Thin Solid Films 459 (2004) 318–322 0040-6090/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2003.12.139 High temperature ion beam erosion of polytetrafluoroethylene M. Adami , L. Guzman *, B.Y. Man , A. Miotello , P.M. Ossi a a, a a b INFM and Department of Physics, University of Trento, 38050, Povo (Trento), Italy a INFM and Department of Nuclear Engineering, Polytechnic of Milano, Italy b Abstract In this work we have studied the ion beam etching rates of PTFE by changing N-ion fluence at different sample temperatures. PTFE substrates were irradiated with 160 keV N ions to a dose range between 1=10 and 4=10 ionsycm . The treated 14 16 2 samples were examined by visible (514.5 nm) Raman spectroscopy as well as by scanning electron microscopy. Mechanical properties of the implanted layers were assessed by scratch-testing in conjunction with profilometry. Radiation cross-linking and polymer degradation by chain scission are competing processes in this type of polymer depending on the irradiation temperature. Flexible-chain polymers are easier to cross-link than rigid-chain polymers like PTFE, however, the latter can be cross-linked if temperature is high enough. It is shown that ion irradiation at room temperature even in the low dose range leads only to chain scission while at temperatures higher than the glass transition, evidence for cross-linking and consequent stiffening are found.  2003 Elsevier B.V. All rights reserved. PACS: 79.20.Rf Keywords: PTFE; Ion beam erosion; Microfabrication 1. Introduction Polytetrafluoroethylene (–CF –) is one of the most 2 n important materials in various kinds of industrial appli- cations in micromechanics and biomedical devices, based on its outstanding combination of chemical and physical properties such as excellent resistance to chem- ical reagents, high thermal stability, low friction coeffi- cient, biocompatibility, etc. However, PTFE is known to have high sensitivity to radiation, which limits its uses in many cases, typically for nuclear and space applica- tions. The mechanical properties are degraded due to chain scission even with small ion fluences. Recently, there has been increasing interest in the surface modifi- cation of PTFE to improve its properties. Many tech- niques have been applied, ranging from ‘wet’ chemical or electrical treatments, to plasma treatments, and par- ticle beam irradiation (electron, ion and photon) tech- niques w1–3x. In particular, cross-linking of PTFE was confirmed to occur by electron beam (EB) irradiation around the molten state (340 8C) under oxygen-free atmosphere w4x. High aspect-ratio microfabrication of *Corresponding author. Tel.: q39-0461-881-678; fax: q39-0461- 881-696. E-mail address: guzman@science.unitn.it (L. Guzman). in-situ (partially) cross-linked PTFE a surface was shown by Katoh w5x using synchrotron radiations. Although many efforts have been done on making microstructures of PTFE by pulsed laser ablation w6x, the aspect-ratio has still been small since PTFE exhibits almost no absorption from infrared to ultraviolet radia- tion. For properties of efficiently cross-linked PTFE, not only the radiation resistance but also mechanical prop- erties would be greatly improved. Ion beam irradiation is particularly attractive because of its flexibility, effectiveness, and environmentally friendly nature compared with conventional techniques, being suitable to modify the near-surface region of materials at low temperatures, thus avoiding any thermal degradation of the substrates. The modifications in the chemical structure and properties of polymers, induced by ion irradiation, were extensively studied; see for instance w7x. The use of ion irradiation is attractive since chemical composition and the related properties can be modified in a controlled manner by varying the ion dose or energy w8x. Generally, implantation into polymers works best in the low dose–low dose rate-high energy range since by working mostly in the regime of elec- tronic stopping it is possible to avoid degradation. Ion implantation has been successfully used to modify sev-