Structure, transport and field-emission properties of compound nanotubes: CNx vs. BNCx (x<0.1)

Abstract

Transport and field-emission properties of assynthesized CNx and BNCx (x < 0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CNx nanotubes displayed well-defined metallic behavior and low resistivities of ∼ 10-100 kΩ or less at room temperature, whereas those made of BNCx nanotubes exhibited semiconducting properties and high resistivities of ∼ 50-300 MΩ. Both types of ropes revealed good field-emission properties with emitting currents per rope reaching ∼ 4 μA (CNx) and ∼ 2 μA (BNCx), albeit the latter ropes severely deteriorated during the field emission. Macrofilms made of randomly oriented CNx or BNCx nanotubes displayed low and similar turn-on fields of ∼ 2-3 V/μm. 3 mA/cm2 (BNCx) and 5.5 mA/cm2 (CNx) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2-0.4 mA/cm2 both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing the current density to 0.2-0.4 A/cm2, only CNx films continued to emit steadily, while the field emission from BNCx nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating.