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Spradlin - Texture study of energetic condensed niobium thin films
 

Spradlin - Texture study of energetic condensed niobium thin films

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http://www.surfacetreatments.it/thinfilms ...

http://www.surfacetreatments.it/thinfilms

Texture Analysis of Niobium Thin Films (Josh Spradlin - 20')
Speaker: Josh Spradlin - SRF Institute - jefferson Lab, Newport News (VA) USA | Duration: 20 min.
Abstract
High RRR ( > 100) Nb thin films have been frequently fabricated by energetic condensation, via both cathodic arc discharge and ECR Nb plasma method during the Jefferson Lab supported programs. The Nb thin films were deposited on single crystal sapphire (a and c-planes) and MgO on moderate substrate temperate (300C-450C).

Advanced X-ray Diffraction and Electron Back-scattering Diffraction (EBSD) techniques were applied to reveal crystal structures of these Nb thin films. This study particularly used Pole Figures and EBSD to visualize the Reciprocal Lattice Space of the Nb thin films. These representations yielded a new understanding of the Nb thin films, such as the materials crystal texture in two probing depth: 50nm (in the range of SRF London penetration depth) by EBSD, and 2 micron in depth via XRD (covering the Nb/sapphire interface and entire thin films).

Variants of crystal structural symmetries were observed in the pole figures. We assigned them to 3 (or 6) folder Rotation Symmetry or Twinning Symmetry. To confirm the Twinning symmetry, we conduct a computational fitting of the empirical PF plot. For further discussion, twelve Nb B.C.C. Twinning systems are deduced here after a crystallographic study.

By complying with the well-known rule of "Three Dimensional Registry" of Nb/sapphire epitaxy, we could rationalize the observed texture (twinning symmetry, or rotation symmetry) by referring to the Island-Growth model and substrate initiatives. Nevertheless, we witnessed a violation of the law by coating the Nb thin films on c-plane sapphire.

Phenomenological relevance of RRR and texture are presented as is. The high RRR thin films unanimously have near single-crystal-structure (no texture, only monolithic Nb (110) orientation). This provoked us to speculate that the low RRR of Nb thin films might be caused by the high-defect-density zones among the grain boundaries, which in-turn are determined by the island growth model.

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  • 2 thermal-shield boxes, one for TF; one for BK. Which box has a thermal pad for heating.8-thin film samples;
  • 1 instr amplifier: G= 1…1K;2 DAQ-USB to PC4 home made P-S feeds 100mA AC 7Hz;5 read T reading gauge via GPIB3 FFT data process, lock in 7Hz signal.

Spradlin - Texture study of energetic condensed niobium thin films Spradlin - Texture study of energetic condensed niobium thin films Presentation Transcript

  • Texture Study of Energetic Condensed Niobium (Nb) Thin Films
    Kang Seo, Norfolk State University, USA
    Xin Zhao*, L. Philips, J. Spradlin, C. Reece, Jefferson Lab, USA
    M. Krishnan and E. Valderrama, Alameda Applied Sciences Corporation (AASC), USA
    Thin Films and New Ideas for Pushing the Limits of Rf Superconductivity
    Oct 4-6, 2010
    Legnaro National Laboratories, Padua, Italy
  • Outline
    Experimental Method
    Cathodic Arc Deposition (CEDTM by AASC)
    RRR Measurement
    XRD Pole Figure Technique
    EBSD Crystal Orientation Map (Inverse Pole Figure)
    Results
    Deposition Parameters, RRR, XRD, EBSD
    Discussion
    Standard Pole Figures, Nb-Sapphire(Al2O3) “3D-Registry” , Twin Symmetry
    Conclusion
    10/4/2010
    Jlabs SRF Institute
    2 / 18
  • Deposition Method: Energetic Condensation
    CED™ coating inside of furnace tubes
    Cathodic Arc Deposition (CEDTM by AASC. Please refer to Presentation of Dr. Krishnan)
    10/4/2010
    Jlabs SRF Institute
    3 / 18
  • RRR-Tc Testing System
    Thermal Shield Boxes
    Testing Board – 8 samples
    4-Point Probes - Spring-loaded Pins
    • Current Fixture Can Test 8Thin Films Samples per dewar charge.
    • After the upgrade by Nov 2010, it can test 16 samples per dewar.
    • Goal: testing >100 samples per month. Methodically study deposition parameters.
    Bulk Nb Sample Fixture
    10/4/2010
    Jlabs SRF Institute
    4 / 18
  • “Pole Figure” Principle
    To Explore Texture of Poly-crystals
    Source: http://aluminium.matter.org.uk/content/html/eng/0210-0010-swf.htm
    Equatorial Plane is viewed from above to form stereographic projection (Pole Figures)
    10/4/2010
    Jlabs SRF Institute
    5 / 18
  • XRD Pole Figure Experimental Setup
    Nb (110) Single Crystal Pole Figure
    Experimental Steps:
    • Fixed 2θof a {hkl} crystal plane. (Bragg Law 2d{hkl}*sin(θ)=λ)
    • Rotated around Normal Direction (Azimuthalφ, from 0-3600 )
    • Titled off-angle from Normal Direction (ψ, 0-900)
    P.F. is to visualize Reciprocal Lattice Space
    One Crystal Plane in real lattice space is a Pole in reciprocal space
    10/4/2010
    Jlabs SRF Institute
    6 / 18
  • Electron Back Scattering Diffraction (EBSD)
    Spatial Resoluation: 10*30*30 nm
    Kikuchi-bands indicate crystal orientation
    Auto Indexing K-bands via Hough Transformation, Voting, C.I., Calibration
    Orientation Index Map (OIM) shows grain orientations
    Microstructure analysis  (such as Pole Figure) via OIM Analysis software
    Kikuchi diffraction pattern of a Nb Thin Film
    Confidence Index = 0.9
    10/4/2010
    Jlabs SRF Institute
    7 / 18
  • XRD vs EBSD
    10/4/2010
    Jlabs SRF Institute
    8 / 18
  • 3D Epitaxial Relationship of Nb-Al2O3
    It was called by Claassen as “Three-Dimensional (3D) Registry between the two crystal lattices”. The relationship can be denoted as Miller Index asNb[111]//Al2O3[0001], Nb[1,0,-1]//Al2O3[1,0,-1,0]
    10/4/2010
    Jlabs SRF Institute
    9 / 18
  • 3D Epitaxial Relationship of Nb and a-plane Sapphire
    Note: Two equivalents both satisfy “3D-Registry”
    10/4/2010
    Jlabs SRF Institute
    10 / 18
  • Results: CED Nb Films on St.Gobain Al2O3
    (110)
    (110)
    NbI.P.F. color map legend
    10/4/2010
    Jlabs SRF Institute
    11 / 18
  • Results: CED Nb Films on MTI Al2O3
    Another series of Nb thin films on Sapphire (a-plane Al2O3, made by M.T.I. TM) has a similar texture trend
    CED-071810-5
    DOE146-0610A1-3
    DOE146-0610A1-1
    RRR=10, (150/1500C)
    RRR=31, (300/3000C)
    RRR=155, (700/5000C)
    Al2O3
    Al2O3
    Al2O3
    110 Nb
    110 Nb
    110 Nb
    Polycrystalline Thin Films
    Polycrystalline Thin Films
    Monocrystal Thin Films (Epitaxy)
    10/4/2010
    Jlabs SRF Institute
    12 / 18
  • Epitaxial Nb/Al2O3 Thin Films Were Produced
    Sample A, Substr. T= 300C0
    • Standard Nb (110) Pole Figure of Single Crystal
    • XRD Pole Figure of Sample A (Up Right)
    • XRD IvsPhi Survey at Psi=600 orbital( Low Right)
    10/4/2010
    Jlabs SRF Institute
    13 / 18
  • Polycrystalline Nb/Al2O3 Thin Films
    Sample B
    • Standard Nb (110) Pole Figure of Two Sets
    • XRD Pole Figure of Sample B (Up Right)
    • XRD IvsPhi Survey at Psi=600 orbital( Low Right)
    10/4/2010
    Jlabs SRF Institute
    14 / 18
  • Definition of Twin Symmetry
    A complete set of 8 TwinSymmetry systems derives from one b.c.c. lattice.
    Standard Nb (110) Pole Figures of Growth Symmetry
    10/4/2010
    Jlabs SRF Institute
    15 / 18
  • Growth Symmetry and Island Growth Model
    Two equivalents have same probability to grow as nucleation sites
    10/4/2010
    Jlabs SRF Institute
    16 / 18
  • Conclusions
    Niobium Thin Films have been deposited on Al2O3 by CED under different substrate temperatures during deposition and bake prior to deposition.
    Preferred orientations were found in CED samples with lower substrate temperatures during deposition
    10/4/2010
    Jlabs SRF Institute
    17 / 18
  • Acknowledgements
    This research was supported by the US DOE via SBIR grants to AASC. The JLab effort was provided by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177, including supplemental funding provided by the American Recovery and Reinvestment Act.
    10/4/2010
    Jlabs SRF Institute
    18 / 18
  • Backup Slides
    10/4/2010
    Jlabs SRF Institute
    19 / 18
  • Function Generator
    RRR Testing Circuit Schematics
    4-point-probes &
    RRR Testing Sample
    Diff. voltage signal (nV-mV)
    I
    Current source
    Instr. Amp INA121
    Gain 1000
    GPIB cable
    Eight samples in total, each has independent current source and instr. Amp.
    ….
    LabVIEW PC
    8 Ch.
    single input
    DAQ board
    National Instr,
    USB cable
    • Pin1-4: AC Current, 7Hz, Sine Waveform, Amplitude 60mA
    • Pin 2-3: Output Voltage Signal (Sine Waveform). Using FFT to obtain Voltage Amplitude @ 7Hz.
    • Recording both Current and Voltage >> R = V/I
    Thermal diode
    Reading Gauge
    10/4/2010
    Jlabs SRF Institute
    20 / 18