1. Thermodynamic stability of VO2 in contact with thin metal films
N F Thabezhe (University of Zululand)
Energy Postgraduate Conference 2013

2. Introduction
Vanadium Oxide compounds (VO2, V2O3, V2O5, V6O13 etc ) undergo a first order phase transition if their temperature is raised from below to above their transition temperature.
This transition is accompanied by variations in their electrical, magnetic and optical transmittance
VO2 has a transition temperature closer to room temperature

3. Introduction At room temperature it is a semiconductor
At higher temperature (~68C) changes to metallic state.
Changes from the low temperature monoclinic crystal structure to the high temperature tetragonal-type lattice

4. Experimental Procedure
VO2 thin films were deposited by means of an rf-inverted cylindrical magnetron sputtering system on chemically cleaned glass substrates
The metals (Co, Hf, Ni, Pd and Pt) were deposited on top of VO2 by means of an electron beam evaporator system (shown below) in vacuum of better than 4x10-8 kPa
Annealing was done in vacuum of better than 2x10-8 kPa for times ranging from 45 min to 1 h.

5. Results
RBS spectra of glass/VO2(4500 Å)/Hf(3650 Å) samples as-deposited and annealed for 45 min.

6. Results
X-ray diffraction spectra for samples with structure glass/VO2/Hf after being annealed for 45 minutes

7. Results
RBS spectra of samples with structure glass/VO2/Pt. RBS shows that there is no reaction between Pt and VO2 even after annealing the samples at 700 oC for 1 hour.

8. Results

9. Conclusion
No interfacial reactions could be detected between metals ( Co, Ni, Pd, Pt ) and VO2.
In the case of Hf on VO2 it was found a reaction occurs at about 400 oC producing HfV2 and HfO2.
In all cases investigated it was found that a reaction happens when the heat of reaction between the reactants is negative and none occurs when it is positive.
Metals with an electronegativity value of less than 4.9 V were found to react with VO2 while those with a value greater than 4.9 V do not react.

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