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

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-type SnO₂ (core) and p-type PPy (shell). The long chains of these p-n junctions in nanofibers result in the modification of the electronic band structure of PPy, leading to a reduction in the work function of the electrons. The significant surface structural modification in PPy/SnO₂ causes a prominent reduction in the 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-emission behavior and advantages of using such hybrid nanomaterials as compared to other composite nanomaterials have also been discussed in detail.