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We describe resonant infrared pulsed laser deposition (RIR-PLD) of cyclic olefin copolymer, a barrier and protective layer; for comparison, we describe RIR-PLD of polystyrene and poly(ethylene dioxythiophene) about which we already have significant knowledge. Film deposition based on resonant infrared laser ablation is a low-temperature process leading to evaporation and deposition of intact molecules. In this paper, we focus on deposition of this model barrier and protective material that is potentially useful in the fabrication of organic light emitting diodes. The films were characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. We also compared the properties of films deposited by a free electron laser and a picosecond optical parametric oscillator.

We investigate the fundamental mechanisms of resonant-infrared laser ablation of polymers using polystyrene as a model material. Time-resolved plume shadowgraphy coupled with laser-induced temperature-rise calculations indicate that spinodal decomposition of a superheated surface layer is the primary mechanism for the initial stages of material removal. The majority of the ablated material is then released by way of recoil-induced ejection of liquid which proceeds for some tens of microseconds following a ~μs laser pulse excitation. The recoil-induced ejection of liquid material as the dominant ablation mechanism helps to explain previous observations of laser deposition of intact polymeric material.

Multi-layered polymer light-emitting diodes (PLEDs) have been fabricated in a vacuum environment by resonant infrared pulsed-laser deposition of the polymer layers. The light emitter used was poly[2-methoxy-5-(2- ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), and in some cases a layer of the hole-transport polymer poly(3,4 etylenedioxythiophene:polystyrenesulfonate) (PEDOT:PSS) was also laser deposited, resulting in a device structure of ITO/PEDOT:PSS/MEH-PPV/Al. Fourier transform infrared (FTIR) spectroscopy confirmed that neither of the laser-deposited polymers was significantly altered by the deposition process. Laser-fabricated devices displayed electroluminescent spectra similar to those of conventional spin-coated devices, but the differences in electrical characteristics and device efficiency were substantial. These discrepancies can probably be attributed to surface roughness of the deposited polymer layers. With the appropriate refinement of the deposition protocols, however, we believe that this process can be improved to a level that is suitable for routine fabrication of organic electronic components.

Polymer light emitting diodes (PLEDs) have been fabricated in a vacuum environment by resonant infrared laser ablation of the light emitting layer. The light emitting polymer used was poly[2-methoxy-5-(2-ethylhexyloxy)- 1,4-phenylenevinylene] (MEH-PPV) and was deposited into the device structure ITO/MEH-PPV/Al. Fourier transform infrared (FTIR) spectroscopy confirmed that the laser-deposited polymer was not drastically altered by the deposition process. Laser-fabricated devices displayed similar properties such as electroluminescence spectra and IV characteristics as conventional spin-coated devices. The dependence of these device properties on laser fluence was investigated, and showed no strong dependency. Peak emission wavelengths of electroluminescence spectra were all within 10 nm of electroluminescence spectra of spin coated devices and showed only slight peak broadening. These results are technologically important in that shadow mask technology can be incorporated into this method to arbitrarily pattern substrates with light emitting polymers.

Thin films of the conducting polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) were deposited by resonant infrared laser ablation. The PEDOT:PSS was frozen in various matrix solutions and deposited using a tunable, mid-infrared free-electron laser (FEL). The films so produced exhibited morphologies and conductivities that were highly dependent on the solvent matrix and laser irradiation wavelength used. When deposited from a native solution (5% by weight in water), as in matrix-assisted pulsed laser evaporation (MAPLE), films were rough and electrically insulating. When the matrix included other organic "co-matrices" that were doped into the solution prior to freezing, however, the resulting films were smooth and exhibited good electrical conductivity (0.2 S/cm), but only when the ablation was carried out at certain wavelengths. These results highlight the importance of the matrix/solute and matrix/laser interactions in the ablation process.

Experiments on pulsed laser vaporization of many different kinds of polymers have demonstrated that it is possible to eject intact polymers into the ambient, whether air or vacuum, by resonant pulsed laser excitation, using both neat and matrix targets. Two recent studies of resonant infrared ablation - one on polystyrene, the other on poly(amic acid), the precursor for the thermoset polyimide - show moreover that the ablation process is both wavelength selective and surprisingly non-energetic, especially compared to ultraviolet laser ablation. We propose a wavelength-selective photothermal mechanism involving breaking of intermolecular hydrogen bonds that is consistent with these observations.