MEASUREMENT OF SPECIMEN CHARGING IN SCANNING ELECTRON-MICROSCOPY WITHA KELVIN PROBE

A vibrating Kelvin probe in form of a platinum wire loop is used to me asure the surface potential Us on electron-irradiated free-floating me tal and insulator specimens as a function of electron energy E. This a llows an accurate measurement of the critical electron energy E2 for n o charging. At energies below E2, the positive charging increases with decreasing energy to U(s) = 2-5 eV at E = 0.5 keV and switching off t he collector bias of the Everhart-Thornley detector. A two- to threefo ld increase of U is observed when the bias is switched on. For E > E2, the strong increase of a negative surface potential can be measured. Insulating films free-supported on a conductive substrate show a steep decrease to small positive and negative Us when the film thickness be comes lower than the electron range at a critical energy E3 > E2. At i nsulating specimen the temporal decrease of charging can be measured w hen the electron beam is switched off.