Mohammed A. Al-Azawi

In situ measurement of gold nanoparticle production

Abstract. The closeness of the experimental and theoretical values enables the development of an in situ characterization technique to monitor and analyze the production of gold nanoparticles (NPs), overcoming the use of high-end and expensive instrumentation. Gold NPs below the radius size of 10 nm were successfully synthesized in accordance with a few working parameters of pulse laser ablation in a liquid technique. In this report, the size, shape, concentration, and aggregation properties of gold NPs were estimated by the Mie–Gans model based on a reliable and interactive real-time absorption spectroscopy. The major features can be an important means toward determination of efficient process measures, productivity of gold NPs generated, and efficiency of the mass ablation rate. The accuracy in the measurement is confirmed via transmission electron microscopy analysis.

Broadband optical absorption enhancement of N719 dye in ethanol by gold–silver alloy nanoparticles fabricated under laser ablation technique

Abstract. The formation of gold–silver alloy nanoparticles (Au–Ag alloy NPs) by a two-step process with a pulsed Nd:YAG laser without any additives is presented. Mixtures of Au and Ag colloidal suspensions were separately obtained by 1064-nm laser ablation of metallic targets immersed in ethanol. Subsequently, the as-mixed colloidal suspensions were reirradiated by laser-induced heating at the second-harmonic generation (532 nm) for different irradiation periods of time. The absorption spectra and morphology of the colloidal alloys were studied as a function of exposure time to laser irradiation. Transmission electron microscopy revealed the formation of monodispersed spherical nanoparticles with a homogeneous size distribution in all the synthesized samples. UV–vis and photoluminescence spectroscopy measurements were also employed to characterize the changes in the light absorption and emission of N719 dye solution with different concentrations of Au–Ag colloidal alloys, respectively. The localized surface plasmon resonance (LSPR) of Au–Ag alloy NPs enhanced the absorption and fluorescence peak of the dye solution. The mixture of dye molecules with a higher concentration of alloy NPs exhibited an additional coupling of dipole moments with the LSPR, thereby contributing to the improvement of the optical properties of the mixture.

Gold Nanoparticles Synthesized by Laser Ablation in Deionized Water

Gold nanoparticles were prepared by the pulsed laser ablation of high purity gold bulk immersed in deionised water. Pulses of a Q-switched Nd:YAG laser (fundamental wavelength, 1064 nm; laser fluence, 15 J/cm2; pulse duration, 8 ns) were employed to irradiate the gold surface during the ablation process. The effects of the thickness of the liquid layer and the post-ablative modification processes on ablation efficiency, size, and aggregation of gold nanoparticles were investigated. The experimental conditions that yielded the maximum ablation efficiency were determined. The average size and redistribution of nanoparticles were controlled by the subsequent treatment of the ablated colloid solution with a combination of 1064 and 532 nm pulses. The effects of post-ablation under laser-induced nanoparticles modification reduced the average particle size from 15.12 nm to 9.5 nm; the size distribution was also narrowed with 532 nm pulses. The results of UV-Vis spectrophotometer and transmission electron microscopy were exploited to characterize the optical spectra of gold colloidal solutions as well as to analyze the final shape and particle size distribution, respectively

The Effects of Liquid Environment on Ablation Efficiency and Morphology of Gold Nanoparticles Prepared by Laser Ablation Technique

Gold (Au) nanoparticles (NPs) were prepared by pulsed laser (Nd:YAG, 1064 nm) ablation of an individual target in deionized water (DIW), pure ethanol, and mixture of DIW and ethanol with different concentrations of ethanol. The effects of ambient liquid environment on ablation efficiency, stability, and size of Au NPs were experimentally investigated. The optical spectral characterization and morphological observations were determined by UV-Vis spectrophotometer and transmission electron microscopy, respectively. Particles are nearly spherical in shape in all liquid environments. The ablation experiment was initially performed by using DIW as the reference sample. The obtained Au NPs have an average particle size of about 18.71±7.50 nm. The comparison of the experimental results with the reference sample after a storage time of 48 h revealed that Au NPs in pure ethanol medium were not stable and exhibited much lower ablation efficiency and broader size distribution with an average particle size of 23.83±11.65 nm. Addition of ethanol with different volumes to the DIW significantly improved Au NPs properties in the mixture. The optimum ethanol concentration in the mixture was determined to be 70 vol%, which yielded the maximum ablation efficiency, rather narrow size distribution, and controllable size (12.43±8.10 nm) of Au NPs. A simple method for controlling the properties of Au NPs produced in the binary mixture of DIW-ethanol by laser ablation technique is presented.