Potential field emitters: HfC nanorods sheathed with a HfO₂ nanoshell

Large-scale hafnium carbide (HfC) nanorods sheathed by a hafnium oxide (HfO₂) nanoshell were fabricated using a vacuum catalytic chemical vapor deposition (CVD) method in a HfCl₄-C₃H ₆-H₂-Ar system containing a small amount of oxygen impurities. The microstructures and morphologies of the products were characterized by an X-ray diffractometer, field-emission scanning electron microscope, transmission electron microscope, and energy-dispersive X-ray spectrometer. The results show that the synthesized needle-like nanostructures, with a diameter of ~100 nm and a length below 2 μm, consist of a HfC core and a HfO₂ shell with a thickness of ~5 nm surrounding the core. According to two comparative experiments, a growth mechanism is proposed to explain the formation of the nanorods through a combination of an oxygen-assisted growth process and a root-type vapor-liquid-solid process. The HfC nanorods exhibit excellent field emission (FE) properties with a low turn-on field of 3.2-3.4 V μm^-1, high field enhancement factor of 2335, and stable emission current density with a fluctuation below 5% over two hours.