ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 1 ECR Deposition of Niobium ECR plasma principle Cavity deposition system prototype Surface treatment NbN surface coating A-M. Valente, L. Phillips, H. Wang, A. Wu, R. Bundy, T. Goodman, R. Rimmer, C. Reece, Jefferson Lab G. Wu, Fermilab H. Padamsee, Cornell University

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 2 Illustration of the energetic vacuum deposition by ECR plasma Wu, G., et al., J. Vac. Sci. Technol. A Vol. 21, No. 4, (2003)

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 3

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 4 Right electron kinetic energy Total ionization cross section of 5 outer shell electrons Off-resonant ECR to achieve longer electron life and right ionization energy

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 5 Niobium Plasma Ion Energy Distribution measured by the Analyzer

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 6 (1)14kW rod-fed E-gun (2)9000 l/s cryopump system (3)bucking coil for E-gun (4)top and bottom iron yokes (outer iron shield is removed for illustration) (5)center coils (6)Nb grid tube (7)bias insulator (8)WR284 waveguide E-bend and horn to the grid tube (9)“T” vacuum chamber (10)top pancake coil (11)Cu cavity (12)bottom pancake coil. ECR cavity deposition system Potential use for surface cleaning and Nb 3 Sn, NbN coatings

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 7 Large volume of ECR magnetic field Sample deposition system 7.5kW hearth, 130 A/s Cavity deposition system 15 kW Rod-fed, 100 A/s Magnetic field Slight radial confinement

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 8 Miller welder 1400 A Lambda EM 250 A x GHz Magnetron RF power meterCoil tempera- ture monitor E-beam power Copper coil E-gun viewer window Water manifold Argon feed line CryopumpYoke iron Ion Gauge, two pancake coils and one bucking coil not visible

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 9 Inside E-gun chamber

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 10

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity /250W RF Ar: 1.2e-5 Torr 238/250W RF Ar: 2.9e-5 Torr ( )W/293 W Nb: ~3.5 kW Ar: 15.7 eV Nb: 7.0 eV

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 12 Summary of thin film sample Niobium Ion Energy is around 63 eV without bias voltage, and controllable. Cryogenically, the process achieves a reasonably high RRR niobium thin film with excellent superconducting transition temperature and width. RRR appears to be more closely related to the film thickness than to the deposition energy. Epitaxial growth of niobium on sapphire has been achieved. The substrate bias voltage of -60 V is believed to be the preferred value based on the transition width, the crystal orientation spread, and the AFM results. For a copper substrate, a better film quality likely requires higher deposition energy than sapphire substrate, which needs further studies. Nb-Cu sample surfaces are smooth locally Nb-Cu surfaces may have much less hydrocarbons and other residuals or contaminants as compared with those on the Nb surfaces obtained conventionally (BCP or EP). Nb-Cu samples appear to have more oxygen on the surfaces and oxygen penetrates deeper into the interior of the samples. This may be resulted from the residual gases in the deposition chamber and from the fact that the grain size of Nb-Cu is small.

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 13 A multilayer sample of Nb-NbO x -Nb Copper substrate was prepared by electropolishing. First layer of Nb was deposited at 500 V bias voltage. Exposed to air to form Nb oxides. Second layer (thicker) of Nb was deposited at 60 V bias voltage. TEM sample prepared (FIB) and analyzed at SANDIA TEM by T. Renk, P. Provencio, SNL

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 14 Cu substrate 10 nm Nb 3-5 nm Nb oxides Nb

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 15 Zoomed view of the interface

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 16 Plasma surface treatment Surface smoothening through coating Use (NEB) method to find energy barriers for various diffusion processes on the surface. MD for lattice dynamics KMC/MD combination to simulate the film growth J. Pomeroy, Ph.D Dissertation, Cornell University Potential cross the surface by ASE/Dacapo

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 17 A. Wu, Jlab RMS = 251 nm EPRMS = 35 nm BEP RMS = 1274 nm BCPRMS = 94 nm Nb/Cu

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 18 Alternative processes for bulk niobium cavity treatment Degrease or light etching Water rinsing De-oxidation 1,000 nm smooth coating 800  C bake HPW rinsing After RF tuning, prepare a UHV degrease Light water rinsing or ultrasonic water rinsing High impact energy Ar ion pre-etching of the cavity ECR deposition of a smoothening high purity Nb layer 2 hour 800  C bake to decrease the hydrogen content and moderate re-crystallization High pressure water rinsing before final assembly

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 19 G. Wu, et al., Thin Solid Film, Vol 489/1-2 pp 56-62, 2005 A. Wu, et al., PAC05, Knoxville, TN, 2005 O. Hellwig, Ph.D dissertation, Ruhr-Universität Bochum, 2000 Some mosaicity is inevitable in film. That is less detrimental than grain boundary, yet prone to deep oxidation and possible RF dissipation.

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 20 NbN by plasma injection? ECR plasma of Nitrogen can be achieved at low pressure, N + can travel to the substrate without much energy loss Bias voltage can be reversed to stop ion impact immediately (To lessen the metallic Nb 2 N forming) Bias voltage could potentially be adjusted for proper phase control: -NbN or Nb 3 N 4 (insulator)

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 21 Acknoledgement JLAB ECR thin film collaboration: Cornell: H. Padamsee (LEPP), L. Hand (Physics) College of William and Mary: M. Kelley SANDIA: T. Renk, P. Provencio Black Laboratory: R. Crooks LANL: T. Tajima

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 22 TEM cross section view – JLNB-CU-60 Electron diffraction pattern

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 23 TEM cross section view – JLNB-CU-70 Electron diffraction pattern

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 24 TEM cross section view – JLNB-CU-80 Electron diffraction pattern

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 25 TEM cross section view – JLNB-CU-90 Electron diffraction pattern

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 26 TEM cross section view – JLNB-SA-100 Electron diffraction pattern

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 27 X-ray diffraction pattern for sputtered niobium film Reference: D. Tonini, et al. SRF2003 proceedings

ECR Deposition of Niobium 10/09/2006 Thin Films and new ideas for pushing the limits of RF superconductivity 28 X-ray diffraction pattern for niobium film by vacuum arc deposition Reference: R. Russo, et al. SRF2003 proceedings