Consideration of the threshold of secondary electrons in photoelectron yield spectroscopy (PYS)

The threshold of secondary electrons in photoelectron yield spectroscopy (PYS) was examined using numerical calculations based on Fowler's formula, and was measured on a Cu(111) surface as a function of the surface temperature. In the numerical calculations, the yields are affected by surface temperature at around the threshold. The yield to the power of 1/2 shows a linear relationship of over 0.04 eV per 100 K from the threshold as a function of energy. The estimated threshold shifts to a lower energy with increasing surface temperature, by 0.003 eV per 100 K. The estimated thresholds also decrease with increasing value of the multiplier of n in Fowler's formula. In experiments, the threshold of Cu(111) at room temperature is estimated to be 4.8 eV ± 0.05 eV. The amount of change in the threshold caused by variation in surface temperature is interpreted in terms of the effects of the intrinsic Fowler's formula and lattice expansion.