Oxidation Resistance Improvement of Graphene-Oxide-Semiconductor Planar-Type Electron Sources Using h-BN as an Oxygen-Resistant, Electron-Transmissive Coating

Graphene–oxide–semiconductor (GOS) planar-type electron emission devices with a hexagonal boron nitride (h-BN) protective layer have demonstrated improved oxidation resistance while maintaining their emission performance. The devices with a monolayer or a multilayer (13 nm in thickness) h-BN protective layer can emit electrons even after oxygen plasma exposure (ashing). Remarkably, the device with a monolayer h-BN was able to emit electrons with a maximum efficiency of 11% after a 4-min ashing, showing that a thin h-BN protection layer can provide oxygen tolerance to GOS devices without a significant emission loss. The thicker multilayer h-BN imparted higher oxidation resistance to the device but with decreased emission efficiency compared with the device with monolayer h-BN. Thus, the use of h-BN necessitates a trade-off between the device’s emission performance and its oxidation resistance. In addition, the etching rate of h-BN by the oxygen plasma treatment was found to increase by exposure to air after the first plasma treatment, which indicates that the adherence of H2O to the surface of h-BN is one probable cause of h-BN etching during the ashing process.