Thermally stimulated exoelectron emission from graphite surfaces exposed to oxygen, tetrafluoromethane, and argon plasmas

We have investigated the thermally stimulated exoelectron emission (TSEE) from graphite surfaces exposed to O2, CF4, and Ar plasmas in combination with the measurements of surface potential (SP) and x‐ray photoelectron spectroscopy (XPS). The surfaces exposed to the plasmas were left in the ambient air prior to the measurements. The TSEE glow curves, the change in SP, and the XPS spectra were examined as a function of plasma exposure time and pressure. The TSEE glow curves for each plasma gas exhibited one sharp emission peak (peak I) at ∼98 °C, the intensity of peak I decreasing in the order, O2≳CF4≳Ar. Furthermore, for CF4 plasma a broad peak (peak II) was also observed at ∼250 °C. The SP for the surfaces exposed to the plasmas became highly negative, decreasing in the order, Ar≳O2≳CF4. This can be attributed to an increase in the O and F contents on the surface. The change in SP after the plasma treatment was nearly reversed to the original value in each case after the TSEE measurement. The origins for...