Effects of sample-aperture cone distance on the environmental charge compensation in near-ambient pressure hard X-ray photoemission spectroscopy

Charging effect of insulating samples is a major problem in photoemission spectroscopy. Herein, the charging of a LiNbO3 wafer and glass plate was compensated by introducing nitrogen gas using a near-ambient pressure hard X-ray photoemission spectroscopy apparatus. This is because the secondary electrons created by electron scattering in the gas neutralized the charge on the sample surface. Moreover, the pressure required to compensate for the charging was found to strongly depend on the distance (d) between the sample surface and the aperture cone of the electron energy analyzer. At a normal distance of d= 0.3 mm, a pressure of 2500 Pa was required to compensate for the charging of the insulating samples. However, at d= 2.1 mm, the required pressure was reduced to only 250 Pa. The large d dependence of distance can be attributed to that electron scattering is largely disturbed by the aperture cone at small d values.