Vacuum 82 (2008) 232–235 Plasma processing for surface optical modiﬁcations of PET ﬁlms Paola Esena Ã , S Zanini, C. Riccardi Dipartimento di Fisica Occhialini, Universita` degli Studi di Milano-Bicocca, p.za della Scienza, 3-20126 Milano, Italy Abstract The plasma interaction with the surface produces modiﬁcations of its chemical structure or morphology. Surface modiﬁcations through cold plasma occur, thanks to the high plasma reactivity and ability to affect the surface of materials. The present work shows the surface modiﬁcation of polyethylene terephthalate (PET) ﬁlms after the exposure both to low-pressure plasma (ﬁlm deposition by plasma enhanced chemical vapour deposition) and to an atmospheric pressure dielectric barrier discharge (surface etching). After plasma treatment we have analysed the effect on the PET surface. For the atmospheric pressure plasma-treated samples, contact angle and atomic force microscope analysis enable us to determine roughness changes. For the low-pressure plasma samples, contact angles and Fourier transform infrared absorption spectroscopy analysis are used to estimate the chemical composition of the deposition and focused ion beam analysis to collect the image and calculate the thickness of plasma deposition. Both plasma treatments (ﬁlm deposition and etching) cause changes in optical properties as indicated by reﬂectivity measurements. r 2007 Elsevier Ltd. All rights reserved. Keywords: Plasma processes; PET; Optical modiﬁcations; Reﬂectivity; Deposition; Etching 1. Introduction Plasma processing of materials is a quickly developing area of applied physics. In particular, low-pressure plasma treatments have been proposed in order to modify many surface properties of polymers such as adhesivity, hydro- phobicity, oleophobicity and hydrophilicity [1]. In particular, surface effects on polyethylene terephtha- late (PET) ﬁlms are of great interest in packaging industry to increase wettability and printability and to enhance antireﬂective or reﬂective properties [2]; compared with conventional chemical treatments cold plasma techniques have the advantages of being eco-friendly by keeping bulk properties unchanged. 2. Experimental 2.1. Material Samples of PET were provided by Neograf s.r.l. and consist of transparent ﬁlms with grammature of 16.8 g/m 2 and thickness of 12 mm. Prior to treatments, PET speci- mens were ultrasonically washed in ethanol and deionised water. 2.2. Apparatus Low-pressure plasma treatments were applied for hexamethyldisiloxane (HMDSO) deposition and the dis- charges have been generated in a low-pressure, capacitively coupled radiofrequency (RF) plasma reactor. The plasma is produced inside a cylindrical stainless steel vacuum chamber (diameter 200 mm) with several ports for gas inlet and diagnostics. Before operating the discharge device is evacuated up to a residual pressure of 10 5 mbar by means of a turbo-molecular pump (Turbovac 150 V) in turn evacuated by a rotary pump (Varian SD300). Afterwards HMDSO is injected through a micrometer valve. After reaching the desired initial pressure (1 mbar) the micro- meter valve is closed. A Pirani Gauge (Varian SenTorr) records the pressure, given in N 2 equivalent, the absolute calibration for HMDSO being not precisely known. RF power is delivered to the discharge by a RF antenna consisting of a stainless steel circular plate (180 mm diameter). The antenna is externally connected, through a ARTICLE IN PRESS www.elsevier.com/locate/vacuum 0042-207X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.07.054 Ã Corresponding author. Tel.: +39 02 64482327; fax: +39 02 64482317. E-mail address: paola.esena@mib.infn.it (P. Esena).