Nanoparticle Dynamics During Laser Synthesis of Zinc Oxide Nanocrystals

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Nanoparticle Dynamics During Laser Synthesis of
Zinc Oxide Nanocrystals

• By
• Lorenzo Smith
• Renato Camata (mentor)

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Motivation

• Zinc Oxide (ZnO) is a promising wide bangap
  semiconductor material
• Other important properties of ZnO
• piezoelectricity
• biocompatibility
• easy manufacturing of nanostructures

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Motivation

• Potential technological applications of ZnO
• UV light emitting devices and sensors
• transducers
• biosensors
• ZnO thin films and nanostructures can be grown on
  cheap substrates such as glass
• Understanding the synthesis and behavior of ZnO
  materials may enable the deployment of these new
  technologies.
• The combination of laser ablation and aerosol
  processes provides a good platform for ZnO
  nanostructure synthesis.

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Goal

• The goal of this project is to investigate the
  behavior of aerosol populations during the
  synthesis of ZnO nanocrystals by laser ablation.
  On-line measurements of the aerosol size
  distributions may help improve control over the
  synthesis of ZnO nanostructures.

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Schematic of the experimental setup for on-line
measurements of aerosol size distributions
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Reproducibility Test
Size distributions look like bell-shaped curves
(Gaussian ?)
Data Fluctuations of up to 30 detected. Must be
careful with data analysis.
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Log Curve Fitting to Measured Size Distribution
Size Distributions well represented by the
Log-Normal distribution function.
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Log-Normal Function
N Number of Particles
Dp Diameter of Particles
Dpg Average size of distribution
?g Standard Deviation
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Log-Normal Size Distributions
Examples of Log-Normal Distribution? stays the
same
N decreases
Dpg increases
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Effect of Laser Energy Density
?Higher number of particles
E 3 - 6 J/cm2 Higher energy density
?Larger average particle size
?Drop in number of particles
E gt 6.2 J/cm2 Higher energy density
?Lower average particle size
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Processes of Nanoparticle Growth
condensation/ coalescent coagulation
nucleation
vapor
formation of small aggregates
further growth by aggregation
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Results

• Nanoparticle populations exhibit lognormal size
  distributions with a concentration peak in the
  20-25 nm size range.
• As the laser energy density is raised the size
  of particles and their total concentration
  increases up to 6.25 J/cm2, at which a sudden
  drop occurs.

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Conclusion

• We have been able to monitor the aggregation
  process of these gas-suspended ZnO nanoparticles.
  
• This may allow better control of laser
  synthesized ZnO nanostructure films for potential
  integration into functional systems.

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ZnO Future

• There has been much interest in optoelectronics
  applications to use this material as a UV laser.
• Zinc Oxide is a strong candidate for
  short-wavelength optical devices such as light
  emitting diodes or laser diodes.
• Being considered for antireflection coatings, gas
  sensors, and photoluminescent devices

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Acknowledgement

• We acknowledge support from the National Science
  Foundation (NSF)-Research Experiences for
  Undergraduates (REU)-site award to the University
  of Alabama at Birmingham (UAB).

NANOMATERIALS LABORATORY
Thank You For the Opportunity