Barbosa, L. G.

da Silva, M. R.

Papaléo, R.

Thomaz, R.

Trautmann, C.

GSI Repository

Irradiation-induced effects in organic thin PMMA filmsR. Thomaz1,2, C. Trautmann1,3, M. R. da Silva2, L. G. Barbosa2 and R. Papaléo21GSI, Darmstadt, Germany; 2 Pontifical Catholic University of Rio Grande do Sul, Brazil, 3Technische UniversitätDarmstadtIndividual heavy ions impacting insulators at high ve-locities (few tenths of MeV/u or higher) cause the ejectionof material and plastic deformation at the surface, result-ing in permanent rims and craters [1-4]. Recent studies onthe interaction of individual ions in polymeric thin filmsindicate that the surface effects are altered as the thick-ness of the material is reduced [5]. The effects of fast ionson confined structures are not completely understood [6]and may vary from those observed for bulk matter. In thiscontribution, we report on the impact features producedby 4.8 MeV/u Pb ions on poly(methyl methacrylate)(PMMA) films as a function of the thickness t at normalincidence. The results observed indicated a clear thick-ness dependent effect on the crater formation process forvery thin layers.Thin films of PMMA were spin-coated onto Si sub-strates with a thicknesses t ranging from 2 to 100 nm. Thefilms were bombarded with 4.8 MeV/u Pb ions at a flu-ence of ~108 cmí2 at the UNILAC accelerator. The sizeand shape of the surface tracks were characterized offlinewith a Nanoscope IIIa scanning force microscope (SFM).Figure 1: SFM images of PMMA films of indicated thick-ness, bombarded normal to the surface by 4.8 MeV/u Pb ions. The inset shows typical profile of impact features.Typical images of impact features at normal beam inci-dence are shown in Fig. 1. For the thicker films, two dif-ferent structures are observed at the impact site: crater-like holes and rims. Figure 2 and 3 depict quantitativedata on the averaged sizes of rims and craters as a func-tion of thickness t, respectively. For a critical thickness, the impact features show changes in size and morphol-ogy: below 40 nm, the rim volume decreases linearly anddisappears completely below t ~ 4 nm. This strong changeof rim dimension indicates a deeper depth of origin forprotrusion formation, related to long-range cooperativeinteractions. The crater dimensions on the other hand,showed only slight changes even for very thin samples,reducing from ~20 nm for thicker layers down to ~15 nmfor the thinnest films. The weaker thickness effect sug-gests their formation is very much dependent on the nearsurface excitation events, as was indicated recently by charge-state dependent impact craters produced with 600-MeV Au ions [5].Figure 2: Average volume of rims produced by4.8 MeV/u Pb ions and 3.0 MeV/u Au ions [5] on PMMAfilms of different thickness.Figure 3: Average diameter of craters produced by4.8 MeV/u Pb ions on PMMA films of different thickness.[1] F. Thibaudau et al., Phys Rev Lett. 67 (1991) 1582.[2] I. H. Wilson, Surf. Interface Anal. 20 (1993) 637.[3] R. Neumann, Nucl Instr. Meth B. 151 (1999) 42.[4] R.M. Papaléo, Transport Processes in Ion – Irradi-ated Polymers, in Surface tracks and cratering inpolymers (Berlin: Springer, 2004).[5] R. M. Papaleo, et al. Phys Rev Lett 101 (2008).[6] A.V. Krasheninnikov; K. Nordlund J. Appl. Phys.107 (2010).* Work supported by Brazilian agency CAPES.#R.Thomaz@gsi.deGSITemplate2007GSI SCIENTIFIC REPORT 2012 PNI-INHOUSE-EXP-32401

Irradiation-induced effects in organic thin PMMA films

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Irradiation-induced effects in organic thin PMMA films

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