In 1982, the first reports of laser ablation of polymers were issued almost simultaneously by Y. Kawamura et al.1 and R. Srinivasan et al.2 Srinivasan went on to become a leader in the field of polymer ablation. Srinivasan probably also coined the terms laser ablation and ablative photodecomposition, now in common use. The onset of material removal by laser ablation characteristically occurs at a well-defined laser fluence (energy per unit area). As the fluence is raised above this threshold, the ablation rate increases. The threshold fluence (F0 or Fth) is material and laser wavelength dependent and can vary from tens of mJ cm-2 to more than 1 J cm-2. The discovery of laser ablation of polymers sparked research in this field in many groups around the world. Many aspects of polymer ablation, and laser processing in general, are reviewed by Bauerle.3 Today, commercial applications of polymer laser ablation include the preparation of viaholes in polyimide for multichip modules at IBM4 and the production of inkjet printer nozzles (also polyimide).5 Considerable progress has been made in understanding polymer ablation since the last series of reviews a decade ago.6-8 New developments in polymer ablation include the application of femtosecond laser pulses, vacuum ultraviolet lasers (VUV), and free electron lasers (FEL). Some of these techniques have a great potential for the development of new applications and research tools. Much of this progress is discussed in this and other articles appearing in this special issue of Chemical Reviews. Current research on polymer ablation may be divided into two areas: (i) Applications of laser ablation, novel materials, and techniques. (ii) Studies of ablation mechanisms (databased modeling). The first area will be discussed in detail in this article, while the mechanistic aspects, especially the theoretical part, are discussed in other articles in this special issue. Many experimental methods and experimental polymers have been designed with a view toward improving our understanding of ablation mechanisms. It is often impossible to completely separate experiments designed to illuminate ablation mech† Paul Scherrer Institut. ‡ Washington State University. 453 Chem. Rev. 2003, 103, 453−485

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Chemical and spectroscopic aspects of polymer ablation: Special features and novel directions

Polymers have wide-ranging applications in food packaging and decorative products, and as insulation for electronic devices. For these applications, the adhesion of materials deposited onto polymer substrates is of primary importance. Not all polymer surfaces possess the required physical and/or chemical properties for good adhesion. Plasma treatment is one means of modifying polymer surfaces to improve adhesion while maintaining the desirable properties of the bulk material. This paper addresses the interaction of organic surfaces with the various components of a plasma, with examples taken from a review of the pertinent literature.

Plasma modification of polymer surfaces for adhesion improvement

Continued innovations in the polymer industry have made polymer surface modification methods a subject of intense research. The importance and necessity of surface modification of plastics are explained, and the advantages of physical surface treatments over the less-sophisticated chemical methods are outlined. Currently available physical surface modification methods for food packaging polymers are reviewed from the food packaging perspective. These physical surface modification methods include flame, corona discharge, UV, gamma-ray, electron beam, ion beam, plasma, and laser treatments. The principle of operation of each method is briefly described, and the advantages and disadvantages of each technique are cited. The extent to which each of these methods can produce the specific modifications desired is discussed. Furthermore, the effects of each treatment on barrier, mechanical, and adhesion properties of food packaging polymers are also examined. Finally, an overview of economic aspects of sophisticated surface modification techniques, including ion beam, plasma, and laser treatments, is presented.

Physical polymer surface modification methods and applications in food packaging polymers.

Fabrication of microfluidic devices by excimer laser ablation under different atmospheres may provide variations in polymer microchannel surface characteristics. The surface chemistry and electroosmotic (EO) mobility of polymer microchannels laser ablated under different atmospheres were studied by X-ray photoelectron spectroscopy and current monitoring mobility measurements, respectively. The ablated surfaces of PMMA were very similar to the native material, regardless of ablation atmospheres due to the negligible absorption of 248-nm light by that polymer. The substrates studied that exhibit nonnegligible absorption at this energy, namely, poly(ethylene terephthalate glycol), poly(vinyl chloride), and poly(carbonate), showed significant changes in surface chemistry and EO mobility when the ablation atmospheres were varied. Ablation of these three polymer substrates under nitrogen or argon resulted in low EO mobilities with a loss of the well-defined chemical structures of the native surfaces, while ablation under oxygen yielded surfaces that retained native chemical structures and supported higher EO mobilities.

Surface Characterization of Laser-Ablated Polymers Used for Microfluidics

Ultra-Water-Repellent Poly(ethylene terephthalate) Substrates

We have investigated by x‐ray photoelectron spectroscopy (XPS) the surface of two polymers [polytetrafluoroethylene and polyethyleneterepthalate (PTFE) and (PET)] which were previously submitted to pulsed UV radiation delivered from an excimer laser (ArF: λ=193 nm). Treatments realized under different gaseous atmospheres allow us to point out mechanisms leading to several chemical transformations at the polymer surface. In the case of PTFE, the high‐fluence irradiations produce defluorination with surface oxidation. The latter is mainly due to air moisture. The deposition of some ablated fragments on the surface has also been observed. For PET, the major modifications are produced below the ablation threshold. They are characterized by severe deoxidation due to the loss of CO and CO2. The irradiations under oxygen and nitrogen atmospheres show the possibility of grafting new functionalities at the polymer surface.

Polymer surface reactivity enhancement by ultraviolet ArF laser irradiation: An x‐ray photoelectron spectroscopy study of polytetrafluoroethylene and polyethyleneterepthalate ultraviolet treated surfaces

The characterization of surface modifications of polymers, after irradiation with X-ray or UV photons, is abundant in the XPS literature, reporting from core level analysis the modification of surface chemical composition (loss of fluorine, or chlorine, or oxygen … content). This work focuses on the use of XPS valence band spectra to show that irradiation can lead to superficial structural modification — lateral chain grafting, or crosslinking — of so-called “reactive” (polytetrafluoroethylene) and even more “stable” (polypropylene and polyethylene) polymers: this is best evidenced by modification of the typical shape of the C2s valence band. This structural modification appears more pronounced for high fluence UV excimer laser irradiation in air, than for (more moderate) exposition to harder X-rays in vacuo.

Excimer laser (λ = 193 nm) versus Al Kα X-ray damages on polymer surfaces: an XPS (core and valence levels) analysis of polytetrafluoroethylene, polypropylene and polyethylene

E. M. Roberfroid

Papers

Polymer surface reactivity enhancement by ultraviolet ArF laser irradiation: An x‐ray photoelectron spectroscopy study of polytetrafluoroethylene and polyethyleneterepthalate ultraviolet treated surfaces

Excimer laser (λ = 193 nm) versus Al Kα X-ray damages on polymer surfaces: an XPS (core and valence levels) analysis of polytetrafluoroethylene, polypropylene and polyethylene

Polyimide Surface Degradation: X-ray Photoelectron Spectroscopic Study Under UV-Pulsed Laser Irradiation