Static Secondary-ion Mass Spectrometry - Primary Operating Conditions

Primary Operating Conditions

Ion bombardment of a surface may result in a drastic change of its chemical composition and structure. These changes include sputtering, amorphization, implantation, diffusion, chemical reactions, and so on. All these changes are limited to a very small region surrounding the path of the primary ion into the solid. For Static SIMS each subsequent primary ion hits an undamaged area and total of only 0.1-1% of the atomic sites are bombarded during the measurement. To ensure this very low primary current densities are used generally in the range of 10−10 – 10−9 A/cm² (primary ion dose is below 1012 - 1013 ions/cm2). This leads to extremely small sputtering rates of fraction of a monolayer per hour and hence small secondary ion current density. Additionally, these emitted secondary ions are of low kinetic energy and emitted up to 20 nm from the impact site with surface annealing occurring in femto-seconds. These reasons make SSIMS a purely surface analysis technique causing negligible damage to the surface and with detection limit as low as 10−8 monolayer (ML).