Growth of organic thin films by the matrix assisted pulsed laser evaporation (MAPLE) technique

Abstract

A novel variation of conventional pulsed laser evaporation, known as matrix assisted pulsed laser evaporation, or MAPLE, has been successfully used to deposit highly uniform thin films of a variety of organic materials including a number of polymers. The MAPLE technique is carried out in a vacuum chamber and involves directing a pulsed laser beam (λ=193 or 248 nm; fluence=0.01 to 0.5 J/cm2) onto a frozen target (100–200 K) consisting of a solute polymeric or organic compound dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, with both solvent and solute molecules being released into the chamber. The volatile solvent is pumped away, whereas the polymer/organic molecules coat the substrate. Thin uniform films (<50 nm) of various materials, such as functionalized polysiloxanes and carbohydrates, have been deposited on Si(111) and NaCl substrates. The films prepared using this method have been examined by optical microscopy, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and electrospray mass spectrometry. Careful control of the processing conditions allowed the complex polymer/organic molecules to be transferred to the substrate as uniform films without any significant chemical modification. Using MAPLE, large or small regions within a substrate can be discretely coated with submonolayer thickness control. The use of MAPLE films for chemical sensor applications has been investigated and the potential of this technique for producing high quality thin films of other organic compounds will be discussed.