Density modulated nanoporous tungsten thin films and their nanomechanical properties


Density modulated tungsten (W) thin films with nanoscale porosity contents of 7% to 40% by volume were grown on Si substrates through magnetron sputter deposition. Process parameters were selected according to the structure zone model, which resulted in film thicknesses between 105 nm and 520 nm. Nanomechanical properties of samples were investigated by means of instrumented nanoindentation. Reduced-χ2 analysis was carried out to assess four models formulated through differential effective medium approach. The model that factored in both the crowding effect and the maximum random packing of pores successfully captured the experimental trends. Attempts to breach the auxetic barrier resulted in large-scale pulverization or spontaneous conversion into WO3. Porosity corrected yield strength calculations underlined the possibility of defining a porosity threshold beyond which the compressive yield strength of density modulated nanoporous metallic thin films would drop abruptly due to aggravated geometric slenderness effects in agreement with earlier hypotheses.

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  1. 1.

    J.P. Singh, T. Karabacak, D.X. Ye, D.L. Liu, R.C. Picu, T.M. Lu, and G.C. Wang: Physical properties of nanostructures grown by oblique angle deposition. J. Vac. Sci. Technol., B 23 (5), 2114 (2005).

    CAS  Article  Google Scholar 

  2. 2.

    J.A. Thornton: High rate thick film growth. Annu. Rev. Mater. Sci. 7, 239 (1977).

    CAS  Article  Google Scholar 

  3. 3.

    J.A. Thornton: The microstructure of sputter-deposited coatings. J. Vac. Sci. Technol., A 4 (6), 3059 (1986).

    CAS  Article  Google Scholar 

  4. 4.

    D.C. Meyer, A. Klingner, T. Holz, and P. Paufler: Self-organized structuring of W/C multilayers on Si substrate. Appl. Phys. A: Mater. Sci. Process. 69 (6), 657 (1999).

    CAS  Article  Google Scholar 

  5. 5.

    L.B. Freund and S. Suresh: Thin Film Materials: Stress, Defect Formation and Surface Evolution, 1st ed. (Cambridge University Press, Cambridge, England, 2004); pp. 60–72.

    Google Scholar 

  6. 6.

    A.M. Haghiri-Gosnet, F.R. Ladan, C. Mayeux, H. Launois, and M.C. Joncour: Stress and microstructure in tungsten sputtered thin films. J. Vac. Sci. Technol., A 7 (4), 2663 (1989).

    CAS  Article  Google Scholar 

  7. 7.

    H. Windischmann: Intrinsic stress in sputtered thin films. J. Vac. Sci. Technol., A 9 (4), 2431 (1991).

    Article  Google Scholar 

  8. 8.

    A.M. Haghiri-Gosnet, F.R. Ladan, C. Mayeux, and H. Launois: Stresses in sputtered tungsten thin films. Appl. Surf. Sci. 38 (1–4), 295 (1989).

    CAS  Article  Google Scholar 

  9. 9.

    M. Yonezawa, T. Yamazaki, and T. Kikuta: Porosity Assessment of NiO sputtered film and NO2 sensing property. J. Vac. Soc. Jpn. 53 (3), 226 (2010).

    CAS  Article  Google Scholar 

  10. 10.

    D. Ren, Y. Zou, C.Y. Zhan, and N.K. Huang: Study on the porosity of TiO2 films prepared by using magnetron sputtering deposition. J. Korean Phys. Soc. 58 (4), 883 (2011).

    CAS  Article  Google Scholar 

  11. 11.

    R. Messier, A.P. Giri, and R.A. Roy: Revised structure zone model for thin film physical structure. J. Vac. Sci. Technol., A 2 (2), 500 (1984).

    CAS  Article  Google Scholar 

  12. 12.

    T. Karabacak, C.R. Picu, J.J. Senkevich, G.C. Wang, and T.M. Lu: Stress reduction in tungsten films using nanostructured compliant layers. J. Appl. Phys. 96 (10), 5740 (2004).

    CAS  Article  Google Scholar 

  13. 13.

    T. Karabacak, J.J. Senkevich, G.C. Wang, and T.M. Lu: Stress reduction in sputter deposited films using nanostructured compliant layers by high working-gas pressures. J. Vac. Sci. Technol., A 23 (4), 986 (2005).

    CAS  Article  Google Scholar 

  14. 14.

    J.W. Hutchinson: Mechanics of Thin Films and Multilayers: Course Notes (Technical University of Denmark, Technical Report, 1996).

  15. 15.

    M. Ohring: Materials Science of Thin Films, 2nd ed. (Academic Press, San Diego, CA, 2002); pp. 641–742.

    Google Scholar 

  16. 16.

    A.G. Evans and J.W. Hutchinson: The thermomechanical integrity of thin films and multilayers. Acta Metall. Mater. 43, 2507 (1995).

    CAS  Article  Google Scholar 

  17. 17.

    I. Petrov, P. Barna, L. Hultman, and J. Greene: Microstructural evolution during film growth. J. Vac. Sci. Technol., A 21, S117 (2003).

    CAS  Article  Google Scholar 

  18. 18.

    D.L. Smith: Thin-Film Deposition: Principles and Practice, 1st ed. (McGraw-Hill Professional, New York, NY, 1995); pp. 307–318.

    Google Scholar 

  19. 19.

    T. Karabacak, Y.P. Zhao, G.C. Wang, and T.M. Lu: Growth front roughening in amorphous silicon films by sputtering. Phys. Rev. B 64 (8), 085323 (2001).

    Article  CAS  Google Scholar 

  20. 20.

    R. Liu and A. Antoniou: A relationship between the geometrical structure of a nanoporous metal foam and its modulus. Acta Mater. 61 (7), 2390 (2013).

    CAS  Article  Google Scholar 

  21. 21.

    C. Lu, X. Shun, and O. Lewis: Investigation of film-thickness determination by oscillating quartz resonators with large mass load. J. Appl. Phys. 43 (11), 4385 (1972).

    Article  Google Scholar 

  22. 22.

    M.T. Demirkan, L. Trahey, and T. Karabacak: Cycling performance of density modulated multilayer silicon thin film anodes in Li-ion batteries. J. Power Sources 273 (6), 52 (2015).

    CAS  Article  Google Scholar 

  23. 23.

    W.C. Oliver and G.M. Pharr: An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J. Mater. Res. 7 (4), 1564 (1992).

    CAS  Article  Google Scholar 

  24. 24.

    A.C. Fischer-Cripps: Nanoindentation, 3rd ed. (Springer, New York, NY, 2011); pp. 1–29.

    Google Scholar 

  25. 25.

    R. Pal: Porosity-dependence of effective mechanical properties of pore–solid composite materials. J. Compos. Mater. 39 (13), 1147 (2005).

    CAS  Article  Google Scholar 

  26. 26.

    A. Chatterjee, N. Kumar, J.R. Abelson, P. Bellon, and A.A. Polycarpou: Nanoscratch and nanofriction behavior of hafnium diboride thin films. Wear 265, 921 (2008).

    CAS  Article  Google Scholar 

  27. 27.

    P.C. Meier and R.E. Zund: Statistical Methods in Analytical Chemistry, 2nd ed. (John Wiley & Sons, New York, NY, 2000); p. 76.

    Google Scholar 

  28. 28.

    E. Lassner and W-D. Schubert: Tungsten: Properties, Chemistry, Technology of the Element, Alloys, and Chemical Compounds, 1st ed. (Kluwer Academic/Plenum Publishers, New York, NY, 1999); pp. 11–85.

    Google Scholar 

  29. 29.

    K.K. Shih, D.A. Smith, and J.R. Crow: Properties of hard tungsten films prepared by sputtering. J. Vac. Sci. Technol. A 6 (3), 1681 (1988).

    CAS  Article  Google Scholar 

  30. 30.

    J. Bernardini and D.L. Beke: Diffusion in nanomaterials. In Nanocrystallinen Metals and Oxides, 1st ed., P. Knauth and J. Schoonman eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2002; pp. 41–79.

    Google Scholar 

  31. 31.

    T. Ozkan, D. Shaddock, D.M. Lipkin, and I. Chasiotis: Mechanical strengthening, stiffening, and oxidation behavior of pentatwinned Cu nanowires at near ambient temperatures. Mater. Res. Express 1 (3), 035020–035021 (2014).

    Article  CAS  Google Scholar 

  32. 32.

    A. Warren, A. Nylund, and I. Olefjord: Oxidation of tungsten and tungsten carbide in dry and humid atmospheres. Int. J. Refract. Met. Hard Mater. 14, 345 (1996).

    CAS  Article  Google Scholar 

  33. 33.

    F. Huth, M. Schnell, J. Wittborn, N. Ocelic, and R. Hillenbrand: Infrared-spectroscopic nanoimaging with a thermal source. Nat. Mater. 10, 352 (2011).

    CAS  Article  Google Scholar 

  34. 34.

    C. Li, J.H. Hsieh, M-T. Hung, and B.Q. Huang: The deposition and microstructure of amorphous tungsten oxide films by sputtering. Vacuum 118, 125 (2015).

    CAS  Article  Google Scholar 

  35. 35.

    A.F. Bower: Applied Mechanics of Solids, 1st ed. (CRC Press, Boca Raton, FL, 2010); pp. 85–87.

    Google Scholar 

  36. 36.

    Y. Li and A. Antoniou: Synthesis of transversely isotropic nanoporous platinum. Scr. Mater. 66, 503 (2012).

    CAS  Article  Google Scholar 

  37. 37.

    M.O. Jensen and M.J. Brett: Porosity engineering in glancing angle deposition thin films. Appl. Phys. A 80 (4), 763 (2005).

    CAS  Article  Google Scholar 

  38. 38.

    Y. Ding and Z. Zhang: Nanoporous metals. In Springer Handbook of Nanomaterials, 1st ed., R. Vajtai ed.; Springer Science: New York, NY, 2013; pp. 799–802.

    Google Scholar 

  39. 39.

    L. Wang: Structural tailoring of nanoporous metals and study of their mechanical behavior (University of Kentucky Theses and Dissertations in Chemical and Materials Engineering, Louisville, KY, 2013); pp. 5–131.

    Google Scholar 

  40. 40.

    C. Ma, S.C. Wang, R.J.K. Wood, J. Zekonyte, Q. Luo, and F.C. Walsh: Hardness of porous nanocrystalline Co–Ni electrodeposits. Met. Mater. Int. 19 (6), 1187 (2013).

    CAS  Article  Google Scholar 

  41. 41.

    N. Huber, R.N. Viswanath, N. Mameka, J. Markmann, and J. Weissmuller: Scaling laws of nanoporous metals under uniaxial compression. Acta Mater. 67, 252 (2014).

    CAS  Article  Google Scholar 

  42. 42.

    K.L. Johnson: Contact Mechanics, 1st ed. (Cambridge University Press, Cambridge, England, 2001); pp. 171–179.

    Google Scholar 

  43. 43.

    K.M. Lee, C-D. Yeo, and A.A. Polycarpou: Relationship between scratch hardness and yield strength of elastic perfectly plastic materials using finite element analysis. J. Mater. Res. 23 (8), 2229 (2008).

    CAS  Article  Google Scholar 

  44. 44.

    A. Giri, J. Tao, M. Kirca, and A.C. To: Mechanics of nanoporous metals. In Handbook of Micromechanics and Nanomechanics, 1st ed., S. Li and X-L. Gao eds.; Pan Stanford Publishing: Singapore, Singapore, 2013; pp. 827–867.

    Google Scholar 

  45. 45.

    X-Y. Sun, G-K. Xu, X. Li, X-Q. Feng, and H. Gao: Mechanical properties and scaling laws of nanoporous gold. J. Appl. Phys. 113, 023505–1 (2013).

    Article  CAS  Google Scholar 

  46. 46.

    A.M. Hodge, J. Biener, J.R. Hayes, P.M. Bythrow, C.A. Volkert, and A.V. Hamza: Scaling equation for yield strength of nanoporous open-cell foams. Acta Mater. 55, 1343 (2007).

    CAS  Article  Google Scholar 

  47. 47.

    D. Lydzba and J.F. Shao: Modeling of plastic deformation of saturated porous materials: Effective stress concept. In Applied Micromechanics of Porous Materials, 1st ed., L. Dormieux and F-J. Ulmedited eds.; Springer: Udine, Italy, 2005; pp. 187–204.

    Google Scholar 

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Authors Tanil Ozkan and Andreas A. Polycarpou gratefully acknowledge the support of the National Science Foundation under grant no. NSF CMMI 1030657. Film growth and structural analyses of films were carried out in the laboratories of the University of Arkansas at Little Rock. Nanoindentation, SPM and AFM analyses were performed in the Frederick Seitz Materials Research Laboratory Central Research Facilities, University of Illinois. Authors gratefully acknowledge Dr. Tobias Gokus at Neaspec GmbH for nano-FTIR analysis. Authors also express their gratitude for the constructive feedback they received from the reviewers of the JMR, which enhanced the scope and the depth of analysis provided in the revised version of this paper.

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Ozkan, T., Demirkan, M.T., Walsh, K.A. et al. Density modulated nanoporous tungsten thin films and their nanomechanical properties. Journal of Materials Research 31, 2011–2024 (2016).

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