Suppression of Charging Effect by Ambient Pressure Hard X-ray Photoelectron Spectroscopy

Abstract

Charging effect suppression is a critical technique for accurate X-ray photoelectron spectroscopy (XPS) analysis of insulating materials. This study investigated how to reduce charging effects using ambient-pressure hard X-ray photoelectron spectroscopy (AP-HAXPES) at SPring-8 BL46XU by introducing N2 or Ar gas. The relationship among gas pressure, binding energy (BE) shifts, and sample current was evaluated using an ungrounded Au plate. Increasing the gas pressure neutralized the positive charging effect by generating secondary electrons through gas ionization. For both N2 and Ar, higher pressures caused the sample current to switch from positive to negative, indicating excessive charge compensation. Specifically, excessive Ar gas pressure shifted the Au 4f7/2 BE below the grounded reference value of 84.0 eV. Simulations qualitatively supported these results, demonstrating that the total sample current is a sum of multiple components, including photoemission and gas-phase plasma generation. These findings indicate that achieving perfect charge neutrality is not easily done by simply increasing pressure, as excessive gas causes excessive charge compensation, requiring caution in AP-HAXPES measurements.