A moderate synthesis route of 5.6 mA-current LaB6 nanowire film with recoverable emission performance towards cold cathode electron source applications

Abstract

Lanthanum hexaboride (LaB₆) nanostructures have attracted much attention in recent years because they exhibit high electrical conductivity and thermal conductivity, low work function and high chemical stability, and can be expected to be an ideal cold cathode electron source for power device applications. Although some groups have developed means to grow LaB₆ nanostructures and investigated their emission properties, the moderate synthesis of the LaB₆ nanostructure cathode with high-performance is still a challenging issue. Here we developed a simple one-step chemical vapour deposition (CVD) method to prepare the LaB₆ nanowire cold cathode film. The LaB₆ nanowires have a mean length of tens of micrometres and their average diameter is about 100 nm. The formation of the nanowires is attributed to the synergy of the vapour–liquid–solid (VLS) and vapour–solid (VS) mechanisms. The LaB₆ nanowires are found to have a low turn-on (2.2 V μm⁻¹) and threshold field (2.9 V μm⁻¹) as well as nice field emission (FE) stability with a current fluctuation of only 1.7%. And their emission current can reach 5.6 mA (16.7 mA cm⁻²) at 4.1 V μm⁻¹, which is large enough for the high-current requirements of cathodes used in power devices. Moreover, the LaB₆ nanowires still retain excellent performance even if the operation temperature is raised up to 773 K. It is noted that the LaB₆ nanowire film exhibits quite different emission behaviours during a temperature cycling between room temperature and 773 K. The adsorption and desorption of oxygen onto and from the nanowire's surface is suggested to explain the discrepancy of such emission properties based on a series of our designed experiments. Most importantly, the LaB₆ nanowire cathode film can almost recover to the original excellent FE performances after detachment of the surface oxygen molecules, which suggests that they should be ideal cathode nanomaterials for power device applications.