Spradlin - Texture study of energetic condensed niobium thin films
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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, 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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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.
Transcript of Spradlin - Texture study of energetic condensed niobium thin films
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
10/4/2010 Jlabs SRF Institute 2 / 18
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.
Testing Board – 8 samples 4-Point Probes - Spring-loaded Pins
Bulk Nb Sample Fixture
10/4/2010 Jlabs SRF Institute 4 / 18
“Pole Figure” Principle
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)
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To Explore Texture of Poly-crystals
XRD Pole Figure Experimental SetupNb (110) Single Crystal
Pole Figure
(011)(101)
(101) (011)
109.480
70.520
Nb
600
900
(110) φ
ψ(110)
Crystal Plane ψ (0) φ (0)
(110) 0 0 (011) 60 54.74 (101) 60 125.26
(1,0,-1) 60 234.74 (0,1,-1) 60 305.26 (1,-1,0) 90 180
(-1,1,0) 90 0
1
•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
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 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
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 as Nb[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”
Nb [111]
Al2O3 [0001]
1800
[100]
[010]
Nb (011)
Nb* (011)
[001]
[1010]
[101]
Nb (0,1,-1) // Al2O3(1,1,-2,0)Nb [1,1,1] // Al2O3 [0001]Nb [1,0,-1] // Al2O3[1,0,-1,0]
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sample A B CLabel AASC-126-015 AASC-126-007 AASC-126-006
Substrate Temp.(0C) 300 250 No heatingRRR 139 7 4
XRD Bragg-Brentano Survey
XRD(110) Pole Figure
EBSD Inverse Pole Figure
40 50 60 70 80 90 100 110 1202Theta-Omega (°)
0
10000
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90000
160000
Inte
nsity
(co
unts
)
40 50 60 70 80 90 100 1102Theta-Omega (°)
0
10000
40000
90000
160000
Inte
nsity
(co
unts
)
40 50 60 70 80 90 100 1102Theta-Omega (°)
0
2500
10000
22500
Inte
nsity
(co
unts
)
(110) (110)
10/4/2010 Jlabs SRF Institute 11 / 18
Nb I.P.F. color map legend
Results: CED Nb Films on St. Gobain Al2O3
40 50 60 70 80 90 1002Theta-Omega (°)
0
2500
10000
22500
40000
Inte
nsity
(co
unts
)
Results: CED Nb Films on MTI Al2O3
RRR=10, (150/1500C) RRR=31, (300/3000C) RRR=155, (700/5000C)
35 45 50 60 70 80 85 952Theta-Omega (°)
0
10000
40000
90000
160000
Inte
nsity
(co
unts
)
35 45 50 60 70 80 85 952Theta-Omega (°)
0
10000
40000
90000
160000
250000
360000
Inte
nsity
(co
unts
)
Al2O3 Al2O3
110 Nb
CED-071810-5DOE146-0610A1-3 DOE146-0610A1-1
Polycrystalline Thin Films Polycrystalline Thin Films Monocrystal Thin Films (Epitaxy)10/4/2010 Jlabs SRF Institute 12 / 18
110 Nb
Al2O3
110 Nb
Another series of Nb thin films on Sapphire (a-plane Al2O3, made by M.T.I. TM) has a similar texture trend
(011)(101)
(101) (011)
109.480
70.520
Nb
600
900
(110) φ
ψ(110)
Epitaxial Nb/Al2O3 Thin Films Were Produced
Standard Nb (110) Pole Figure of Single Crystal XRD Pole Figure of Sample A (Up Right) XRD I vs Phi Survey at Psi=600 orbital( Low Right)
Nb (110)
φ00
109.80
70.80
108.80
70.60
Sample A, Substr. T= 300C0
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Polycrystalline Nb/Al2O3 Thin Films
Standard Nb (110) Pole Figure of Two Sets XRD Pole Figure of Sample B (Up Right) XRD I vs Phi Survey at Psi=600 orbital( Low Right)
41.60
Nb (110)
φ
00
68.90
89.80
690
48.80
69.50
Sample B
0
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90
0
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6070
8090100110
120
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0
10
20
30
40
50
60
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(011)(101)
(1,0,-1) (0,1,-1) 38.960
70.520
Nb
(110) φ
ψ 70.50
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Twin Sym
metry
Twin Direction
Twin Plane Normal Plane
1 [1,-1,1] (-1,1,2) (1,1,0) 2 [-1,1,-1] (-1,1,2) (1,1,0)
3 [1,-1,-1] (1,-1,2) (1,1,0) 4 [-1,1,1] (1,-1,2) (1,1,0) 5 [-1,-1,1] (1,1,2) (-1,1,0)
6 [-1,-1,-1] (-1,-1,2) (-1,1,0)
7 [1,1,-1] (1,1,2) (-1,1,0)
8 [1,1,1] (-1,-1,2) (-1,1,0)
1
Definition of Twin Symmetry
• A complete set of 8 Twin Symmetry systems derives from one b.c.c. lattice.
θ
Twin Plane Twin DirectionNormal Plane
0
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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
10
20
30
40
50
60
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80
90
0
10
20
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8090100110
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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
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
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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
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