Applied Surface Science 302 (2014) 19–23 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Palladium nanoparticles produced by CW and pulsed laser ablation in water M. Boutinguiza a,∗ , R. Comesa ˜ na b , F. Lusqui ˜ nos a , A. Riveiro a,c , J. del Val a , J. Pou a a Applied Physics Department, University of Vigo EEI, Lagoas-Marcosende, 9, Vigo 36310, Spain b Materials Engineering, Applied Mechanics and Construction Department, University of Vigo, EEI, Lagoas-Marcosende, Vigo 36310, Spain c Centro Universitario de la Defensa, Escuela Naval Militar, Plaza de Espa˜ na 2, 36920 Marín, Spain a r t i c l e i n f o Article history: Received 29 June 2013 Received in revised form 13 January 2014 Accepted 14 January 2014 Available online 25 January 2014 Keywords: Palladium nanoparticles Laser ablation CW laser Pulsed laser a b s t r a c t Palladium nanoparticles are receiving important interest due to its application as catalyst. In this work Pd nanoparticles have been obtained by ablating a Pd target submerged in de-ionized using both, pulsed as well as continuous wave (CW) laser. The influence of laser parameters involved in the formation in nanoparticles has been studied. Crystalline phases, morphology and optical properties of the obtained colloidal nanoparticles were characterized by means of transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV/vis absorption spectroscopy. The obtained colloidal suspensions consisted of pure Pd nanoparticles showing spherical shape with diameters ran- ging from few nanometers to 5–60 nm. The moderate irradiance delivered by the CW laser favours high production of uniform nanoparticles. © 2014 Elsevier B.V. All rights reserved. 1. Introduction There’s an increase interest in metal nanoparticles because of their unique physical and chemical properties related to the size effect when compared to bulk material. Due to their special prop- erties, palladium nanoparticles play an important role in many industrial applications, such as, catalytic for organic reactions and in the reduction of automobile pollutants [1–3]. Their special sensi- tivity to absorb hydrogen make them good candidate as gas sensor and as hydrogen storage materials, in fuel cells or batteries [4–6]. For these applications it is important to synthesize nanoparticles with the adequate size distribution, morphology and crystallinity. There are different techniques for producing Pd nanoparticles, chemical, electrochemical, sonochemical, etc. [7–10]. Many of these techniques of production use precursors and solvents, or imply chemical reactions which can contaminate the obtained nanopar- ticles. Laser ablation of solids in liquids (LASL) enables obtaining nanoparticles with no need of chemical precursors. Its simplicity together with the advantage of producing nanoparticles with small size, narrow distribution and weak agglomeration make it suitable for metal nanoparticle fabrication. Pd nanoparticles have already been obtained by the LASL method using pulsed lasers, especially nanosecond and femtosecond lasers [11–13]. However nanoparti- cles can be synthesized in aqueous medium not only by the use ∗ Corresponding author. Tel.: +34 986812216. E-mail address: mohamed@uvigo.es (M. Boutinguiza). of pulsed laser but also using a CW laser. In previous works we have used CW laser delivering moderate irradiance to produce TiO 2 nanoparticles in liquids [14,15]. In the present work we report the synthesis of Pd nanoparticles using a pulsed laser as well as a CW one. The results are discussed and compared. 2. Experimental Plates of Pd with 99.99% of purity were cleaned and sonicated to be ablated by laser in water. The targets were attached to a bot- tom of a glass vessel and filled with distilled water up to 1 mm over the upper surface of the Pd plate. The first system used was a pulsed Nd:YAG laser with a wavelength of 1069 nm and delivering a maximum average power of 500 W. The laser beam was coupled to an optical fiber of 400 m core diameter and focused onto the upper surface of the target by means of 125 mm of focal length lens, where the spot diameter at normal incidence for a pulsed laser was about 0.20 mm. Other parameters were varied as fol- lows: laser pulse width 1–2 ms, frequency = 10 Hz, and pulse energy 2–8 J. The second laser source system was a CW monomode Ytter- bium doped fiber laser (YDFL), with a maximum average power of 200 W and wavelength of 1075 nm. The delivered irradiance ranged between 2 × 10 5 and 10 6 W/cm 2 . The laser beam was cou- pled to an optical fiber of 50 m core diameter and focused on the upper surface of the target by means of by means of 125 mm of focal length lens. The laser beam was kept in relative movement with respect to the metallic plate at a scanning speed of 5 mm/s. After each experiment with both lasers, the obtained colloidal 0169-4332/$ – see front matter © 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2014.01.083