Study of the exposure-dose-dependent photon-stimulated-desorption phenomena

Photon-stimulated desorption (PSD) was studied by using synchrotron light at a critical energy of 2.14 keV from the 1.5 GeV Taiwan Light Source. Samples of aluminum alloy (Al) and oxygen-free-high-conductivity copper (Cu) was studied at the 19B(PSD) beam line of the Synchrotron Radiation Research Center for exposure measurement. The yields of photoemission and the PSD are measured at different exposure beam doses. The result shows a decrease of the PSD yield for each gas and a decreased yield of photoemission at higher beam doses on the samples. The transient curves of pressure rise for each PSD molecule illustrate a longer delay time τ of the peak after exposing the surface with higher beam dose D. The delay time of $H2O$ and $O2$ are longer than that of CO, $CO2,$ $CH4,$ etc., in the case of both Al and Cu samples. In this work, it is found that $τ∼Dα,$ with $0.5<α<1,$ in cases where $D<2000 mA h.$ The discrepancy between the Al and Cu samples is not much different at higher beam doses. The processes of the chemical reactions by the photoelectrons and diffusion in the surface oxide layer are suspected to conduct the dose-dependent PSD phenomena.