Matrix Assisted Pulsed Laser Evaporation (Maple) of Polymeric Materials: Methodology and Mechanistic Studies

A new matrix assisted pulsed laser evaporation (MAPLE) technique has been developed at the Naval Research Laboratory, to deposit superior quality ultra thin, and uniform films for a range of highly functionalized polymeric materials. The MAPLE technique is carried out in a vacuum chamber, and involves directing a pulsed laser beam onto a frozen target, consisting of a polymer dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, where both solvent and polymer molecules are lifted into the evacuated gas phase. A solvent and polymer plume are generated incident to the substrate being coated. Si(111), and NaCl substrates coated with thin layers of polymer have been examined by a range of techniques including: optical microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy. Under optimum conditions the native polymer was transferred to the substrate without chemical modification as a highly uniform film.The MAPLE technique offers a number of advantages over conventional polymer deposition techniques, including the ability to precisely and accurately coat a relatively large or small targeted area with an ultrathin, and uniform coating with sub monolayer thickness control. Conventional pulsed laser ablation techniques can be utilized for coating a limited number of polymers, but we have found that for highly functionalized materials the native polymer structure is almost completely lost in the process. In contrast, when the MAPLE conditions are optimized the deposition of even highly functionalized polymeric materials proceeds with little effect on the intrinsic polymer structure.