Proceedings Article | 15 September 2016
KEYWORDS: Pulsed laser deposition, Nanocomposites, Upconversion, Polymer thin films, Polymers, Molecules, Quantum efficiency, Ions, Polymethylmethacrylate, X-ray diffraction
There has been an explosive interest in the technique of laser assisted deposition of polymer nano-composite films
exploiting the matrix assisted pulsed laser evaporation (MAPLE) with regard to the polymer host as can be judged form
recent publications.1-4 In MAPLE, a frozen solution of a polymer in a relatively volatile solvent is used as a laser target.
The solvent and concentration are selected so that first, the polymer of interest can dissolve to form a dilute, particulate
free solution, second, the majority of the laser energy is initially absorbed by the solvent molecules and not by the solute
molecules, and third, there is no photochemical reaction between the solvent and the solute. The light-material
interaction in MAPLE can be described as a photothermal process. The photon energy absorbed by the solvent is
converted to thermal energy that causes the polymer to be heated but the solvent to vaporize. As the surface solvent
molecules are evaporated into the gas phase, polymer molecules are exposed at the gas-target matrix interface. The
polymer molecules attain sufficient kinetic energy through collective collisions with the evaporating solvent molecules,
to be transferred into the gas phase. By careful optimization of the MAPLE deposition conditions (laser wavelength,
repetition rate, solvent type, concentration, temperature, and background gas and gas pressure), this process can occur
without any significant polymer decomposition. The MAPLE process proceeds layer-by-layer, depleting the target of
solvent and polymer in the same concentration as the starting matrix. When a substrate is positioned directly in the path
of the plume, a coating starts to form from the evaporated polymer molecules, while the volatile solvent molecules are
evacuated by the pump from the deposition chamber. In case of fabrication of polymer nanocomposites, MAPLE targets
are usually prepared as nano-colloids of the additives of interest in the initial polymer solutions.
Mixing the components of different nature, organic polymers and inorganic dopants, in the same target at a certain
proportion and exposing them to the same laser beam not necessarily brings good quality nano-composite films. The
laser pulse energy and wavelength cannot be optimized for each component individually. Also, the mixing proportion in
the composite film is dictated by the initial proportion of the target and thus cannot be changed in the process. These
limitations were removed in the recently proposed method of multi-beam and multi-target deposition (in its doublebeam/
dual-target variation) using a MAPLE polymer target and one inorganic target, each being concurrently exposed to
laser beams of different wavelengths.5-14 Using the method, nano-composite films of polymer poly(methyl methacrylate)
known as PMMA doped with a rare earth (RE) inorganic upconversion phosphor compounds were prepared. Also, a
nano-composite film of thermoelectric film of inorganic aluminum-doped ZnO known as AZO was impregnated with
PMMA nano-fillers with the purpose of improving electrical conductivity and thermoelectric performance.10, 14 The
polymer target was a frozen (to a temperature of liquid nitrogen) PMMA solution in chlorobenzene exposed to a 1064-
nm laser beam from a Q-switched Nd:YAG pulsed laser. The inorganic targets were the pellets made of the compressed
micro-powders of highly efficient RE-doped NaYF4 or the sintered powder of AZO concurrently ablated with the
