Production and characterization of Cu nanoparticles by pulsed laser ablation of solid Cu Target in Double Distilled Water PRESENTED BY DR.NISAR AHMAD, NIDA HARAM GC UNIVERSITY, LAHORE.
Introduction
Nanoparticle synthesis techniques Various methods using gas, liquid or solid phase processes: Flame pyrolysis, plasma and vapor phase synthesis Solution processing in which chemical reactions in solvents lead to the formation of colloids molecular self-assembly mechanical processes of size reduction including grinding, milling and alloying
Nanoparticle synthesis techniques Sythesis technique of our interest: Pulsed Laser Ablation of solid target in liquid environment Laser ablation has shown itself as one of the most efficient physical methods for nanofabrication To the best of our knowledge, we worked on this technique for the first time in Pakistan
Motivation for using this technique In the last decade, laser ablation in liquids has proven to be a unique and efficient technique with following advantages: 1. It can be applied universally with an almost unlimited variety of materials and solvents to generate nanoparticles. 2. No problems with the collection of the particles, compared with fabrication in gas. 3. Laser ablation yields principally cleaner particles, chemical precursors are not required and thus colloids are 100 percent pure.
4. Nanoparticle colloids are not inhalable and thus lead to an improved occupational safety. 5. Large number of available ablation parameters for controlling the size and shape of nanomaterials. 6. Produced nanomaterials have inherent stochiometry as their mother targets therefore, capability to produce nanomaterials of desired chemical composition.
Methodology The method consists of Ablation of of a target by an intense laser radiation in a liquid, yielding to an ejection of its constituents and to the formation of nanoclusters and nanostructures. Variety of liquids can be used in which the particles remain as a suspension. Up to today, about 20 different liquids have been used as the ablation media in particle fabrication ranging from organic solvents and water to liquid helium.
Effect of various parameters on the characteristics of nanoparticles Liquid Environment: When the ablation is performed in pure water or any other solution in the absence of chemically active components, the size of nanoparticles produced is relatively large. Various additives e.g. different salts such as NaCl, AgNO 3 and surfactants such as SDS and CTAB etc are applied to prevent agglomeration of the nanoparticles and increase the stability of the solution to control the particle size and size distribution.
Effect of various parameters on the characteristics of nanoparticles Laser irradiation parameters The range of size variation was rather moderate in the case of nanosecond pulses. More significant results were obtained by using ultrashort laser pulses. For nanosecond pulses, certain size control can be achieved by decreasing the wavelength of pumping radiation or decreasing the pulse width. The size properties can also be somewhat controlled by varying the laser fluence. At relatively low fluences, nanoparticles with relatively small mean size and narrow dispersion were obtained and vice versa. The fluence of laser irradiation has great influence on the shape formation of synthesized nanocrystals.
Experimental Schematics Convex lens Glass prism Nd : YAG Laser Laser beam DD water Teflon beaker Target
Experimental setup
Experimental specifications Laser: Nd :YAG laser, Q switched pulses; operating at fundamental wavelength(1064 nm) Pulse width: 7ns Repetition rate: 10 Hz Beam spot size: 2 mm Lens: Convex lens of focal length 50 cm Ablation time/ Number of pulses: 20 minutes/ 12000 pulses Liquid: 7cc Double distilled water Target: High purity Copper target of 1.5 mm thickness
Copper Metal oxide nanoparticles have shown great attention due to their tunable optical, electronic, magnetic and catalytic properties. Copper oxide is considered as an efficient catalytic agent and also a good gas sensing material.
Experiments Cu DDW 1 Energy: 0.132J, Fluence: 4.2 J/cm 2 Cu DDW 3 Energy: 0.18 J, Fluence: 5.73 J/cm 2 Cu DDW 4 Energy: 0.25 J, Fluence: 7.96 J/cm 2 Cu DDW 5 Energy: 0.312 J, Fluence:9.87 J/cm 2
Formation mechanism In general, copper is very reactive, and laser ablation of a copper metal target in water leads to the formation of copper oxide. Laser ablation produces high-temperature and high-pressure Cu plasma in the solid. Subsequent ultrasonic and adiabatic expansion of the high temperature and high-pressure Cu plasma results in cooling of the Cu plume region, and subsequent formation of Cu clusters. Once the plasma has been extinguished, the Cu clusters that have formed encounter the solvent, which induces chemical reactions to form Cu(OH)2 followed by the decomposition to produce copper oxides. At the same time, the Cu plasma causes water molecules to dissociate and supply O atoms. The Cu clusters in the water incorporate O atoms and become large particles through crystal growth. This crystal growth is accompanied by the oxidation reaction.[yamada et al.]
Characterizations Transmission Electron Microscopy(TEM) Carbon Coated TEM grids Deposition of colloidal solution of particles on grids Particle size and size distribution was carefully observed UV-Vis spectrophotometer 3cc sample in Quartz Cuvette Absorbance was checked for all the samples Used in spectrum mode
Characterizations Atomic Force Microscopy(AFM) Deposited on Glass Slides Particle size, shape, morphology, and distribution of particles PIXE Analysis Deposited on Transparency Purity of nanoparticles was checked
TEM Images of Cu nanoparticles At fluence 9.87J/cm 2 At fluence 4.2 J/cm 2
Overlay Absorbance Spectrum Wavelength (nm)
AFM images of Cu nanoparticles AFM 3D image of Cu nanoparticles at fluence 4.2 J/cm 2
Size distribution calculated by AFM images At Fluence 4.2J/cm 2 Particle frequency 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 particle frequency 50 45 40 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 Particle size(nm) 0 5 10 15 20 25 30 35 40 45 50 particle size(nm)
AFM 3D image of Cu nanoparticles at fluence 7.96 J/cm2
Size distribution calculated by AFM images At Fluence 7.96 J/cm 2 particle frequency 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 Particle Frequency 80 70 60 50 40 30 20 10 0 0 5 10 15 20 25 30 35 40 45 50 particle size(nm) Particle Size(nm)
Comparison of Particle Size and its distribution at Different Fluences Size distribution of nanoparticles at fluence 7.96 J/cm2 Size distribution of nanoparticles at Fluence 4.2 J/cm2 particle frequency 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 particle size(nm) Particle frequency 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 40 45 50 Particle size(nm)
PIXE analysis of Cu nanoparticles
Future prospects The independence of laser-based synthesis of dirty colloidal chemistry makes it unique for the fabrication of markers of bioanalytes for sensing and in vivo imaging applications. Among the noble metals, silver and gold due to its excellent biocompatibility raise considerable interest as nanoparticles for biomedical applications. Remarkable size-dependent optical properties of colloidal gold nanoparticles related to quantum size effects, and the antiviral/antimicrobial properties of silver make them very attractive for intensive research and their applications in nanobiotechnology.
Future prospects Quantum dots in Si, III-V and II-VI compounds e.g. ZnS, CdSe, GaAs etc needs increased fundamental Research and development (R&D) on the above-mentioned materials, as explained by the experts of MONA (European organization of merging optics and nanotechnologies) in a latest report.
Conclusion Laser ablation of a solid target in a liquid has been demonstrated to be an effective and general route to synthesize nanoparticles and nanostructures. A large variety of liquids and materials can be used for the required nanoparticle production with clean nanostructure synthesis in a well-controlled environment. Materials synthesized by laser ablation were found to exhibit unique properties and characteristics, which make them very important for many novel applications.
Acknowledgements We thank Dr. Irshad Hussain for helping us in coating the commercially available Copper TEM Grids.