Texture Study of Energetic Condensed Niobium (Nb) Thin Films Thin Films and New Ideas for Pushing the Limits of Rf Superconductivity Oct 4-6, 2010 Legnaro National Laboratories, Padua, Italy 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
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Spradlin - Texture study of energetic condensed niobium thin films
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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Texture Study of Energetic Condensed Niobium (Nb) Thin Films
Thin Films and New Ideas for Pushing the Limits of Rf Superconductivity
Oct 4-6, 2010Legnaro National Laboratories, Padua, Italy
Kang Seo, Norfolk State University, USAXin Zhao*, L. Philips, J. Spradlin, C. Reece, Jefferson Lab, USAM. Krishnan and E. Valderrama, Alameda Applied Sciences
Corporation (AASC), USA
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
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Deposition Method: Energetic Condensation
Cathodic Arc Deposition (CEDTM by AASC. Please refer to Presentation of Dr. Krishnan)
CED™ coating inside of furnace tubes
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RRR-Tc Testing SystemThermal Shield Boxes
• Current Fixture Can Test 8 Thin 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.
•Fixed 2θ of a {hkl} crystal plane. (Bragg Law 2d{hkl}*sin(θ)=λ)•Rotated around Normal Direction (Azimuthal φ, from 0-3600 )•Titled off-angle from Normal Direction (ψ, 0-900)
Experimental Steps:
P.F. is to visualize Reciprocal Lattice SpaceOne Crystal Plane in real lattice space is a Pole in reciprocal space
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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 orientationsMicrostructure analysis (such as Pole Figure) via OIM Analysis software
Kikuchi diffraction pattern of a Nb Thin Film Confidence Index = 0.9
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xinzhao
XRD vs EBSDXRD EBSD
Probing Area (Diffraction Area)
10*17mm (selectable by X-ray aperture)
30*30 nm.By rastering e-beam, it can scan a large area. Single frame Limited by SEM magnification
Probing Depth (Diffraction depth)
1 to 2 microns <50nm
Pole Figures Yes Yes
Grain size sensitivity
any Must >50 nm
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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 as Nb[111]//Al2O3[0001], Nb[1,0,-1]//Al2O3[1,0,-1,0]
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3D Epitaxial Relationship of Nb and a-plane Sapphire
• A complete set of 8 Twin Symmetry systems derives from one b.c.c. lattice.
θ
Twin Plane Twin DirectionNormal Plane
0
10
20
30
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50
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80
90
0
10
20
30
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6070
8090100110
120
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240250
260 270 280290
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0
10
20
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40
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(011)(101)
(1,0,-1) (0,1,-1) 38.960
70.520
Nb
(110) φ
ψ 70.50
Standard Nb (110) Pole Figures of Growth Symmetry
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Growth Symmetry and Island Growth Model
Two equivalents have same probability to grow as nucleation sites
Nb(110)
Nb*(110)
Nb(110)
Nb*(110)
Twin Boundary
Al2O3
a-plane
Nb [111]
Al2O3 [0001]
1800
[100]
[010]
Nb (011)
Nb* (011)
[001]
[1010]
[101]
0
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90
0
10
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6070
8090100110
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260 270 280290
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0
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(011)(101)
(1,0,-1) (0,1,-1) 38.960
70.520
Nb
(110) φ
ψ 70.50
θ
Twin Plane Twin DirectionNormal Plane
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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
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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.
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Backup Slides
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RRR Testing Circuit Schematics
I
USB cable
Function Generator4-point-probes &RRR Testing Sample
Instr. Amp INA121 Gain 1000
….Eight samples in total, each has independent current source and instr. Amp.
Current source
8 Ch. single inputDAQ boardNational Instr,
Diff. voltage signal (nV-mV)
LabVIEW PC
GPIB cable
Thermal diodeReading Gauge
•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