FED and a control unit to regulate the amount of emitted electrons. By using the Fowler-Nordheim equation and Kirchhoff laws, a theoretical model of this self-powered FED is proposed, and accordingly the real-time output characteristics of the device are systematically investigated. It is found that the motion distance of the TENG controls switch-on of the FED and determines the charge amount for emission, while the motion velocity regulates the amplitude of emission current. The minimum contact area for the TENG to generate field emission is about 9 cm2, which can be improved by optimizing FED structure and the tribo-materials of TENG. The demonstrated concept of this self-powered FED as well as the proposed physical analysis can serve as guidance for further applications of FED in such fields of self-powered electronics and soft electronics.

Field emission device driven by self-powered contact-electrification: Simulation and experimental analysis

Utilizing carbon nanotubes (CNTs) as substitutes for the conventional rigid indium–tin oxide (ITO) electrodes, all CNT based flexible field emission devices (FEDs) were possible to prepare with a novel film transfer method. In the method, both CNT-based flexible cathode and anode were fabricated by first attaching the vacuum filtered CNT film/mixed cellulose eater (MCE) filter membrane to an adhesive semi-cured poly(dimethyl siloxane) substrate, and then peeling off the MCE filter membrane. Effects of bending direction and bending radius on field emission properties were studied. The field emission performance of the convex bending device was worse than that of the flat device and deteriorated further with the decrease of bending radius. In contrast, the concave bending device exhibited better field emission properties than the flat device; nevertheless, its field emission properties decreased as the concave bending radius reduced below a certain value. The method achieved two successes. One is that the interfacial interaction between CNT films and the flexible substrate was greatly enhanced. The other is that the transfer process improved the field emission properties due to the increase of vertically aligned CNT tips. Compared with traditional methods applied in FED preparation, the novel modified transfer method is organic free, easy to control, cheap, and environment friendly.

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Peng Xu

Papers

All carbon nanotube based flexible field emission devices prepared through a film transfer method