Electron emission can be utilised to measure the work function of the surface. However, the number of significant digits in the values obtained through thermionic-, field- and photo-emission techniques is typically just two or three. Here, we show that the number can go up to five when angle-resolved photoemission spectroscopy (ARPES) is applied. This owes to the capability of ARPES to detect the slowest photoelectrons that are directed only along the surface normal. By using a laser-based source, we optimised our setup for the slow photoelectrons and resolved the slowest-end cutoff of Au(111) with the sharpness not deteriorated by the bandwidth of light nor by Fermi-Dirac distribution. The work function was leveled within ±0.4 meV at least from 30 to 90 K and the surface aging was discerned as a meV shift of the work function. Our study opens the investigations into the fifth significant digit of the work function.

电子发射可用于测量表面的功函数。但是，通过热电子，场和光发射技术获得的值中的有效数字位数通常仅为2或3。在这里，我们表明，当应用角度分辨光发射光谱法（ARPES）时，该数目可以增加到五个。这归因于ARPES能够检测仅沿表面法线定向的最慢的光电子。通过使用基于激光的光源，我们优化了慢速光电子的设置，并解决了Au（111）的最慢端截止，其清晰度不会因光带宽或费米-狄拉克分布而恶化。至少在30至90 K范围内，功函的水平保持在±0.4 meV以内，并且表面老化被视为功函的meV位移。