Experimental and numerical study of submonolayer sputter deposition of polystyrene fragments on silver for the...

In static secondary ion mass spectrometry (SIMS), quantification and high ionization probabilities are difficult to obtain. The Storing Matter technique has been developed to circumvent these issues and has already been applied to deposit inorganic and organic samples. For organic samples, the effect of fragmentation during sputter deposition and changing coverage on time-of-flight (TOF)-SIMS mass spectra has not been investigated. In this work, polystyrene (PS) was sputter deposited on silver using an argon ion beam in order to investigate these parameters and to get a better control of the whole process. For this purpose, we introduce a multitechnique characterization approach for the submonolayer deposition of PS. Experimental methods (TOF-SIMS, X-ray photoelectron spectroscopy (XPS)) were used in combination with simulations (density functional theory (DFT) calculations) in order to obtain information about the molecular and structural changes and the interactions of organic matter with the metal surface. Alterations of the PS surface and PS sputter deposit as a function of surface coverage and Ar(+) ion fluence are addressed. A major finding is that this approach can be used to identify surface reactions between different fragments on the collector surface. Indeed, in the dynamic regime, the ratio of large to small fragments is increasing although the fragmentation during the sputter deposition should lead to increasingly smaller fragments. Hence, for Storing Matter, the coverage on the collector must be kept low in order to minimize the reactions between fragments and to preserve the information on the original sample.