Application of a novel compact Cs evaporator prototype for enhancing negative ion yields during FIB-TOF-SIMS analysis in high vacuum

The potential of a novel caesium evaporator for enhancing negative secondary ion yields during Focused Ion Beam Time-Of-Flight Secondary Ion Mass Spectrometry (FIB-TOF-SIMS) elemental analysis is presented. The design of the lab prototype Cs evaporator is based on alkali metal dispensers containing a stable Cs salt and therefore it can be safely used for FIB-TOF-SIMS measurements under high vacuum conditions. Continuous insitu Cs-0 deposition on an Au sample surface has allowed the TOF-SIMS signal to be increased by a factor of 260, which confirms the functionality of the technique. A series of tests were conducted in positive and negative ion detection modes to study the response of the system to currents applied on Cs dispensers and generated Joule heating. A stable Cs flux (represented by a Cs+ signal measured with the TOF-SIMS) was achieved over around 1.5 h when using two Cs dispensers simultaneously. Moreover, the presence of Cs-0 has enabled the stability of an enhanced Si- signal measured by the TOF-SIMS to be maintained over several hours. This time is much longer than a typical duration of FIB-TOF-SIMS depth profiling, thus the presented method exhibits the potential for studying heterogeneous and multi-layer structures in a three-dimensional space.