Structural and optical properties of pulsed laser deposited V 2 O 5 thin f ilms Apr 20 th, 2009 Thin film class Paper reading session Presentation by Jiajia Tan

Outline Application of V 2 O 5 Research Motivation and objective Experimental procedure PLD Characterization 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

Objective V 2 O 5 thin films deposited by PLD on amorphous glass at Pa and 220 ℃ at various laser fluence and pulse numbers. Motivation Vanadium oxide is a good catalyst, especially when its size reaches nanoscale. ---> The formation of nanoclusters.

Target: 1, Hhigh purity V 2 O 3 powders are pressed to pallets; 2, V 2 O 3 changes to V 2 O 5 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/cm 2. *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. 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.