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Abstract

Thermal electron emission has been a subject of extensive study in both scientific research and engineering applications. The energy distribution of the emitted electrons is an important property not only in terms of electron beam performance but also to elucidate the underlying emission physics. However, quantifying this key property experimentally has been particularly challenging for thermal emission. This is partly due to the inherent complexities of the emitter-energy analyzer system, and partly due to extrinsic energy broadening because of inter-particle coulombic interactions. The latter, in particular, may mask the emitter’s intrinsic energy distribution. This study experimentally investigates the energy distribution of thermally emitted electrons from a variety of materials. Particle tracing simulations help estimate the contribution of the different energy broadening mechanisms throughout the beam’s trajectory in the analyzer. The results indicate that the intrinsic energy distribution of the emitter can be identified through the measured signal within approximately a hundred meV. Particularly interesting is a distinctively narrow spread in the measured energy distribution for an yttria emitter. First-principles calculations are subsequently employed to study the electronic structure of yttria. It is suggested that the defective structure of the yttria lattice gives rise to possible impurity states in the material. These localized impurity states exhibit a sharp energy profile that may explain the narrow energy spread of the thermally emitted electrons. Conventional wisdom has been that the emitter’s electronic structure is largely washed out in thermal emission spectra. The present study challenges that notion and establishes a link between the emitter’s electronic structure and the measured energy spectra, thus connecting first-principles findings to experimental thermal energy distributions. The study thus advances our fundamental understanding of thermal emission phenomena and reveals a novel approach to creating high-performance thermal emitters by engineering the electronic structure of the emitter material.