Modern Applied Science; Vol. 9, No. 6; 2015 ISSN 1913-1844 E-ISSN 1913-1852 Published by Canadian Center of Science and Education 20 Effect of Liquid Layer Thickness on the Ablation Efficiency and the Size-Control of Silver Colloids Prepared by Pulsed Laser Ablation Mohammed A. Al-Azawi 1 , Noriah Bidin 2 , Abdulrahman K. Ali 3 , Khaleel I. Hassoon 3 & Mundzir Abdullah 1 1 Department of Physics, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Johor, Malaysia 2 Advance Photonic Science Institute, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Johor, Malaysia 3 Laser and Optoelectronics Branch, Department of Applied Sciences, University of Technology, Baghdad, Republic of Iraq Correspondence: Noriah Bidin, Advance Photonic Science Institute, Faculty of Science, Universiti Teknologi Malaysia, Johor Bahru, Johor, Malaysia. E-mail: noriah@utm.my/mohammed.a.alazawi@gmail.com Received: December 10, 2014 Accepted: December 24, 2014 Online Published: March 24, 2015 doi:10.5539/mas.v9n6p20 URL: http://dx.doi.org/10.5539/mas.v9n6p20 Abstract Sliver colloidal solutions were synthesized by Nd: YAG laser ablation 1064 nm of a high purity silver target immersed in deionised water. The effect of water layer thickness on the laser ablation efficiency of nanoparticles was investigated experimentally. UV-Vis spectrophotometer and transmission electron microscopy observations were employed to characterize the optical spectra and particle sizes of colloids, respectively. The optimum parameter of the water layer thickness (which yielded the maximum ablation efficiency) was determined. It was demonstrated that both: the average particle size and the ablation efficiency which can be tuned by choosing suitable experimental parameters of liquid layer thickness, laser fluence and post-ablation laser wavelength. Average particle size and redistribution of nanoparticles was controlled by the subsequent treatment of the ablated colloid solution with combination of 1064 and 532 nm pulses. The effects of post-ablation under laser-induced particle modification reduced the average particle size from 15.1 to 4.3 nm. Particle size distribution was also narrowed with 532 nm pulses. Keywords: laser ablation, silver nanoparticles, ablation efficiency, laser irradiation 1. Introduction Nanoparticles of noble metals are the essential structures of nanotechnology and have draw much attention from researchers due to their size dependent electronic, catalytic, magnetic, and optical properties (Desarkar et al., 2012; Hajiesmaeilbaigi et al., 2006). Almost, all physical properties of the materials change significantly as the size of the constituting particles reaches the nanoscale regime. These variations in properties result from the presence of a small number of atoms in each particle and a high surface-to-volume ratio, due to the large fraction of atoms that reside on the particle’s surface, as well as the electronic energy bands having control over the majority of the physical and chemical properties being drastically modified (Dorranian et al., 2013; Huang et al., 2009). The spacing of electronic levels and bandgap increases with the decreasing particle size. This is because the electron - hole pairs and the Columbic interaction between them are much closer together (Schmid, 1992; Zhang, 2003). With regards to the UV-Vis optical spectra silver colloidal; this increase in the bandgap can be observed experimentally via the blue-shift in the absorption spectrum. These size-dependent silver nanoparticle (Ag NPs) properties are exploited in many potential applications such as antibacterial activity (Das et al., 2011), solar energy conversion (Berginc et al., 2014), light-emitting devices (Qiao et al., 2013), chemical/biological sensors (Frederix et al., 2003; Joshi and Kruis, 2006), and photocatalysis (Linic et al., 2011). Silver nanoparticles have an advantage over other metal nanoparticles (e.g., gold and copper) since the Surface Plasmon Resonance (SPR) energy of Ag is located far from the inter band transition energy (Hajiesmaeilbaigi, et al., 2006). Therefore, the position of SPR peak for silver nanoparticles in water can be controlled over a range of 380 – 500 nm by changing the particle size to obtain a unique property. The successful establishment of this important part of nanotechnology depends first on the control of particle size, morphology, and the composition of metal nanoparticles during synthesis. Generally, metal NPs can be prepared by various physical and chemical