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Nanoparticle Dynamics During Laser Synthesis of Zinc Oxide Nanocrystals

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Title: Nanoparticle Dynamics During Laser Synthesis of Zinc Oxide Nanocrystals


1
Nanoparticle Dynamics During Laser Synthesis of
Zinc Oxide Nanocrystals
  • By
  • Lorenzo Smith
  • Renato Camata (mentor)

2
Motivation
  • Zinc Oxide (ZnO) is a promising wide bangap
    semiconductor material
  • Other important properties of ZnO
  • piezoelectricity
  • biocompatibility
  • easy manufacturing of nanostructures

3
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.

4
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.

5
Schematic of the experimental setup for on-line
measurements of aerosol size distributions
6
Reproducibility Test
Size distributions look like bell-shaped curves
(Gaussian ?)
Data Fluctuations of up to 30 detected. Must be
careful with data analysis.
7
Log Curve Fitting to Measured Size Distribution
Size Distributions well represented by the
Log-Normal distribution function.
8
Log-Normal Function
N Number of Particles
Dp Diameter of Particles
Dpg Average size of distribution
?g Standard Deviation
9
Log-Normal Size Distributions
Examples of Log-Normal Distribution? stays the
same
N decreases
Dpg increases
10
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
11
Processes of Nanoparticle Growth
condensation/ coalescent coagulation
nucleation
vapor
formation of small aggregates
further growth by aggregation
12
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.

13
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.

14
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

15
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
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