The Zr-O-W(100) emitter and coadsorption of zirconium and carbon monoxide on W(100)

Abstract

The properties of the Zr-O-W(100) emitter and the coadsorption of zirconium and carbon monoxide on W(100) have been studied by Auger electron spectroscopy and work function measurements. The thermionic work function of the Zr-O-W(100) emitter from 1450 to 1800 K is 2.54 eV with a pre-exponential value of 4. The field-emission retarding potential work function is 2.75–2.80 eV. A Zr-O-W(100) emitter free of bulk carbon possesses a longer lifetime than an emitter containing bulk carbon. Heating the emitter in carbon monoxide causes diffusion of zirconium into the bulk, and vacuum annealing restores the zirconium to the surface. The coadsorption of zirconium and carbon monoxide on W(100) followed by vacuum annealing produces a minimum work function of 2.3 eV. The adsorption sequence is important and lower work functions correlate with higher carbon concentrations. The stability of the 2.3 eV surface under background gas adsorption and high-temperature heating is discussed.