Monday, 11 October 2004 - 10:30 AM

This presentation is part of : Recent Progress in Laser-assisted Micro/Nanoprocessing

Pulsed Laser Deposition vs. Matrix Assisted Pulsed Laser Evaporation for Growth of Biodegradable Polymer Thin Films

James M. Fitz-Gerald, University of Virginia, University of Virginia, 116 Engineer's Way, Charlottesville, VA 22904

Thin films of a biodegradable polymer, poly (lactide-co-glycolide) (PLGA), were deposited onto Si substrates by both conventional pulsed laser deposition (PLD) and matrix assisted pulsed laser evaporation (MAPLE) using chloroform (CHCl3) as a matrix solvent. All depositions were conducted with an excimer laser (= 248 nm,  = 25 ns FWHM, 5 Hz) in Ar at 100 mTorr at laser energy densities ranging from 0.1 to 1 J/cm2. The deposited materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), and gel permeation chromatography (GPC) with refractive index (RI) detection. The results show that significant polymer degradation was observed for both methods with respect to changes in molecular weight. Optical transmission measurements of the starting MAPLE targets yielded laser penetration depths on the order of 0.362 cm and 0.209 cm for pure CHCl3 and 1 wt. % PLGA in CHCl3 respectively. Application of the Beer-Lambert relationship for laser energy deposition predicts a negligible temperature rise of less than 1 K at the target surface, which is in clear contradiction with ablation rates of 1.85 Ám / pulse experimentally measured for polymer loaded samples. With an ablation process of this magnitude, the material ejection is likely to have the character of laser spallation rather than evaporation, with a likely contribution of nonlinear or non-homogeneous laser light absorption. Severe non-uniformity of the final surface morphologies of the MAPLE films, similar to solvent wicking artifacts found in spin casting supports the spallation scenario.

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