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.