Fabrication of Vanadium Oxide Nanoparticles by Pulsed Laser Ablation
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Pulsed laser ablation in liquid (PLAL) is an eco-friendly nanoparticles fabrication technique. PLAL uses laser light to ablate a solid material which is submerged in a liquid medium. During the interaction of laser light with the solid target plasma will be formed. In the high pressure and temperature of the plasma, nanoparticles are formed. This thesis deals with PLAL for synthesis of vanadium oxide. Vanadium oxide refers to an inorganic compound with general formula of VnO2n+1. There are approximately 15-20 stable vanadium oxides. Out of these, eight oxides show reversible phase transition from a semi-conducting phase to a metallic phase at a critical temperature (Tc). The range of temperatures where the transition occurs is between -147℃ to 375℃. The Tc for most commonly used vanadium oxides are 68 ℃ (VO2), -105 ℃ (V2O3) and +375 ℃ (V2O5). The phase transition is accompanied by a change in crystal structure, optical and electrical properties. These temperature dependent changes have applications in optics and electronics. The aim of the thesis is to investigate possible methods to synthesis vanadium oxides by PLAL. Fabrication of less thermodynamically stable oxides (such as VO2, V2O3) demands careful control of the process parameters. Special attention is devoted for fabrication of VO2 because of its Tc is near to room temperature. It can be used for window coatings, opto-electronic memories, and switches. In the experiments, pure vanadium (99.8%) metal-target is ablated by a high repetition rate fiber laser in a liquid medium. The liquid has a significant influence on the reactivity and stability of the particles and great care was taken in the selection of liquid during the experiments. Different liquids such as acetone, ethanol, methanol, water, pyridine, acetonitrile, stabilizer Sodium Dodecyl Sulfate (SDS) and as oxidizing agent hydrogen peroxide are used. This thesis work has produced V2O5.nH2O gel and it was converted to VO2 by annealing in vacuum chamber. Fibers like nanoparticles of VOX were synthesized by PLAL in acetone-water mixture and acetonitrile-acidified water mixtures. Pure vanadium nanoparticles were produced in polar aprotic solvents (acetone, pyridine and acetonitrile). The synthesized products were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Optical Spectroscopy and Raman Spectrometry.