Matrix-assisted pulsed laser deposition of polymer and nanoparticle films A.P. Caricato a, * , A. Luches a , G. Leggieri a , M. Martino a , R. Rella b a University of Salento, Department of Physics, Via Arnesano, 73100 Lecce, Italy b Institute for Microelectronics and Microsystems, IMM-CNR, Via Monteroni, 73100 Lecce, Italy Keywords: Pulsed laser ablation Matrix-assisted PLD Polymers Nanoparticles Sensors abstract Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was used to deposit films of Poly(9,9- dioctylfluorene) e PFO and Methoxy Ge Triphenylcorrole [Ge(TPC)OCH3]. The PFO was dissolved in different matrices, like chloroform-CHCl3, tetrahydrofuran e THF and toluene with a 0.5 wt % concen- tration, while Ge(TPC)OCH3 was diluted in THF with a concentration of 0.01 wt %. The frozen targets were irradiated with a KrF excimer laser. The, films presented good emission properties to be exploited in light emitting devices and gas sensors based on luminescence quenching. The working principle of the MAPLE technique was used for the deposition of colloidal nanoparticles and nanorods, too. TiO2 colloidal nanoparticles (diameter: w10 nm) and nanorods (diameter: 5 nm; length: 50 nm) were diluted in deionised water (0.02 wt %) and toluene (0.016 wt %) respectively. The deposited nanostructures preserved dimensions and structural properties of the starting particles and the films showed very interesting electrical responses when exposed to oxidizing gases for sensing applications. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Great interest is growing about deposition and applications of thin films of polymers, organic materials and biomaterials. The goal is the realization of controlled nanostructures to be used, for instance, for drug delivery and tissue engineering [1], for gas and vapor detection [2], for light emitting devices [3], etc. Laser-based deposition techniques present advantages for thin film growth: monolayer thickness control, good film-to-substrate adhesion, minimum material consumption, low substrate temperature, stoi- chiometry preservation, among others. Pulsed laser deposition (PLD) is a well-known and powerful deposition method but, due to the high energy of the laser pulses, it is not well suited for the deposition of complex molecules like polymers and biomaterials. To avoid photochemical damage and decomposition caused by PLD, the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique was introduced [4]. MAPLE is a modification of the PLD technique. The main difference is the target structure: the material of interest (solute) is diluted in a volatile solvent matrix to form a homoge- neous solution (solute concentrations typically up to several wt %). The solution is frozen at liquid nitrogen temperature (LNT) and then rapidly placed into a vacuum chamber to act as a target for the laser assisted deposition. The pulsed laser energy is mainly absorbed by the solvent and converted to thermal energy, allowing the solvent to vaporize. By collective collisions with the evaporating solvent, the molecules of the solute material receive enough kinetic energy to be transferred in the gas phase and deposited as thin films on suitable substrates. The solvent is mostly pumped away during the flight from the target to the substrate. Since most of the laser energy is absorbed by the volatile matrix rather than by the solute molecules, their photochemical decomposition is mini- mized. The ablation onset is defined by the thermodynamic parameters of the volatile solvent, rather than by the ones of the solute material, so depositions can proceed at lower fluences (0.05e0.5 J/cm 2 ), as compared to conventional PLD (a few J/cm 2 ). Moreover, in principle MAPLE, allows a fine thickness control of polymeric films, beyond the limits of spin coating and drop casting techniques. We used the MAPLE technique to deposit films of polymers. Here, some results of the deposited PFO and Ge(TPC)OCH3 films are given. Moreover, a new application, MAPLE deposition of TiO 2 nanoparticle and nanorod films will be introduced. 2. MAPLE deposition apparatus The MAPLE deposition hardware does not substantially differ from the one used in PLD. The main difference is the target holder, since it has to be kept al low temperature. It means that a liquid nitrogen reservoir must be connected to the target holder. It is usually made of high conductivity oxygen free copper, crossed by * Corresponding author. Fax: þ39 832297499. E-mail address: caricato@le.infn.it (A.P. Caricato). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2011.07.046 Vacuum 86 (2012) 661e666