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E. Bemporad , M. Sebastiani, F. Carassiti

E. Bemporad , M. Sebastiani, F. Carassiti University "Roma Tre", Dep't of Mechanical and Industrial Engineering Via Vasca Navale 79 - 00146 Rome Italy e.bemporad@stm.uniroma3.it. High resolution morphological and mechanical characterization of Niobium films obtained by MS and Biased MS PVD.

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E. Bemporad , M. Sebastiani, F. Carassiti

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  1. E. Bemporad, M. Sebastiani, F. Carassiti University "Roma Tre", Dep't of Mechanical and Industrial EngineeringVia Vasca Navale 79 - 00146 Rome Italy e.bemporad@stm.uniroma3.it High resolution morphological and mechanical characterization of Niobium films obtained by MS and Biased MS PVD The International Workshop on: Thin Films and new ideas for pushing the limits of RF superconductivity October 9-12, 2006

  2. Rome Where is the University “Roma Tre”? Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  3. Roma Tre, some numbers… • Born in 1992. • One of the 4 State University in Rome (9 in total). • 125.000 m2. • More than 40.000 students (3.900 enrolled in Engineering) • More than 700 Researchers and Professors. • Faculty of Engineering: • Civil • Computer Science • Electronic • Mechanical • Materials Science and Technology research group www.uniroma3.it Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  4. Main objectives of presented work • To measure basic surface mechanical properties of Nb films, such as hardness, Elastic modulus and work hardening behaviour; • To correlate this data with microstructure and surface roughness, which greatly affect the transition temperature (Tc) and the Residual Resistivity Ratio (RRR) of Nb films. • To compare results obtained from biased MS and non biased MS films Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  5. Outline • Introduction • Materials and methods • Modelling of basic surface mechanical properties overview • Results • Mechanical properties • Microstructure and morphology • Discussion and conclusions • Further developments Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  6. Introduction • Both structure and properties of films depend on deposition conditions used • Increasing bias voltage increases the energy of bombardment ions, resulting in: • Densification of the film • Increasing inherent compressive stress due to Ar incorporation • Additional defects in coatings structure • Changing in texture • Preferential grow direction Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  7. Introduction • Microstructural changes reflect also in mechanical properties changes • By the measure of mechanical properties the effect of deposition condition on microstructure can be verified Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  8. Materials and Methods Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  9. Materials Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  10. Materials Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  11. Methods • OM and SEM observation, plan view and LN2 cross-section • Micro Hardness measurements, both Vickers and Knoop indenters, with loads ranging from 1N down to 0,005N • AFM in contact mode on the surface and inside indentation marks • FIB-CrossBeam cross-section on the surface and inside indentation marks (still ongoing) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  12. Methods • Elastic modulus obtained by 3D reconstruction of residual indent volume and applying Lesage (on Vickers indent) and Marshall (on Knoop indents) models. • Work hardening behavior evaluated by the Indentation Size Effect (Meyer model); • Intrinsic hardness obtained applying Jonsson-Hogmark and Chicot-Lesage hardness models; Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  13. Modeling of basic surface mechanical properties Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  14. Vickers indenter Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  15. Knoop indenter Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  16. Vickers indentation at different loads Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  17. Elastic modulus, Lesage model Indentation performed at low load (0,005N), so to have z < film thickness/10 Model based on residual indent volume (VRe) measurement, and comparison with the theoretical one. Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  18. Elastic modulus, Lesage model J.Lesage et al., Surface and Coating Technology 81 (1996) 269-274 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  19. Elastic modulus, Marshall model D.B.Marshall, comunication of the American Ceramic Society, C-175 (1982) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  20. Vickers hardness Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  21. φ θ Knoop hardness L = 7,114w Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  22. σ σ n σS σS ε ISE – Meyer, elasto-plastic behaviour ε High load, macro hardness Low or very low load, micro/nano hardness Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  23. Lower loads ISE – Meyer, elasto-plastic behaviour Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  24. Lower loads Work hardening effect ISE – Meyer, elasto-plastic behaviour Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  25. ISE – Meyer, elasto-plastic behaviour Example: Ti6Al4V alloy Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  26. Film HV Substrate Hardness of the film Low Load Models Film Hardness of the substrate Substrate 1/d High Load Hardness of coated systems Plastic zone Plastic zone Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  27. Hardness of coated systems Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  28. Geometrical representation AF x x AS B B’ C’ C t t HF HF 11° 22° t t A A’ Total area : HS HS Brittle material Ductile material C=0.5 C=1 JÖNSSON & HOGMARK (1984) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  29. Chicot & Lesage (1995) + Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  30. Static and dynamic indentation • All model presented are based on measurements performed on the residual indent. • Some equipments, called depth sensing indenter, let to measure the load displacement curve during the indentation test • In this case the Oliver and Pharr method gives a way to evaluate hardness and Elastic modulus simultaneously, for a given maximum load • No data on depth sensing indentation will be reported in this work Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  31. Results Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  32. MHV at 0,5 g load Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  33. Elastic modulus and ISE unbiased MS E = 54,33 GPa Biased MS E = 88,95 GPa Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  34. Hardness comparison unbiased MS (#12-766) biased MS (#YY-767) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  35. Hardness comparison Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  36. Results Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  37. Results • Biased MS films show more than 50% higher MHV hardness then unbiased MS films • Biased films are more prone to be work hardened with respect to unbiased films • Elastic modulus of biased MS films resulted to be more than 60% higher than unbiased MS films • Such differences in Elastic Modulus are obviously not due to changes in the Nb Elastic properties, but due to a variation of coating microstructure (density, homogeneity, grain growth direction,…). Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  38. Micro morphology Cu substrate unbiased MS biased MS Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  39. Microstructure and morphology Ln2 cross section, biased MS, #R-768 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  40. Microstructure and morphology FIB cross section, unbiased MS, #2-770 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  41. Microstructure and morphology FIB cross section, unbiased MS, #2-770 Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  42. Results Halbritter, Journal Of Applied Physics 97, 083904 (April, 2005) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  43. Sub-micro morphology unbiased MS (#12-766); grain size ≈ 300nm biased MS (#R-768); grain size < 100nm Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  44. Sub-micro morphology unbiased MS (#12-766); grain size ≈ 300nm Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  45. Surface defects: FIB (25 kV, 8.000 x, SEMSE detector) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  46. Microdroplets Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  47. Sub-micro morphology biased MS (#R-768); grain size < 100nm Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  48. Sub-micro morphology G. Wu et al. / Thin Solid Films 489 (2005) 56– 62 51V bias Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  49. Ion beam sputtering on deposited film J. Appl. Phys., Vol. 81, No. 10, 15 May 1997 • Grain type A:channeling direction aligned with ion beam promote growing • Grain type B:shadowed by type A grain growing, demote growing • Grain type C:high ion sputter rate highly demote growing Roughness is proportional to normalized energy and film thickness Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

  50. Ion beam sputtering on deposited film biased MS (#Q-771) Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD

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