Synthesis of gold colloids by laser ablation in thiol-alkane solutions
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Corrado Spinella IMM-CNR, 95100 Catania, Italy (Received 28 April 2004; accepted 26 July 2004)
In this paper, we present a study on the formation of gold colloids by laser ablation of a gold metal target in alkanes and thiol-alkane solutions. The results show a decrease of the gold particles’ size up to 2 nm when thiol molecules are present in the liquid environment. The observation of a blue-shift of the surface plasmon resonance is discussed together with transmission electron microscopy analyses accounting the cluster size decrease and the stabilization of the obtained suspensions. Formation of metal nanoparticles by laser ablation of solids in liquid environment has attracted much attention in the last few years.1–9 Indeed, this is an alternative way to well known chemical routes, and it is characterized by the absence of any counter-ion contamination or surface active substances.10,11 Recently, it has been shown that this method allows colloids to be obtained in several different liquid environments like water, ethanol, and various alkanes,12 increasing the possibility to use the obtained sols for practical purposes. Particularly interesting is the production of gold sols because gold nanoparticles can be used for many applications. They have been used as substrates for well-defined high-density polymer brushes obtained by surface initiated living radical polymerization,13 centers in networks,14 catalysts,15 and sensors.16 Moreover, gold clusters have stimulated new broad applications in bioscience, including their use as substrates for DNA attachment.17 Two problems are generally related to the formation of metal nanoparticles by laser ablation in liquids. The first concerns the generation of a broad cluster size distribution, with particles that rapidly coalesce due to postablation agglomeration. The second is observed at elevated laser fluences when the ejection of large fragments limits the rate of small cluster formation.6,9 In this respect, it has been recently demonstrated that the cluster size can be drastically reduced by the use of aqueous solution of surfactants, which cover the particles just after their ablation and thus prevent further agglomeration.18–20 In particular, Mafuné et al.1–3,18–20 showed that if sodium dodecyl sulfate (SDS) is used, the size distribution of gold, silver, and platinum particles thus
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0401 J. Mater. Res., Vol. 19, No. 10, Oct 2004
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produced shifts to a smaller value with an increase in surfactant concentration. However, this method is strongly limited to the water environment, and it is obtained with a two-phase system (micelle-water). We recently found the possibility of obtaining gold nanoparticles in a series of alkanes from pentane to decane, controlling their sizes and shapes as function of the ablation condition and the used alkane.21 In this paper, we report some data on the ablation in alkane-alkanethiol solut
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