PRESENTED BY

DR.NISAR AHMAD, NIDA HARAM

GC UNIVERSITY, LAHORE.

Production and characterization of Cu nanoparticles by pulsed laser ablation of solid Cu Target in Double Distilled Water

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 controllingthe 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, AgNO3 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 parametersThe 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 thepulse 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

Nd : YAG Laser

Convex lens Glass prism

Laser beam

Teflon beaker

DD water

Target

Experimental setup

Experimental specifications

Laser:Nd :YAG laser, Q switched pulses; operating at fundamental wavelength(1064 nm)Pulse width: 7nsRepetition rate: 10 HzBeam 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 1Energy: 0.132J , Fluence: 4.2 J/cm2

Cu DDW 3Energy: 0.18 J , Fluence: 5.73 J/cm2

Cu DDW 4Energy: 0.25 J , Fluence: 7.96 J/cm2

Cu DDW 5Energy: 0.312 J , Fluence:9.87 J/cm2

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 clustersthat 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 spectrophotometer3cc 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 AnalysisDeposited on Transparency

Purity of nanoparticles was checked

TEM Images of Cu nanoparticles

At fluence 9.87J/cm2 At fluence 4.2 J/cm2

Overlay Absorbance Spectrum

Wavelength (nm)

AFM images of Cu nanoparticles

AFM 3D image of Cu nanoparticles at fluence 4.2 J/cm2

Size distribution calculated by AFM images

At Fluence 4.2J/cm2

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AFM 3D image of Cu nanoparticles at fluence 7.96 J/cm2

Size distribution calculated by AFM images

At Fluence 7.96 J/cm2

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Comparison of Particle Size and its distribution at Different Fluences

Size distribution of nanoparticles at fluence 7.96 J/cm2

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Size distribution of nanoparticles at Fluence 4.2 J/cm2

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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 nanoparticlesand 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.