Investigation of surface-conducted field emission from ZnO nanostructures as electron emitter in x-ray tube

Abstract

In recent years, x-ray generation could be achieved by using a cold cathode as the electron emitter has been reported by several groups. The cold cathode has also been regarded as a promising electron source of x-ray tube due to its intrinsic advantages. Some kinds of cold cathode such as carbon nanotube (CNT)-based field emission cathode show high current density and low turn on voltage. Though various sorts of electrode structures and material of field emission of the cold cathode used in x-ray tube have been widely researched, seldom reports have been concentrated on surface-conducted field emission (SCFE) cathode [1], especially on a planar triode with Zinc Oxide (ZnO) nanopin field emitters [2]. In 2007, C. Li et al. has reported a SCFE cathode made of ZnO nanotetrapod (ZNT) films with a current density of 0.6mA/cm2 [3]. Very recently, we have reported an improved SCFE cathode made of ZnO nanotetrapod and Magnesium Oxide (MgO) nanoparticle composite, whereas a current density of 4.7mA/cm2 is obtained (at a threshold bias electric field about 1v/μm) [4]. Although the threshold bias electric field we have reported about SCFE is low, the anode current density is not high enough, especially for x-ray tube application, there is still much room to improve. In this paper, we will present an improved SCFE cathode made of ZnO nanostructures with a current density of 25mA/cm2.