Spradlin - Texture study of energetic condensed niobium thin films


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Texture Analysis of Niobium Thin Films (Josh Spradlin - 20')
Speaker: Josh Spradlin - SRF Institute - jefferson Lab, Newport News (VA) USA | Duration: 20 min.
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

    1. 1. Texture Study of Energetic Condensed Niobium (Nb) Thin Films<br />Kang Seo, Norfolk State University, USA<br />Xin Zhao*, L. Philips, J. Spradlin, C. Reece, Jefferson Lab, USA<br />M. Krishnan and E. Valderrama, Alameda Applied Sciences Corporation (AASC), USA<br />Thin Films and New Ideas for Pushing the Limits of Rf Superconductivity<br />Oct 4-6, 2010<br />Legnaro National Laboratories, Padua, Italy<br />
    2. 2. Outline<br />Experimental Method<br />Cathodic Arc Deposition (CEDTM by AASC)<br />RRR Measurement<br />XRD Pole Figure Technique<br />EBSD Crystal Orientation Map (Inverse Pole Figure)<br />Results<br />Deposition Parameters, RRR, XRD, EBSD<br />Discussion<br />Standard Pole Figures, Nb-Sapphire(Al2O3) “3D-Registry” , Twin Symmetry<br />Conclusion<br />10/4/2010<br />Jlabs SRF Institute<br />2 / 18 <br />
    3. 3. Deposition Method: Energetic Condensation<br />CED™ coating inside of furnace tubes<br />Cathodic Arc Deposition (CEDTM by AASC. Please refer to Presentation of Dr. Krishnan)<br />10/4/2010<br />Jlabs SRF Institute<br />3 / 18<br />
    4. 4. RRR-Tc Testing System<br />Thermal Shield Boxes<br />Testing Board – 8 samples<br />4-Point Probes - Spring-loaded Pins<br /><ul><li> Current Fixture Can Test 8Thin Films Samples per dewar charge.
    5. 5. After the upgrade by Nov 2010, it can test 16 samples per dewar.
    6. 6. Goal: testing >100 samples per month. Methodically study deposition parameters.</li></ul>Bulk Nb Sample Fixture<br />10/4/2010<br />Jlabs SRF Institute<br />4 / 18<br />
    7. 7. “Pole Figure” Principle<br />To Explore Texture of Poly-crystals<br />Source: http://aluminium.matter.org.uk/content/html/eng/0210-0010-swf.htm<br />Equatorial Plane is viewed from above to form stereographic projection (Pole Figures)<br />10/4/2010<br />Jlabs SRF Institute<br />5 / 18<br />
    8. 8. XRD Pole Figure Experimental Setup<br />Nb (110) Single Crystal Pole Figure<br />Experimental Steps:<br /><ul><li>Fixed 2θof a {hkl} crystal plane. (Bragg Law 2d{hkl}*sin(θ)=λ)
    9. 9. Rotated around Normal Direction (Azimuthalφ, from 0-3600 )
    10. 10. Titled off-angle from Normal Direction (ψ, 0-900)</li></ul>P.F. is to visualize Reciprocal Lattice Space<br />One Crystal Plane in real lattice space is a Pole in reciprocal space<br />10/4/2010<br />Jlabs SRF Institute<br />6 / 18<br />
    11. 11. Electron Back Scattering Diffraction (EBSD)<br /> Spatial Resoluation: 10*30*30 nm<br /> Kikuchi-bands indicate crystal orientation<br /> Auto Indexing K-bands via Hough Transformation, Voting, C.I., Calibration<br /> Orientation Index Map (OIM) shows grain orientations<br />Microstructure analysis  (such as Pole Figure) via OIM Analysis software<br /> Kikuchi diffraction pattern of a Nb Thin Film <br />Confidence Index = 0.9<br />10/4/2010<br />Jlabs SRF Institute<br />7 / 18<br />
    12. 12. XRD vs EBSD<br />10/4/2010<br />Jlabs SRF Institute<br />8 / 18<br />
    13. 13. 3D Epitaxial Relationship of Nb-Al2O3<br />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]<br />10/4/2010<br />Jlabs SRF Institute<br />9 / 18<br />
    14. 14. 3D Epitaxial Relationship of Nb and a-plane Sapphire<br />Note: Two equivalents both satisfy “3D-Registry”<br />10/4/2010<br />Jlabs SRF Institute<br />10 / 18<br />
    15. 15. Results: CED Nb Films on St.Gobain Al2O3<br />(110)<br />(110)<br />NbI.P.F. color map legend<br />10/4/2010<br />Jlabs SRF Institute<br />11 / 18<br />
    16. 16. Results: CED Nb Films on MTI Al2O3<br />Another series of Nb thin films on Sapphire (a-plane Al2O3, made by M.T.I. TM) has a similar texture trend<br />CED-071810-5<br />DOE146-0610A1-3<br />DOE146-0610A1-1<br />RRR=10, (150/1500C)<br />RRR=31, (300/3000C)<br />RRR=155, (700/5000C)<br />Al2O3<br />Al2O3<br />Al2O3<br />110 Nb<br />110 Nb<br />110 Nb<br />Polycrystalline Thin Films<br />Polycrystalline Thin Films<br />Monocrystal Thin Films (Epitaxy)<br />10/4/2010<br />Jlabs SRF Institute<br />12 / 18<br />
    17. 17. Epitaxial Nb/Al2O3 Thin Films Were Produced<br />Sample A, Substr. T= 300C0<br /><ul><li> Standard Nb (110) Pole Figure of Single Crystal
    18. 18. XRD Pole Figure of Sample A (Up Right)
    19. 19. XRD IvsPhi Survey at Psi=600 orbital( Low Right) </li></ul>10/4/2010<br />Jlabs SRF Institute<br />13 / 18<br />
    20. 20. Polycrystalline Nb/Al2O3 Thin Films<br />Sample B<br /><ul><li> Standard Nb (110) Pole Figure of Two Sets
    21. 21. XRD Pole Figure of Sample B (Up Right)
    22. 22. XRD IvsPhi Survey at Psi=600 orbital( Low Right) </li></ul>10/4/2010<br />Jlabs SRF Institute<br />14 / 18<br />
    23. 23. Definition of Twin Symmetry<br />A complete set of 8 TwinSymmetry systems derives from one b.c.c. lattice. <br />Standard Nb (110) Pole Figures of Growth Symmetry<br />10/4/2010<br />Jlabs SRF Institute<br />15 / 18<br />
    24. 24. Growth Symmetry and Island Growth Model<br />Two equivalents have same probability to grow as nucleation sites <br />10/4/2010<br />Jlabs SRF Institute<br />16 / 18<br />
    25. 25. Conclusions<br />Niobium Thin Films have been deposited on Al2O3 by CED under different substrate temperatures during deposition and bake prior to deposition.<br />Preferred orientations were found in CED samples with lower substrate temperatures during deposition <br />10/4/2010<br />Jlabs SRF Institute<br />17 / 18<br />
    26. 26. Acknowledgements<br />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.<br />10/4/2010<br />Jlabs SRF Institute<br />18 / 18<br />
    27. 27. Backup Slides<br />10/4/2010<br />Jlabs SRF Institute<br />19 / 18<br />
    28. 28. Function Generator<br />RRR Testing Circuit Schematics<br />4-point-probes &<br />RRR Testing Sample<br />Diff. voltage signal (nV-mV)<br />I<br />Current source<br />Instr. Amp INA121 <br />Gain 1000<br />GPIB cable<br />Eight samples in total, each has independent current source and instr. Amp.<br />….<br />LabVIEW PC<br />8 Ch. <br />single input<br />DAQ board<br />National Instr,<br />USB cable<br /><ul><li>Pin1-4: AC Current, 7Hz, Sine Waveform, Amplitude 60mA
    29. 29. Pin 2-3: Output Voltage Signal (Sine Waveform). Using FFT to obtain Voltage Amplitude @ 7Hz.
    30. 30. Recording both Current and Voltage >> R = V/I</li></ul>Thermal diode<br />Reading Gauge<br />10/4/2010<br />Jlabs SRF Institute<br />20 / 18<br />