Organic–inorganic hybrid cathodes: facile synthesis of polypyrrole/zinc oxide nanofibers for low turn-on electron field emitters

Abstract

The identification of new materials capable of sustaining a high electron emission current is a key requirement in the development of the next generation of cold cathode devices and technology. Compatibility with large volume material production methods is a further important practical consideration with solution chemistry-based methods providing for route to industrial scale-up. Here we demonstrate a new class of organic-inorganic hybrid material based on polypyrrole and zinc oxide (PPy/ZnO) nanofibers for use as a low-cost large-area cathode material. Solution chemistry based surfactant chemical oxidation polymerisation is used to synthesise the nanofibers and the macroscopic turn-on electric field for emission has been measured to be as low as 1.8 V/μm, with an emission current density of 1 mA/cm 2 possible for an applied electric field of less than 4 V/μm. Specfic surface area measurements reveal a linear increase in the nanofiber surface area with ZnO incorporation, which when coupled with electron microscopy and x-ray diffraction analysis reveals that the wurtzite ZnO nanoparticles (around 45 nm in size) act as nucleation sites for the growth of PPy nanofibers. Our study demonstrates for the first time how an inorganic nanocrystal acting as a nucleation site allows for the tailored growth of the organic component without diminishing the overall electrical properties and opens the potential of a new type of organic-inorganic hybrid large-area cathode material. The broader impacts and advantages of using hybrid materials, when compared to other composite nanomaterial systems, as large area cathode materials are also discussed.

Surface Structure-Dependent Low Turn-On Electron Field Emission from Polypyrrole/Tin Oxide Hybrid Cathodes

“…Another accentuate trend is the use of intrinsic conjugated polymers for different electronic applications such as solar cells, batteries, supercapacitors, light-emitting diodes, light-dependent resistors, electromagnetic interference shield, and gas sensors because of an easy and economical capability of tuning their morphologies. Polypyrrole (PPy) is one such extensively investigated conjugated polymer with great diversities of surface structures for a wide range of surface-oriented applications. , However, the field-emission properties of these polymers, particularly PPy, are not much explored and have only few reports on pure or hybrid structures of PPy and thus still have lots of potential for the advanced electron emission. − The emission current density from any cathode surface can be determined by three rate-limiting processes described as follows: (i) availability of high concentration of free electrons in the emitting materials or injection of electrons from another source into the emitting material, which may be a back electrode or a substrate such as silicon or any dopant material in the interior of emitter, and the mechanism is the so-called injection-controlled emission process, (ii) transport of free electrons to the emitting surface of the emitter that primarily depends on the conductive islands (such as sp 2 -hybridized grains/clusters in carbon allotropes) or doping states, and the process is known to transport controlled electron emission, and (iii) final emission of electrons through the cathode–vacuum interface, which is defined as the front surface-controlled emission process and is strongly dependent on the surface structure of the emitters, which determines the probability of electron tunneling across the emitter–vacuum interface . Thus, according to Fowler–Nordheim (F–N) hypothesis, the surface structure (i.e., field-enhancement factor) and work function of the cathode emitters are the key parameters for electron-field emitters.…”