Pulsed laser deposition of super hydrophobic thin films of layered double hydroxides

A. Matei, R. Birjega, A. Vlad, M. Filipescu, R. Zavoianu, O.D. Pavel, M.C. Corobea, M. Dinescu
National Institute for Lasers, Plasma and Radiation Physics,
Romania

Keywords: thin films, layered double hydroxides, pulsed laser deposition, matrix assisted pulsed laser evaporation

Summary:

Pulsed Laser Deposition (PLD) and Matrix Assisted Pulsed Laser Evaporation (MAPLE) were employed for the deposition of lamellar - layered double hydroxides (LDH) thin films. Pressed pellets of Mg/Al LDH (Mg2.5Al(OH)7(CO3)0,5 • 2,5H2O = HT2.5) were used as targets for PLD experiments. Aqueous solutions of LDH were frozen and used as targets for MAPLE depositions. In order to tailor the wetting capabilities of the films, fatty acids as lauric or stearic acids were intercalated in the lamellar structure of the LDH powders and than the outcome composite products used as targets for PLD. Composite fatty acids-LDH powders in a mixture of water and ethanol (1:1 w/w) solutions were frozen in liquid nitrogen and used as targets for MAPLE depositions. The first (1064 nm), second (532 nm) and fourth harmonics (266 nm) of a Nd:YAG laser working at a repetition rate of 10 Hz were used for the ablation of the target. For 1064 nm wavelength, the pulse duration is 5-7 ns, while for the other harmonics the pulse duration is 4-6 ns. We have also performed experiments with an ArF excimer laser emitting at 193 nm with pulse duration of ~20 ns. The laser fluence was between 1.5 and 2 J/cm2. The targets were ablated by 10,000 – 40,000 pulses in order to evidence thin film thickness dependence to its morphology and wetting properties. The laser wavelength for MAPLE was 266 nm and the laser conditions and the number of pulses were the same as for PLD. The influence of the deposition parameters and fatty acids presence onto the films structural and morphological properties is presented and discussed. We have obtained hydrophobic and superhydrophobic surfaces for LDH & LDH-fatty acids films deposited by PLD and we have found that the growth mechanism depends strongly on the laser wavelength (1064, 532, 266 and 193 nm). The use of laser techniques leads to oriented films, with good adherence and controlled thickness, which represents a major advantage compared to other classical methods. Contact angles with values higher than 160º were measured on samples containing lauric acid in the interlayer space. The as deposited films can be further used as protective coatings in order to reduce the cost of metal and metal alloys corrosion. Chemical and thermal analysis, X-ray diffraction, IR spectroscopy, scanning electron microscopy, atomic force microscopy and contact angle measurements were the techniques used for the characterization of deposited thin films.