Revealing the mechanism of conductive capping materials induced charge compensation in X-ray photoelectron spectroscopy analysis

Chueh Cheng Yang^1*, Meng-Hsuan Tsai², Zong-Ren Yang², Yaw-Wen Yang², Yuan-Chieh Tseng¹, Chia-Hsin Wang²

¹Department of Materials Science & Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²National Synchrotron Radiation Research Center, Hsinchu, Taiwan

* Presenter:Chueh Cheng Yang, email:amaranth.mse07g@nctu.edu.tw

The charging effect of insulating materials had been a long-lasting issue when measuring X-ray photoelectron spectroscopy (XPS). As the conventional methods, such as surface coating and electron flood gun, had been proved to be effective when measuring spectra, the balance between compensation and signal measurement is still hard to achieve. Owing to the development of ambient pressure XPS, we can now probe the charging surface properly with the compensation of gas introduction. However, the gas inlet also attenuates the signal intensity whereas failing to neutralize the charging surface as high flux X-ray source was applied. In this work, we demonstrate that the positively surface charging can be fully neutralized by a monolayer of graphene, which provides minimum amounts of signal attenuation. As we put a suspending screen which was electrically isolated to the surface, the surface could be neutralized at different level by tuning the distance between the sample surface and screen with various density. These phenomena allow us to propose the mechanism of surface potential neutralization. As the photo-, Auger and secondary electrons generated from capping materials after X-ray exposure, those ‘stray’ electrons could improve the spectrum after approaching the charging surface. Mechanism for surface charging neutralization was proposed since the fully compensation could be reach only with the directly covered graphene. The combination of electrons induced by X-ray and from the delocalized electron from graphene helps compensating the charging effect. This method could be applied to a wide range of energy source, especially surface sensitive techniques as the minimum attenuation of signals was achieved.

Keywords: Ambient Pressure XPS, Graphene, Charge compensation