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

摘要

We present a new surface structure-dependent cold cathode material capable of sustaining high electron emission current suitable for next-generation low turn-on field-emission devices. The low turn-on electric field for electron emission in the cathode materials is critical, which facilitates the low-power room-temperature operation, a key factor required by the industrial sector. We demonstrate the facile synthesis of polypyrrole (PPy)/tin oxide (SnO2)-based core–shell hybrid cold cathode materials for large area applications. The technique used here is based on a simple and economical method of surfactant-mediated polymerization. The coupled investigation of X-ray diffraction along with electron microscopy reveals the formation of rutile phase SnO2 nanoparticles of size ∼15 nm. These SnO2 nanoparticles act as nucleation sites for the growth of PPy nanofibers, resulting in encapsulated SnO2 nanoparticles in the PPy amorphous matrix. The coupling of spherical-shaped core–shell structures of PPy/SnO2 resulted into the particle train-like nanostructured form of the hybrid material. These core–shell structures formed the local p–n junction between the n-typeSnO2 (core) and p-type PPy (shell). The long chains ofthese p–n junctions in nanofibers result in the modificationof the electronic band structure of PPy, leading to a reduction inthe work function of the electrons. The significant surface structuralmodification in PPy/SnO2 causes a prominent reduction inthe turn-on electric field for electron emission in PPy/SnO2 nanocomposite (∼1.5 V/μm) as compared to the pure PPy(∼3.3 V/μm) without significant loss in current density(∼1 mA/cm²). The mechanism of improved field-emissionbehavior and advantages of using such hybrid nanomaterials as comparedto other composite nanomaterials have also been discussed in detail.