Vanina CRISTAUDO oral presentation (FN1-Mon4-2-1)
Effect of Nanoconfinement on the Sputter Yield
in Ultrathin Polymeric Films: Experiments and Models
Universite Catholique de Louvain, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium
Since the advent of Ar cluster sputter beams in secondary ion mass spectrometry (SIMS) , an extensive body of theoretical and experimental studies was devoted to the investigation of the effects of the cluster energy, nuclearity and incidence angle on the energy deposition and fragmentation of organic solids [2-4]. Additionally, the energy deposition pathways and the efficiency of ejection in organic solids were computationally investigated as a function of the sample thickness for molecular crystals (Langmuir-Blodgett multilayers on silver) . However, to our best knowledge, the effect of the thickness of ultrathin polymer layers on the sputtering efficiency upon massive Ar cluster bombardment has not been investigated yet.
This fundamental contribution on SIMS polymer depth-profiling by large argon clusters investigates the dependence of the sputter yield volume (Y) on the thickness (d) of ultrathin films as a function of the substrate nature, i.e. hard vs soft. For this purpose, thin films of polystyrene (PS) oligomers (~4 kDa) are spin-coated, respectively, onto silicon and poly (methyl methacrylate) supports and, then, bombarded by 10-keV Ar3000+ ions. The investigated thickness ranges from 15 to 230 nm. Additionally, the influence of the polymer molecular weight on Y(d) for PS thin films on Si is explored. The sputtering efficiency is found to be strongly dependent on the overlayer thickness, only in the case of the silicon substrate. A simple phenomenological model is proposed for the description of the thickness influence on the sputtering yield. MD simulations conducted on amorphous films of polyethylene-like oligomers (1.4 kDa)  of increasing thickness (from 2 to 20 nm), under comparable cluster bombardment conditions, predict a significant increase of the sputtering yield for ultrathin layers on rigid substrates, induced by energy confinement in the polymer, and support our phenomelogical model.
 C. M. Mahoney, Cluster secondary ion mass spectrometry: Principles and applications, John Wiley & Sons, New York, 2013.
 M. P. Seah, J. Phys. Chem. C 117(24), 2013, 12622.
 B. Czerwinski, L. Rzeznik, R. Paruch, B. J. Garrison, Z. Postawa, Nucl. Instruments Methods Phys. Res. Sect. B 269(14), 2011, 1578.
 A. Delcorte, M. Debongnie, J. Phys. Chem. C 119(46), 2015, 25868.
 L. Rzeznik, R. Paruch, B. Czerwinski, B., B. J. Garrison, Z. Postawa, Vacuum 83, 2009, S155.