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

Abstract

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 (SnO 2 )-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 SnO 2 nanoparticles of size ∼15 nm. These SnO 2 nanoparticles act as nucleation sites for the growth of PPy nanofibers, resulting in encapsulated SnO 2 nanoparticles in the PPy amorphous matrix. The coupling of spherical-shaped core–shell structures of PPy/SnO 2 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 SnO 2 (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/SnO 2 causes a prominent reduction in the turn-on electric field for electron emission in PPy/SnO 2 nanocomposite (∼1.5 V/μm) as compared to the pure PPy (∼3.3 V/μm) without significant loss in current density (∼1 mA/cm 2 ). 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.

Schottky DC generators from polypyrrole nanocomposites of N-type semiconductor metal oxides and the multiple device connection effect

“…Therefore, a stronger charge center formed within the PPy-SnO 2 composite, which facilitates electron hopping and thus improves electrical conductivity. 30 This is in agreement with the results of the dielectric constant.…”

“…The peaks at 1033 cm −1 and 773 cm −1 were assigned to C-H in-plane deformation and out-of-plane bending vibrations. 19,20,29,30 During the synthesis of the PPy composites, 5 wt%, 7.5 wt%, 10 wt%, 12.5 wt%, 15 wt%, and 20 wt% metal oxide (based on pyrrole) were added separately to the reaction. However, the actual metal oxide content in PPy, measured by ICP-OES, showed a certain deviation from the synthesis conditions (see details in Fig.…”

“…CeO 2 , WO 3 , and SnO 2 are n-type semiconductors capable of forming heterojunctions with PPy because of the p-type semiconductor nature of PPy. 30,41,42 Fig. 3b illustrates the energy structure of the PPy-metal oxide heterojunction.…”

“…The peaks at 1033 cm −1 and 773 cm −1 were assigned to C–H in-plane deformation and out-of-plane bending vibrations. 19,20,29,30…”

Generalizing Fowler–Nordheim Tunneling Theory for an Arbitrary Power Law Barrier

“…Field-emission electron sources with low-turn-on electric fields, high-emission current density, and good stability have a considerable role in expansive usage as sources for electron microscopes and in special vacuum nanoelectronic equipment. [5] Development of micro-and nanotechnology [6,7] inspired further development of experiments as well as the theory. In a canonical approach, a perfectly flat, conducting surface has been considered.…”