PDMS patterning by proton beam S.Z. Szilasi a, * , R. Huszank a , A. Csik a , C. Cserháti b , I. Rajta a a Institute of Nuclear Research of the Hungarian Academy of Sciences, H-4026 Debrecen Bem tér 18/c, H-4001 Debrecen, P.O. Box 51, Hungary b University of Debrecen, Dept. of Solid State Physics, H-4010 Debrecen, P.O. Box 2, Hungary article info Available online 12 March 2009 PACS: 41.75.Ak 42.82.Cr 81.40.Lm 81.40.Wx 81.65.Cf 61.80.Jh 61.82.Pv 82.35.Lr Keywords: PDMS Proton beam micromachining (PBM) Proton beam writing (PBW) Irradiation abstract In this paper poly-(dimethylsiloxane) (PDMS) is introduced as a resist material for proton beam writing. We were looking for a biocompatible micropatternable polymer in which the chemical structure changes significantly due to proton beam exposure making the polymer suitable for proton beam writing. Up to now PDMS has been used as a casting or replicating material in microfabrication to form micro- channels, micromolds, microstamps, etc. PDMS has not been used as a resist material for direct write techniques. In this work we investigated the surface topography of the irradiated regions of PDMS under and without stress (on the cut surface and on the original fluid surface, respectively). In the samples wherein stress was not developed, noticeable compaction was observed. In the case of samples wherein stress was developed, noticeable swelling occurred. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction In recent years, rapid growth has been seen in research and development of bioanalytical devices, which is driven by the aggressive fusion of microfabrication technology and modern bio- technology. Because of the fast spreading lab-on-a-chip techniques the surface modification of biocompatible materials receives grow- ing attention. For microtechnology and biomedical research poly- mers are an interesting class of materials due to their many unique characteristics. In such fields PDMS has been widely used as a casting or repli- cating material due to its exceptional material properties [1,2]. Poly-(dimethylsiloxane) is a commonly used silicon-based or- ganic, cross-linkable polymer. It acts like a rubbery solid when it is cross-linked. In this state, the polymer does not permanently de- form under stress or strain and it is stable over a wide temperature range [3]. Due to the fact that PDMS is chemically inert and with certain chemical and/or physical treating the material can be turned into biocompatible [4], meaning that it has negligible toxic- ity, PDMS is used for the production of numerous active and pas- sive implantation devices that are in direct, and sometimes prolonged contact with human tissues [5,6]. The high oxygen permeability, good mechanical property, self- sealing property, convenient processing, and chemical stability of PDMS make it an ideal choice for creating various medical devices [7], such as ophthalmologic biomaterials, artificial lung [8] or arti- ficial finger joint [9]. Due to the high optical clarity, low attenuation, and the excel- lent stability against weathering PDMS is applicable for creating optical waveguides or microlenses [10,11]. It is also notably hydro- phobic, meaning that water cannot easily penetrate its surface. This property has led to extended use in microfluidics too [3,12]. PDMS is a versatile, widely used material in many fields of sci- ence, but it has been mainly used as a casting or replicating [13,14] material so far. Due to the numerous favourable characteristic this medium can be a possible biocompatible, implantable resist for PBW too, we decided to examine how it behaves under proton beam exposure. 2. Experimental All irradiations in this work have been performed at the nuclear microprobe facility at HAS-ATOMKI, Debrecen, Hungary [15]. The proton energy was 2 MeV in all exposures. SRIM [16] calculations 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.03.038 * Corresponding author. Tel.: +36 52 509 200; fax: +36 52 416 181. E-mail address: szilasi@atomki.hu (S.Z. Szilasi). Nuclear Instruments and Methods in Physics Research B 267 (2009) 2296–2298 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb