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Structural and optical properties of pulsed laser deposited V2O5 thin films
Apr 20th, 2009
Thin film class Paper reading session
Presentation by Jiajia Tan
OutlineApplication of V2O5
Research Motivation and objective
Experimental procedure PLDCharacterization 1. XRD 2. XPS 3. Transmittance measurement 4. TEM
Important results
Conclusions
Application
Mainly:
Optical switching devices
Electrochromic devices
Cathodes materials for Li Battaries
Structure:
Orthorhombic unit cell
Layer-like structure
ObjectiveV2O5 thin films deposited by PLD
on amorphous glass
at 13.33 Pa and 220℃
at various laser fluence and pulse numbers.
MotivationVanadium oxide is a good catalyst,
especially when its size reaches nanoscale.
--->
The formation of nanoclusters.
Target:
1, Hhigh purity V2O3 powders are pressed to pallets;
2, V2O3 changes to V2O5 after annealed at 550 in air for 24℃ h.
Laser parameters:
*Pulsed ArF excimer laser (λ=193 nm,pulse duration 15 ns at FWHM)
at a fluence level of 0.9–2.7 J/cm2.
*Repetition rate was 2 Hz.
Experiment procedure: PLD
Experimental conditions
Important results
The size of NCs is in the range of 2–40 nm. From experimental results it is evident that NC size depends on the laser fluence used during deposition.
The optical band gap is about 2.52 eV.
Eghn )/1(^
T decreases at higher frequency.
Why?Quantum confinement effect give rise to the energy gap
Eg (film) = 2.52 eV > Eg (bulk) =2.25 eV.
In the range of 2–40 nm.
Conclusion
Structure:
Range from 2–40 nm.
NC size can be selected by adjusting the laser fluence.
Optical properties:
Aabsorption edge is about 2.52 eV.
Bohr radius is calculated to 4.52 nm.
Bohr radius:The physical properties change due to quantum confinement that results from electrons and holes being squeezed into a dimension that approaches a critical quantum measurement, called the exciton Bohr radius.