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Sebastiani - Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
 

Sebastiani - Nano-mechanical and microstructural characterization of MS-PVD Nb thin films

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Nano-mechanical and microstructural characterization of MS-PVD Nb thin films (Marco Sebastiani - 30')
Speaker: Marco Sebastiani - Roma 3 University | Duration: 30 min.
Abstract
E. Bemporad1, M. Sebastiani1, F. Carassiti1

1Mechanical and Industrial Engineering Department, University of Rome ‘Roma Tre’, Via della Vasca Navale 79-00146 Rome, Italy


The main objective of the present study was to identify the influence of the applied bias voltage on the microstructural and mechanical properties of magnetron sputtering physical vapour deposition (MS-PVD) niobium thin films for use in superconducting resonant cavities for particle accelerators.
The microstructure and mechanical properties evolution as a function of the applied bias voltage and nature of the substrate (copper or quartz) were investigated by means of micro-hardness and nanoindentation testing, FIB/SEM, AFM and TEM techniques.
The superconducting properties (critical temperature Tc and residual resistivity) were determined by a calibrated four-contact probe and a cryogenic apparatus and then correlated to the mechanical properties.
Significant difference in terms of microstructure, surface roughness and mechanical properties were observed for biased coatings grown on different substrates. The observed differences are likely connected to the low conductivity of quartz that induces a re-sputtering effect and a consequent modification of the superconducting performances.

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    Sebastiani - Nano-mechanical and microstructural characterization of MS-PVD Nb thin films Sebastiani - Nano-mechanical and microstructural characterization of MS-PVD Nb thin films Presentation Transcript

    • Material Science and Technology Research Group (STM)
      DipartimentodiIngegneriaMeccanica e Industriale
      Università Roma TRE
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Edoardo Bemporad, Marco Sebastiani, Fabio CarassitiGiulia Lanza and Enzo Palmieri
      The fourth international Workshop on:
      THIN FILMS AND NEW IDEAS FOR PUSHING THE LIMITS OF RF SUPERCONDUCTIVITY
      October 4-6, 2010
      Legnaro National Laboratories (Padua) ITALY
    • www.stm.uniroma3.it
      STM Roma TRE channel on YouTube
      Image Gallery
      Agilent Web seminar
      Interviews and videos on daily life at STM group
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      2
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • www.lime.uniroma3.it
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      3
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Resonant Cavities for particle accelerators
      NiobiumCoated (PVD)Coppercavity
      Bulk Niobium
      Very low Surfaceelectricalresistance
      (n a 1,8 K)
      Lowercosts
      Higherthermalstability
      But…
      Significantlylowersuperconductingperformances–WHY??
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      4
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Introduction
      5
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Many microstructural and morphological factors can affect the in-service performance of Nb coated OFHC Cu cavities (apart from impurities):
      • Roughness of the substrate;
      • Morphology of coating/substrate interface;
      • Coating thickness and thickness homogeneity;
      • Coating density
      • Grain size and crystals growth angle;
      • Thickness and composition of the surface oxide layer
      • Residual stress
      • All these aspects are related to the deposition parameters;
      1999, Physica C 316 153–88
      2005, Thin Solid Films 489 56–62
      1997 , J. Appl. Phys. 81 (10) 6754
      1998, Appl. Surf. Sci. 126 219–30
      2005, J. Appl. Phys. 97 083904
      2006, Physica C 441 79–82
    • Introduction
      Quality control measurement (RRR and Tc) are usually performed on Nb film deposited on Quartz substrate
      RRR and Tc measured on Quartz are very useful as threshold parameters;
      Nevertheless, characterization methods are absolutely necessary to verify what are the micro-structural differences between coatings which are grown either on quartz or on copper
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      6
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Supercond. Sci. Technol. (21 (2008) 125026)
    • Gap ofknowledge
      7
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      A comprehensive chemical, morphological, and mechanical surface characterization can be useful, in order to find out the appropriate correlation function among process parameters/microstructure/surface properties and superconducting properties
      In particular, the influence of the applied bias voltage on the functional and nano-mechanical properties of sputtered Nb thin films still needs to be deeply investigated.
      Supercond. Sci. Technol. (21 (2008) 125026)
    • Aimof the work
      8
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      To verify the influence of the applied bias voltage and nature of the substrate on the microstructural and nano-mechanical properties of MS-PVD Niobium thin films for use in superconducting resonant cavities for particle accelerators;
      To establish a correlation between the functional performance (RRR and Tc) and the observed microstructural/mechanical properties;
      To verify how nano-mechanical characterization can help in the characterization and quality control of such coatings
      Supercond. Sci. Technol. (21 (2008) 125026)
    • Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      9
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Hardness – Scale of indentation
      10 N
      10 mN
      Load
      Nano-hardness
      Micro-hardness
      Macro-hardness
      10
    • Roma TRE nanohardness tester
      Berkovichtip
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      11
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      early 2008
      - CSM option
      - Lateral force measurement
      - Nano- positioninng stage
    • Instrumented Indentation Testing
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      12
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • F
      F
      F
      h
      h
      h
      Depth Sensing Indentation describe materials behaviour: Elastic to Plastic Deformation
      Plastic
      Elastic - Plastic
      Elastic
      Stress-Strain
      curves
      Indentation
      curves
      Indentation
      prints
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      13
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Quasi-static Instrumented Indentation Testing
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      14
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Nano hardness maps
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      15
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Stiffness is determined NOT from the unloading curve, but continuously from the ratio of the amplitude of the imposed force oscillation (F0) to the amplitude of the resulting displacement oscillation (z0)
      Continuous stiffness measurement (CSM): in depth H and E variation, viscoelasticity
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      16
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Nanoindentation with CSM
      W. C. Oliver, G. M. Pharr, J. Mater. Res., Vol. 19, No. 1, Jan 2004
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      17
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • 80 nm thin ALD coating TiO2-Al2O3 coating on silver substrate (Roma Tre).
      CSM: analysis of thin coatings
      Pt
      TiO2
      Al2O3
      Intrinsic hardness of the top layer
      Silver
      TEM, 120kV, 380.000x dual-layer coating
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      18
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Tip rounding
      Surface roughness and chemistry
      Thermal Drift
      Initial penetration depth
      Instrument compliance
      Indenter geometry
      Specimen preparation and mounting
      Piling-up / sinking-in
      Substrate effect
      Indentation size effect
      Residual stress
      Factors affecting results
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      19
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Nano indentation: what’s really happened?
      • The correct understanding of microstructural effects during nanoindentation is not straightforward;
      • How to separate real microstructural effects from artifacts?
      • How to identify the actual deformation/failure mechanisms?
      • Must validate nanoindentation measurements
      • materials behavior during indentation would not be considered with just continuum theory
      • The solution relies in the coupled and synergic use of high resolution microscopy techniques and indentation testing
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      20
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      21
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Lime Lab: DualBeam (FEI) Helios 600 Nanolab
      early 2008
      - Omnprobe
      - GIS (4 gases)
      - STEM
      - EDS (Oxford)
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      22
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      23
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • DualBeam (FEI)
      SEM Column: spatial resolution 0,69 nm @ 15 kVFIB Column: spatial resolution5 nm @ 30 kV
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      24
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • High resolution electron column
      0,69 nmresolution, up to more that 1 million X
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      25
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Ion-Sample interaction
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      26
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Principal FIB modes:
      Deposition
      Imaging
      Milling
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      27
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • FIB modes: Ion imaging
      • Voltage contrast: insulators
      appear dark while grounded
      conductors are bright.
      • Materials contrast: differences
      in yield of secondary particles
      due to the way energy is lost
      in the material.
      • Crystallographic orientation
      contrast (channeling contrast):
      incident ions are channeled
      down between lattice planes
      of the specimen.
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      28
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Principal FIB modes:
      Deposition
      Imaging
      Milling
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      29
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • FIB modes: Ion Milling
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      30
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Principal FIB modes:
      Deposition
      Imaging
      Milling
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      31
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • FIB modes: Deposition (Pt)
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      32
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Possibility to reveal microstructure beneath the surface with very little or practically no artifacts
      Accurately localize the region of interest(within few nanometers)
      Excellent technique even on soft materials
      Time to produce a TEM lamella (couple of hours)
      EDS and Scanning Transmission Imaging within the DualBeam also available
      Using a DualBeam to characterize samples; what is new with respect to conventional characterization route?
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      33
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Cross sections
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      34
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • TEM lamella preparation
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      35
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • 36
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Resultsofexperimentalactivities and discussion
    • Depositionofcoatings
      37
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Fourdifferentcoatings are produced, byvarying the appliedbiasvoltage and the nature of the substrate.
    • Nanoindentation: howtoget the right numbers?
      38
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      1000 nm
      500 nm
      200 nm
      100 nm
    • Nanoindentation: howtoget the right numbers?
      39
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      1000 nm
      500 nm
      200 nm
      100 nm
    • Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Nanoindentation (CSM) on Nbthinfilms
      • Hardness data are notaffectedby the substrateonlyfor a penetrationdepth < t/10
      500 nm
      Substrate Influence on measured Hardness
      Substrate effects!!
      40
    • Nanoindentation: surfaceeffects
      41
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      Inaccuracies on hardness and modulus at indentation depths lower than 30 nm, due to roughness and tip rounding effects
      Elastic modulus at 25 nm:
      93,2 ± 35,82GPa
      Elastic modulus at 100 nm:
      106,21 ± 13,35GPa
    • Nanoindentation: deformationmechanisms
      Ptdeposition and FIB sectioning
      500 nm
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      42
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Partial re-crystallization during plastic deformation;
      • Relative sliding of columnar grain
      • Direct measurement of piling-up
      • Analysis of deformation mechanisms
    • Nanoindentation: deformationmechanisms
      200 nm
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      43
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Piling-up is still visible, but it is less pronounced
      • No more evidence of columns sliding and bending
      • Platic deformation is only given by dislocation nucleation and multiplication inside the grains.
    • Nanoindentation resultssummary
      44
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Deformationmechanisms at high loads
      45
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Strong pile-up at high indentationloads (> 1N)
      Vickers 1 N
    • Deformationmechanisms at high loads
      46
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Very low plastic deformation of the substrate
      • Lateral plastic flow, with strong column bending
      • Complete re-crystallization due to plastic deformation at the top of piled-up material
    • Micro-hardness on soft-on-hardsystems
      47
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Fitting of models for extracting properties from MICRO-hardness testing is not straightforward in this case due to the observed deformation mechanisms;
    • Coatings on Copper substrate
      BIASED (a-b)
      and
      UNBIASED (CERN, c-d) typecoatings on COPPERsubstrate
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      48
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Coatings on Copper substrate
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      49
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • BIASED (a-b)
      and
      • UNBIASED (CERN, c-d) typecoatings on QUARTZsubstrate
    • Nanoindentation: oxidelayer
      50
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • Indenter pop-in systematically observed at depth ~ 10 nm
    • TEM analysisof the oxidelayer
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      51
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      • The control of surface oxide layer can be very important in determining the functional performances of Nb coatings for superconducting applications
    • INFN Workshop, 10-2006
      Bemporad et al.: High resolution morphological and mechanical characterization of niobium films obtained by MS and Bias-MS PVD
      52
      Results
      Halbritter, Journal Of Applied Physics 97, 083904 (April, 2005)
    • FIB-SEM microstructural analysis
      An improper preparation of the copper substrate (usually electro-polishing + chemical polishing) dramatically decrease the interface and film quality, and the surface smoothness
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      53
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Correlationtosuperconductingperformances
      54
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      A difference in terms of Tc is observed between biased and unbiased films on quartz;
      This suggest a microstructural and morphological difference (density, grain size, lattice distortion, residual stress)
      Should we expect the same differences in terms of Tcalso for coatings on Copper?
    • Discussion: whataboutresidual stress?
      55
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      A difference in residual stress is expected both in case of different substrate and in case of applied bias voltage:
      Residual stress can reduce the elastic strain to failure, thus enhancing the possibility of defect formation (dislocations, delamination, micro-cracking and debonding of grains)
      Residual stress arises from a lattice distortion, thus influencing the electron-phonon coupling constant and the superconducting performance.
    • Conclusions
      Nano-mechanical testing can be a valuable procedure for the assessment of basic quality indicators for Nb films on either Copper or Quartz;
      Careful analysis of the raw data coming from nanoindentation allows to find out several important information:
      Actual elastic modulus and hardness of the coatings, leading to more reliable comparisons between samples;
      Presence of a thin oxide layer
      Surface and substrate effects
      Indirect evaluation of coating density
      A correlation is found between surface micro-roughness, coating density, mechanical properties and superconducting performance;
      The coupled use of HR microscopy techniques and hardness testing has been the key point of all research activities
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      56
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • FUTURE ACTIVITIES: FIB-DIC methodformeasuring stress GRADIENTS in coatings
      57
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
      DIC
      FEM
      Dual Beam FIB/SEM
      • Lateral resolution: <1um;
      • Depth resolution: <100 nm
      • Semi-automated procedure
      • This is an example of a PVD Gold film on Silicon…
      • Stress gradient analysis in Niobium films is still an unexplored field…PLEASE SEND US SAMPLES!!!
    • Thank you for yourtime and attention !
      marco.sebastiani@stm.uniroma3.it
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      58
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • 59
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • The starting point of the work here presented are the results published in a recent paper on Supercond. Sci. Technol. (21 (2008) 125026):
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      60
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Dynamic characterization of polymers in the time and frequency domains using a flat punch
      Highly plasticized polyvinylchloride,
      the complex modulus at 22 oC
    • Supeconducting properties of MS-PVD Nb films are significantly affected by
      Grain size
      surface roughness
      coating density
      interfaces integrity
      A completely different behaviour is expected for the BIASED Nb coating deposited on Quartz substrate
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      62
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • MTS Nano Event
      Roma TRE, April 3/04/2008
      M. Sebastiani: Applications of nanoindentation techniques to non-homogeneous materials and structures
      63
      Film
      Hsubstrate
      Hfilm
      Hardness
      Hardness
      Substrate
      Hfilm
      Hsubstrate
      1
      2
      1
      Indentation Depth/Film Thickness
      Indentation Depth/Film Thickness
      Surface Layers - Thin Film Effects
      Soft film on hard substrate
      Hard film on soft substrate
      Film
      Substrate
    • Ap
      h
      Apand Tip Calibration
      Perfect pyramid or cone:
      (C0 constant, 24.5 for Vickers)
      Perfect tip shape do not exist in the reality (tip blunting)
      Perfect tip Real tip
      Tip Calibration
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      64
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010
    • Hard inclusion in a soft metal
      Nano-mechanical and microstructural characterization of MS-PVD Nb thin films
      65
      Marco Sebastiani,
      Legnaro National Laboratories October 4 2010