The Applied Superconductivity Center The National High Magnetic Field Laboratory Florida State University 5 th SRF TF Understanding of growing mechanism of high RRR Nb films on MgO substrate ZH. Sung 1, P.J. Lee 1, and L. Cooley 1 M. Krishnan 3, E. Valderrama 3, and C. James 3 X. Zhao 4 and C.E. Reece 4 1. NHMFL-ASC, FSU, 2. FNAL, 3. AASC, and 4. TJNAF Acknowledgements: The work is based upon work supported by FNAL Award Number and the State of Florida.

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Motivations Replacing bulk Nb with Nb or other superconductor (MgB 2, YBCO, Pnictide..) coated Cu cavities could reduce SRF fabrication cost. However, how and why Nb film properties achieve bulk properties (RRR ) is still unclear. In addition, there is a lack of exploration of the effect of surface properties within 40 nm penetration depth of Nb thin film on Superconducting RF properties.

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Methodology Local and global superconducting properties and its relative surface and micro structure properties Magnet-optical (MO) imaging SLCM (Scanning Laser Confocal Microscopy) and AFM (Atomic Force Microscopy) EBSD-OIM (Electron Back Scattered Diffraction-Orientation Imaging Microscopy) Film grown properties by atomic structural and chemical analysis Atomic resolution (sub-Å) TEM/STEM (scanning transmission electron microscopy) EELS (Electron Energy Loss Spectroscopy)

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y 3 Different Nb thin films grown on MgO (100) substrate by Energetic Condensation Deposition (CED) DOE AMC-4CED CED T annl. /T sub. 150/150500/500700/700 RRR * XRD Pole Figure(110)(110&200)(200) EBSD * Mixed Kikuchi patternd(110) and (100)(100) only *RRR was measured with 4 point transport by Dr. Zhao at TJNAF *EBSD was measured with LaB 6 by Dr. Zhao at TJNAF

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y RRR of Nb thin films on MgO substrates Pole Figures show change in crystal orientation from 110 to 200 at higher temperature Courtesy of M. SRF 2011, PRST-AB (2012) RRR=7, 150/150RRR=196, 500/500RRR=316, 700/ & Polycrystalline Monocrystal with two orientations Monocrystal with 100 orientation

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y 21.6% Intrinsic growth misfit (film vs substrate lattice parameter!) M. Krishnan et al., Supercond. Sci. Technol. 24 (2011) Lower misfit ratio indicates less intrinsic defects on the film structure! – Longer mean free path

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Three-dimensional epitaxy relationship of Nb/MgO(100)* Illustration of three types Nb/MgO(100) epitaxial relationship, as proposed by Hutchinson et al *. 1.*E. Hutchinson and K. H. Olsen, “Substrate Condensate Chemical Interaction and the Vapor Deposition of Epitaxial Nb Films”, J. Appl. Phys. 38, 4933 (1967). 2.J. E. Mattson, Eric E. Fullerton, C. H. Sowers, and S. D. Bader, “Epitaxial growth of body-centered-cubic transition metal films and superlattices onto MgO (111), (011), and (001) substrates”, J. Vac. Sci. Technol. A 13, 276 (1995).

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y R q = 4.36 nm R a = 3.38 nm RRR-7 Grain structure becomes “Ordered” as RRR increases SEM BSE image RRR-196RRR-316 R q = 5.34 nm R a = 4.29 nm R q = 10.3 nm R a = 8.37 nm Surface roughness by AFM SCLM showed that particles on the surface of each films have ~ µm height profile

Grain structure difference by EBSD-OIM RRR-7 SEM BSE image RRR-196RRR-316 Plan view Transverse Transverse Transverse IPF map of Nb MgO layer Step size ≈ 0.05µm using Field Emission Gun

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Local patterning for MO imaging Cut-out piece (2mm by 8mm) from the as-received Bridged pattern by FIB’ing Coarse cut by a laser Each sample were patterned by FIB for better imaging of local variation of superconducting properties, and this pattern was isolated from the substrate by coarse laser cutting RRR-7 RRR- 196 & RRR mm 1mm

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y 5 o GB  = J b /J c ~ 0.5 J b =0.5J c Magnetic Flux Behavior and Current Distribution on high quality (high current) YBCO CC with around 5 o GRAIN BOUNDARY A.A. Polyanskii, A. Gurevich, A.E. Pashitski, N.F. Heinig, R.D. Redwing, J.E. Nordman, and D.C. Larbalestier, Phys. Rev. B, 53, 8687, (1996). YBa 2 Cu 3 O 7-δ on [001] symmetrical tilted SrTiO3 bi-crystal

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y RRR-7 ZFC T=6.9K H=10 mT FC T=6.9K H=0 mT after 16mT FC T=5.5 K H=0mT after H=4mT RRR-196 ZFC T=5.5K H=4 mT RRR-316 FC T=5.5 K H=0mT after H=10.4mT ZFC T=5.5 K H=-2 mT Very clear roof pattern contrast indicates higher critical density properties in RRR- 316 than others Higher RRR film shows higher circulating current! MO imaging by A. A. Polyanskii

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Atomic structure and chemistry of RRR-7 MgO Nb MgO substrate Nb BF TEM image Columnar structure DP of MgO [002] Arc shape of Nb Diffraction Pattern by columnar structure DP at the interface RRR-7 Growth of fiber grain

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y MgO substrate Nb BF TEM image MgO [002] Nb [001] Nb [011] DP at the interface STEM ADF Nb MgO substrate Inverse FFT Differently ordered atomic structure Misfit dislocations Misfit: % at RRR-7 film RRR-7 Nb (011) // Mg (002)

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Many of differently ordered structure within a columnar grain STEM ADF STEM BF RRR-7 Nb MgO substrate Nb A Nb layer was not uniformly deposited layer by layer at lower annealing temperature. “O” profile at the interface by EELS ~1-2nm thickness of the interface

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Atomic structure and chemistry of RRR-196 MgO Conductor – Mounting material Nb MgO Nb Nb Columnar GB

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y RRR-196 MgO [002] Nb [110] Nb (011) // Mg (002) Misfit: 10.5% at RRR-196 film Nb MgO substrate NbNb Highly misordered structure within a columnar grain

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Atomic structure and chemistry of RRR-316 MgO Nb Nb MgO substrate STEM ADF Uniformly distributed defects Nb MgO substrate Very epitaxially grown Nb atomic layer RRR-316 STEM ADF “O”

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y RRR-316 Uniformly distributed misfit dislocations Nb MgO substrate Inverse FFT Uniformly deposited Nb atomic layers Nb MgO substrate Nb STEM ADF STEM BF STEM ADF

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y (1) (2) MgO [002] Nb [110] Nb (011) // Mg (002) (1) Misfit: 10.5% Nb (002) // Mg (002) by XRD

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y (1) (2) MgO [111] Nb [110] Nb (002) // Mg (011) (2) Misfit: 4.5% Nb (002) // Mg (002) by XRD

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y SamplesParallel directions% misfit RRR-7Random fibers [110]Nb // [200]MgO10.5% [020]Nb // [200]MgO28.02% RRR-196Mixed[101]Nb // [200] MgO RRR-316One structure[101]Nb// [200] MgO10.5% Or [110]Nb // [111] MgO4.53% 1.*E. Hutchinson and K. H. Olsen, “Substrate Condensate Chemical Interaction and the Vapor Deposition of Epitaxial Nb Films”, J. Appl. Phys. 38, 4933 (1967). 2.J. E. Mattson, Eric E. Fullerton, C. H. Sowers, and S. D. Bader, “Epitaxial growth of body-centered-cubic transition metal films and superlattices onto MgO (111), (011), and (001) substrates”, J. Vac. Sci. Technol. A 13, 276 (1995).

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Nb oxide Atomic structure by Cs-corrected STEM RRR 316 Nb film by CED Nb (001) Oxide Nb Nb Au-Pd Oxide Nb Nb Au-Pd STEM ADF STEM BF Cu 10nm

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Summary As substrate annealing : target deposition temperature (T annl /T sub ) is increased, Nb atomic layer grows more uniformly layer by layer on the MgO substrate. At sufficiently high T annl /T sub, the intrinsic mismatch % between the Nb matrix and MgO substrate decreases from 22% (theoretical) or 28% (from electron diffraction pattern) to 10.5% or 4.5% (RRR-316). The interface of between Nb matrix and MgO is ~1 nm thick and this layer does not vary for the different RRR value films. …. Some more analysis related to surface oxide structure is coming….

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y Films Crystal Structure Depend on Thin films (Nb/MgO)  XRD Pole figures and Bragg-Brentano spectra show change in crystal structure of Nb from (110) to (200) on MgO as temperature is increased RRR=7, Tc=9.0K RRR=196, Tc=9.25K RRR=316, Tc=9.25K 200 Nb 110 Nb MgO 110 Nb 200 MgO C/150 0 C C/500 0 C700 0 C/700 0 C Annealin g T/ Substr. T EBSD I.P.F CED 03CED 09DOE XRD P.F. XRD Bragg No K-Pattern Sample

Applied Superconductivity Center National High Magnetic Field Laboratory Florida State Universit y STEM ADF STEM BF RRR-316 Nb MgO substrate Trace for grain growth domain structure “O” “Nb” & “Mg” profile by EELS ~1nm thickness of the interface O core-loss Nb Mg