Dr Sohaib Zia Khan received B.Eng degree (2001) in mechanical engineering from NED University, Pakistan, M.Sc degree (2006) in precision engineer and PhD degree (2010) for work on nanoparticles & CW laser ablation from University of Manchester, UK. Currently, he is an assistant professor at PNEC, National University of Sciences & Technology, Pakistan.
Abstract: Laser ablation in liquid is becoming an important technique for the generation of nanoparticles (NPs). Until now only pulsed lasers have been used; this is a pioneer work, using high-power, high-brightness continuous-wave (CW) fibre laser ablation in liquid, for the generation of NPs. A mechanism is proposed based on experimental observations, including high-speed imaging and emission spectroscopic analysis of the ablated plume. Three different target materials (Titanium, Nickel and Alpha-aluminium-oxide), submerged in either water or sodium dodecyl sulphate (SDS) solution at various concentrations were used. The characterisation of the generated metal-oxide NPs, in terms of size, size-distribution, shape, chemical composition and phase structure was carried out by UV-Vis photo-spectroscopy, transmission electron microscopy (TEM), high-resolution TEM with energy-dispersive X-rays spectroscopy and X-ray diffraction. This study paves a route towards a new application of CW fibre lasers. The book is useful to engineering students, professional engineers, researchers, academicians and scientists in materials, NPs characterisation, mechanical, laser processing and related disciplines.
Abstract: Laser ablation in liquid is one of the most widely investigated methods for generating various nanoparticles (NPs) that are difficult to produce using other means. In this paper, we report the generation of Al-oxide NPs by continuous-wave (CW) fibre laser ablation of corundum (α-Al2O3) target submerged in deionised water. The effects of CW fibre laser power and radiation time have been investigated. Characterisation of the NPs generated, in terms of size, size distribution, shape, chemical composition, and phase structure, was carried out by means of high-resolution transmission electron microscopy (HR-TEM), high angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results show that the average size of Al-oxide NPs, in the range of 17 to 29 nm, increased with increasing the laser power and laser exposure time, and the NPs are dominated by stoichiometric γ-Al2O3 with a minor phase of α-Al2O3. The mechanism involved in the CWLAL is also discussed.
Abstract: In recent years, laser ablation in liquid has become an increasingly important technique for the fabrication of nanoparticles (NPs). To date, only pulsed lasers have been used. This paper reports our recent studies on the generation of Ti-oxide and Ni-oxide NPs by the ablation of metal targets in aqueous environments using a high-power, high-brightness continuous-wave (cw) fibre laser at a wavelength of 1070 nm. Owing to the high and uniform irradiation, the fibre laser provides an alternative approach for NP generation with well-controlled phase, size and size distribution, along with high production rate. Characterization of the NPs, in terms of morphology, size and size distribution, chemical composition and phase structure, by means of high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD), has been presented. In addition, limitations of the cw fibre laser process have been discussed in comparison with pulsed laser process.
Abstract: Pulsed laser ablation in liquid (PLAL) has been widely applied for the generation of nanoparticles (NPs). We report on the generation of NiO NPs using a high-power, high-brightness continuous wave (CW) fiber laser source at a wavelength of 1,070 nm. Characterization of such NPs in terms of size distribution, shape, chemical composition, and phase structure was carried out by transmission electron microscopy (TEM), high-resolution TEM equipped with energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The results revealed the formation of NiO NPs in water with an average size of 12.6 nm. The addition of anionic surfactant sodium dodecyl sulfate (SDS) reduced the size of NiO NPs down to 10.4 nm. The shape of the NPs was also affected by the SDS, showing the change of shapes from spherical domination in water to tetragonal with increased SDS concentrations. Furthermore, the NiO NPs generated in water and SDS solutions were dual phase containing both cubic and rhombohedral structures. It was also found that the NiO NPs were single crystalline in nature irrespective of the size and shape.
Abstract: Previous studies on laser-assisted nanomaterial formation in liquids have focused on using pulsed laser ablation of metals. We report, for the first time to our knowledge, the fabrication of nanoparticles via high-power high-brightness continuous-wave fiber laser ablation of titanium in liquids. Analysis revealed the generation of spherical nanoparticles of titanium-oxide ranging mainly between 5 nm and 60 nm in diameter. A mechanism of formation for crystallized nanoparticles, based on the self-organized pulsations of the evaporated metal, is proposed. This may account for the observed substantial efficiency gain owing to the high average power and brightness of the source.
