Cross Sections of Electron Detachment for Si^- and Ge^- in Collision with Ar

Single electron detachment cross section for 10--40 keV Si^- and Ge^- in collisions with Ar are measured and compared with other available experimental results. In our experimental energy region, the trend of cross sections is almost constant. The cross sections of Ge larger than Si can be understood by including electron affinity and size of negative ions.