Evaporation of a small amount of gold onto polymers : effects on surface morphology and signal enhancement in static SIMS

(eng) In static secondary ion mass spectrometry (s-SIMS), several more or less sample-restraint methods of secondary ion yield enhancement have been proposed. One of those methods is called Metal-Assisted SIMS (MetA-SIMS) and consists in a deposition of a small amount of noble metal onto the organic sample in order to enhance the characteristic secondary ion fragment intensities. In contrast to other MetA-SIMS studies, the metallization of the high-mass polymers was carried out in a preparation chamber, which is directly connected to the ToF-SIMS. This in situ metallization allows reducing the surface contamination and atmospheric influences to a minimum during sample manipulation/transportation. Beyond the secondary ion yield enhancement measured in ToF-SIMS, the exact deposited gold quantity was determined by XPS and a detailed characterization of the sample surface was accomplished by SEM and TEM. The aim of this work was two folded: From a purely analytical point of view, it was tried to find out the optimal conditions for the metallization of various and widely used polymers in order to maximize the secondary ion intensities in MetA-SIMS. A more theoretical aspect was to get further fundamental insights in the secondary ion emission process in MetA-SIMS. By dint of the morphology results, a model explaining the observed yield enhancement of the characteristic polymer fragments during atomic primary ion bombardment for low gold coverage was developed. The model takes into account that the polymer quantity at the sample surface diminish due to the deposited gold and suggests that the secondary ion yield enhancement mainly occurs near the polymer/gold interface. However for larger gold coverage, additional factors need to be determined in order to completely describe the yield enhancement in ToF SIMS.