开发一种有效的方法来稳定地提高量子效率(QE)并将Cu光电阴极的光发射阈值扩展到紫外线区域之外,可以使用于超快电子源应用的光注入器受益。2D材料保护层的实现被认为是延长光电阴极的工作寿命的有前途的方法。我们建议石墨烯可以在光电阴极材料和低功函数涂层之间的界面处用作中间层。氧在Cu表面的Cs/O活化过程中的作用被石墨烯中间层改变。此外,少层石墨烯(FLG)表面更有可能诱导Cs2O的形成。因此,通过Cs/O活化,石墨烯-Cu复合光电阴极可以实现低至0.878eV的超低表面功函数。具有FLG中间层的复合阴极的光发射性能显著增强。光电阴极具有对近红外区域的扩展光谱响应和更高的QE。在350nm,它的量化率是cessiated裸铜的两倍多,达到0.247%。降解后,石墨烯-Cu阴极可以通过再活化完全恢复,具有显著增强的稳定性。此外,复合阴极可以在超过4×10-6Pa的不良真空压力下可靠地运行。这项研究验证了将2D材料纳入光电阴极的新方法,提供新的方法来探索鲁棒和光谱扩展的光电阴极。
Developing an effective method to stably enhance the quantum efficiency (QE) and extend the photoemission threshold of Cu photocathodes beyond the ultraviolet region could benefit the photoinjector for ultrafast electron source applications. The implementation of a 2D material protective layer is considered a promising approach to extending the operating lifetime of photocathodes. We propose that
graphene can serve as an intermediate layer at the interface between photocathode material and low-work-function coating. The role of oxygen in the Cs/O activation process on the Cu surface is altered by the
graphene interlayer. Besides, the few-layer
graphene (FLG) surface could be more likely to induce the formation of Cs2O. Thus, the
graphene-Cu composite photocathode can achieve an ultralow surface work function of down to 0.878 eV through Cs/O activation. The photoemission performance of the composite cathode with a FLG interlayer is significantly enhanced. The photocathode has an extended spectral response to the near-infrared region and a higher QE. At 350 nm, its QE is more than twice that of the cesiated bare Cu, reaching 0.247%. After degradation, the
graphene-Cu cathode can be fully restored by reactivation, with remarkably enhanced stability. In addition, the composite cathode can be operated reliably under a poor vacuum pressure of over 4 × 10-6 Pa. This study validates a new method for incorporating 2D materials into photocathodes, offering novel approaches to explore robust and spectrum-extended photocathodes.