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Thermodynamic stability of VO2 in contact with thin metal films

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

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Thermodynamic stability of VO2 in contact with thin metal films

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  1. Thermodynamic stability of VO2in 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.

  10. References • [1] F. Guimeton, L. Sauoes, J.C. Valmelette, Thin Solid Films 446 (2004)287. • [2] J.B. Kana Kana, J.M. Ndjaka, P.Owono Ateba, B.D. Ngom, N. Manyala, O Nemraoui, A.C. Beye, and M. Maaza, Applied Surface Science 254(2008)3959-3963. • [3] B.S. Knight jr, R. Babb, M. Ray, T.J. Banisaulas III, L. Russon, R.S. Dailey, E.R. Davidson, J. Chem. Phys. 105(1996)10237. • [4] F.J. Morin, Phys. Rev. Lett. 3(1959)34. • [5] C.S. Blackman, C. Piccirillo, R. Binions, I.P. Parkin, Thin Solid Films – in press. • [6] L.A. Rayabova, I.A. Serbinov, A.S. Darensky, J. Electrochem. Sic. 119(1972)427. • [7] M.H. Lee, M.G. Kim, H.K. Song, Thin Solid Films, 291(1996)30. • [8] G.V. Jorgenson, J.C. Lee, Solar Energy Mater. 14(1986)205 • [9] T.B. Massalski (ed.). Binary Alloy Phase Diagrams, American Society for Metals, Metals Park, OH, 1st edn., 1986. • [10] R. Pretorius, J.M Harris, M.-A. Nicolet. Solid State Electron. 21(1978)667. • [11] O.M. Ndwandwe, Q.Y. Hlatshwayo, R. Pretorius, Mater. Chem & Phys. 92 (2005)487-491. • [12] F.R. de Boer, R. Boom, W.C.M. Mattens, A.R. Miedema, A.K. Niessen, • Cohesion in Metals, Transition Metal Alloys, Elsevier Science Publishers, • Amsterdam, The Netherlands, (1989). • [13] A.R. Miedema, P.F. de Châtel, F.R. de Boer. Physica, B 100, (1980) 1.

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