Synthesis of Au/Si nanocomposite using laser ablation method

Highlights

• Laser ablation method is a strong tool to produce nanocomposite (Au/Si).

• Plasmonic absorption peak of Au nanoparticle makes energy transfer to the system.

• Morphology of nanocomposites is under the influence of their volumetric ratio.

• Size of nanostructures may be decreased by secondary laser irradiation.

• Oxygen bonds may be removed from oxide nanoparticles after laser irradiation.

Abstract

Production and characterization of gold/silicon nanocomposites have been investigated experimentally, using laser ablation method. Firstly Si nanoparticles and Au nanoparticles were synthesized by ablation of their bulk in deionized water with the fundamental wavelength of Nd:YAG pulsed laser separately. Then the produced Au nanoparticles and Si nanoparticles suspensions were mixed and irradiated with the second harmonic of the pulsed Nd:YAG laser operating at 532 nm. Effects of the volumetric ratio of Au and Si nanoparticle suspensions in the characteristics of Au/Si nanocomposite have been studied in this research. A variety of analytical techniques such as UV–Vis-NIR spectroscopy, X-ray diffraction, DLS measurement, FTIR spectrum, photoluminescence spectroscopy, and TEM and SEM imaging were applied to characterize the products. Strong plasmonic absorption band of Au nanoparticles around 530 nm made them to be heated and melted by the green laser irradiation to form nanocomposite with Si nanoparticles nearby.

Introduction

First studies on the nature of nanostructures were started since almost 50 years ago [1]. Experimental and theoretical investigations on this topic have leaded to valuable discoveries of the production of nanostructures and their potential in various applications of nanotechnology [2]. Nowadays, nanocomposites are employed in multiple technological fields such as electronics, optics, medical fields, material modifying and many other fields [3], [4], [5], [6], [7], [8]. Nanocomposites have gained much interest recently. Significant efforts are underway to control the nanostructures via innovative synthetic approaches [9], [10], [11], [12], [13], [14], [15], [16], [17]. Characteristics of nanocomposites are not only depends on its constituent materials but also to its size, structure and formation and it can exhibit different properties from its individual constituent materials and also its bulk form [18].

Coming to our subject, nanometer size noble metals such as gold and semiconductors such as silicon has vast usages in electronics and optics for their special properties [18], [19], [20], [21]. Nanocomposite structures containing both metals and semiconductors are expected to have important practical applications due to the fact that they exhibit surface plasmonic and excitonic resonance simultaneously [22], [23]. Thus nanocomposites of metal and semiconductors such as Au/Si have attracted significant interests due to their noticeable potential in the wide range of applications [24], [25].

According to Kleps and his co-worker’s report, Au nanoparticles on Si layer are greatly used in increasing substrate biocompatibility properties [26]. Derkacs et al. fabricated and characterized hydrogenated amorphous silicon thin film solar cells in which Au nanoparticles have been employed to engineer the transmission and spatial distribution of electromagnetic fields within the hydrogenated amorphous silicon layer [27]. Lin et al. fabricated a highly sensitive surface-enhanced Raman spectroscop substrate composed by ordered hexagonal-packed Si nanorod arrays joined with homogeneous Au nanoparticles [28]. Also Zhao et al. fabricated Au-Si nano-particle-decorated silicon nanowire arrays and their results showed that Au coating on the tip of silicon nanowires reduces the field emission properties of silicon nanowires because of Au having high work function [29]. Mohapatra et al. reported the formation of Au/Si coreshell nanoparticles embedded in silica matrix by atom beam cosputtering followed by annealing and their results showed that the formation of Si nanoshells around Au nanoparticles leads to the marked enhancement in the redshift and tunability of localized surface plasmon resonance (LSPR) [30]. In general it can be said that the composition of gold and silicon nanoparticles can improve the capability of individual nanoparticles in typical mentioned application.

Pulsed laser ablation (PLA) from a solid target in liquid medium is known as a physical technique for produced nanostructures. Among the advantages of PLA technique, we can mention the production of nanomaterials without impurities, the possibility of synthesis of various nanoscale materials by controlling the characteristics of ablation medium and also by adjusting different features of the used laser, such as its pulse width, wavelength and fluence [31], [32]. Many chemical and physical methods have been employed for fabricating nanocomposites. One of these methods is ablating a material in another nanomaterial solution [33]. Another method is that the mixture of nanostructures solution is irradiated by the laser pulse. The reason for using this method is that at least one of the nanostructures has an absorption peak around the laser wavelength [34]. In the case of nanoscale materials that have wide absorption peak in the UV region, suitable UV sources can be used to irradiate the nanostructures and compose them [18]. Use of ultrasonic waves is another method to compose nanostructures [35].

In this work we first synthesized the gold and silicon nanoparticles separately by pulsed laser ablation of their bulk in deionized water with 1064 nm wavelength of Nd:YAG pulsed laser. Then we mixed these nanoparticle suspensions in different volumetric ratio and irradiated the mixtures with the green beam of Nd:YAG laser (532 nm). The point is the strong plasmonic absorption of Au nanoparticles which occurs at about 532 nm wavelength [34]. This absorption heated and melted Au nanoparticles and made them to form nanocomposites with Si nanoparticles. The purpose of this work is introducing the laser irradiation method as a new and successfully way to synthesize Au/Si nanocomposite and to investigate the effect of different volumetric ratio of Au and Si nanoparticles colloidal suspensions on the characteristics of Au/Si nanocomposite.

This manuscript is organized as follow; following the introduction section, the experimental detail is described in Section 2. Section 3 is devoted to results and discussion and conclusion is presented in Section 4.