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.

Testing Board – 8 samples 4-Point Probes - Spring-loaded Pins

Bulk Nb Sample Fixture

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“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

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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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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

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

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nsity

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nsity

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(110) (110)

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Nb I.P.F. color map legend

Results: CED Nb Films on St. Gobain Al2O3

40 50 60 70 80 90 1002Theta-Omega (°)

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nsity

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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 (°)

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nsity

(co

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nsity

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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

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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

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(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]

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(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

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