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Nanoscale Electrodynamics Measurements with Radical New Forms of Microwave Microscopy

Nanoscale Electrodynamics Measurements with Radical New Forms of Microwave Microscopy. Steven Anlage, Michael Fuhrer. ONR AppEl Review 26 August, 2010. Work funded by ONR and DOE. UMD Microwave Microscopy Group. Faculty: Steven Anlage Michael Fuhrer Graduate Student Tamin Tai

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Nanoscale Electrodynamics Measurements with Radical New Forms of Microwave Microscopy

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  1. Nanoscale Electrodynamics Measurements with Radical New Forms of Microwave Microscopy Steven Anlage, Michael Fuhrer ONR AppEl Review 26 August, 2010 Work funded by ONR and DOE

  2. UMD Microwave Microscopy Group Faculty: Steven Anlage Michael Fuhrer Graduate Student Tamin Tai Undergraduate Students John Abrahams Post-Doc Behnood Ghamsari Collaborators: Alexander Zhuravel, Kharkov, Ukraine Alexey Ustinov, Karlsruhe Inst. Tech. Dragos Mircea, Western Digital Vladimir Talanov, Neocera Lance Cooley, FermiLab Gigi Ciovatti, Jefferson Lab Funding: ONR AppEl and DOE

  3. All-electric and munitions-free ships require new materials technologies Superconducting RF cavities for free-electron lasers Superconducting tapes and wires for compact, efficient motors ‘Quantum’ materials with novel properties

  4. Motivations The development of new materials with new functionalities depends on establishing structure / property relationships New forms of microscopy help to accelerate the development of these novel materials Development of new Nano-Electromagnetic devices requires understanding of electrodynamics at the nano-scale We are developing two new types of microscopy to establish structure / property relations at high frequency and low temperatures, under conditions where the materials will be utilized Near-Field Microwave Microscopy of Nb for SRF applications Laser Scanning Microscopy of superconductors and novel electronic materials

  5. Localized Defects on Nb SRF Cavities These defects can lead to hot spots on accelerator cavity within operating frequency region (1-2 GHz) However, many defects are benign. How to distinguish the ‘good’ ones from the ‘bad’ ones? Grain Boundaries welds, oxidation,hydrogen poisoning welds, oxidation,hydrogen poisoning T. Bieler Mich. State Univ. 500 x 200 mm pit http://www.helmholtz-berlin.de/events/srf2009/programs/tutorials_de.html

  6. APPROACH Near-Field Microwave Microscopy* GOAL: To establish links between microscopic defects and the ultimate RF performance of Nb at cryogenic temperatures APPROACH: 1) Stimulate Nb with a concentrated and intense RF magnetic field • Drive the material into nonlinearity (nonlinear Meissner effect) • Why the NLME? It is very sensitive to defects… • Measure the characteristic field scale for nonlinearity: JNL 4) Map out JNL(x,y) → relate to previously-characterized defects *S. M. Anlage, V. Talanov, A. Schwartz, "Principles of Near-Field Microwave Microscopy," in Scanning Probe Microscopy: Vol. 1, edited by S. V. Kalinin and A. Gruverman (Springer-Verlag, New York, 2007), pages 215-253.

  7. Nonlinear Near-Field Microscopy of Superconductors P3f : NLME Nonlinearities Pinput sample surface coaxial probe K(x,y) loop Superconductor Current distribution geometry factor Induce high m0K ~ 200 mT (Hc of Nb) K(x,y) sharply peaked in space ► Better spatial resolution D. Mircea, S. Anlage, Phys. Rev. B 80, 144505 (2009) + references therein

  8. What do We Learn About the Superconductor? on YBCO P3f(x) JNL(x) Position x Defect 1 Defect 2 Measured at T=60 K (below Tc of YBCO) Phys. Rev. B 72, 024527 (2005)

  9. How to Generate Strong RF Magnetic Fields? Cu coils Permalloy shields m ~2 m Write Pole Read Sensor 2 mm Air bearing surface RF Magnetic Fields Permalloy Magnetic Write Head Magnetic recording heads provide strong and localized BRF Side View SEM picture of the magnetic write head gap Bottom View BRF ~ 1 Tesla (in gap) Gap Lateral size ~ 100 nm x few-100 nm Reference: IEEE Trans Magn. Vol . 37, No. 2 pp.613-618 2001

  10. Experimental Setup RF Coil on slider Superconductor Goals: BRF ~ 200 mT Lateral size ~ 100 nm We need higher BRF and strongly localized field distributions Probe Head Gimbal Assembly (HGA)

  11. Measurements on Superconductors At a fixed location on MgB2 film Excited power: 12 dBm; Excited frequency: 3.75GHz Noise floor MgB2 Film (25nm)/SiC A peak in P3f(T) near the Tc of MgB2 is found. No other P3f peak is found below Tc. It implies there is no defect near this measurement point. Samples come from Prof. Xiao-Xing Xi Temple University, Philadelphia, PA

  12. Tc Noise floor Measurements on Tl2Ba2CaCu2O8 Film At a fixed location Excited power: 6 dBm Excited frequency: 3.75 GHz Vortex or defects/ grain boundary contribution

  13. Head Gimbal Assembly (HGA) Top surface of bulk Nb (thickness: 0.1 inch) Pit on Nb Copper cold plate Challenges for Measurements on Nb bulk materials • Probes may cause localized heating of Nb samples. • Temperature of cold plate reaches 4.2K but Nb surface remains warmer. (Next step: thermal grounding of probe and positioner) • Magnetic write head probe is still too far away from the superconductor surface.(Next step: nm-level positioning control)

  14. Photolithography Result (thanks to Dr. Cihan Kurter) Current Work---Micro Loop Design Simulation Data from HFSS (Gregory Ruchti ) Micro loop design can enhance the current geometry factor G and increase our spatial resolution.

  15. Laser Scanning Microscopy: Principle of the measurement modulated laser resonator transmission laser OFF Pout |S21(f0)|2 Pin laser ON |S21(f0)|2 f f0 co-planar resonator f0 ~ 5.2 GHz D|S12|2 ~ [lJRF(x,y)]2 A dl Local heating produces a change in transmission coefficient proportional to the local value of JRF2 J. C. Culbertson, et al. J.Appl.Phys. 84, 2768 (1998) @ NRL A. P. Zhuravel, et al., Appl.Phys.Lett. 81, 4979 (2002)

  16. Typical Spatial Profile of RF Photoresponse Along a Lateral Cross Section of the Resonator Strip YBCO/LaAlO3 CPW Resonator T = 79 K P = - 10 dBm f = 5.285 GHz fmod = 99.9 kHz 1 x 8 mm scan P1 = in-plane rotated grain P2 = crack in YBCO film P3 = LAO twin domain blocks Wstrip = 500 mm

  17. Imaging of a YBa2Cu3O7 / LaAlO3 Resonator Optical reflectivity DC Photoresponse Low-T RF PR “PR” = Photo-response Room Temp. Thermoelectric PR A. Zhuravel, et al., J. Appl. Phys. 108, 033920 (2010)

  18. Corner “A2” Detail of YBCO / LAO Resonator Optical Reflectivity RF PR A. Zhuravel, et al., J. Appl. Phys. 108, 033920 (2010) 25 mm

  19. Laser Scanning Microscope @ UMD LSM in Karlsruhe, Germany UMD Microscope: configured for bulk superconductors, closed cycle refrigerator JLab Microscope: built inside a Nb SRF cavity

  20. Current and Future Work Complete the UMD Laser Scanning Microscope Closed cycle refrigerator for week-long runs Ukraine collaborator (Zhuravel) visits to commission the microscope Preliminary results from Karlsruhe collaboration RF Defect Imaging in bulk Nb

  21. Collaborative Work on Nb Cavity Laser Scanning Microscope at Jefferson Lab Built by G. Ciovatti and P. Kneisel @ JLab

  22. Nano Materials Growth of aligned carbon nanotubes Wiring of carbon nanotubes Pt 3 CNTs Enrique Cobas, M. Fuhrer Cr CNT Schottky diodes E. Cobas, Appl. Phys. Lett. 93, 043120 (2008) Diodes rectify for frequencies up to 40 GHz Estimates: fcutoff ~ 100’s of GHz in some devices

  23. High Resolution Microwave Microscopy Scanning Tunneling Microscope (STM)- Assisted Microwave Microscopy Atif Imtiaz, et al., Appl. Phys. Lett. 90, 143106 (2007) Atif Imtiaz, et al., J. Appl. Phys. 97, 044302  (2005) STM Topography (constant current) Cx Rx Simple circuit model of probe-sample interaction

  24. Experiments Prepare nanotubes suspended over a trench A100 mm-long CNT should resonate at 10 GHz Excite resonance with microwave microscope or in a CPW geometry Luttinger liquid physics

  25. Intrinsic Inhomogeneity in Correlated-Electron Materials Electron-Hole Puddles in Graphene Scanning SET microscopy 2 mm x 3 mm, 0.3 K J. Martin, Nature Physics (2008) Electron nematic phase in Co-Fe-As Chuang, Science (2010)

  26. Conclusions Near-Field Microwave Microscopy • A magnetic write head, which can generate strong RF fields on sub-mm length • scales, is successfully integrated into the near field microwave microscope • operating at cryogenic temperatures. • A clear reproducible nonlinear response signal from TBCCO and MgB2 are • obtain by this magnetic write head probe. • Further improvements will enable SRF defect microscopy on bulk Nb surfaces. Laser Scanning Microscopy The LSM gives unique insights into structure / property relations at ~ mm length scales Preliminary data on bulk Nb resonators is encouraging Microscopy-related ongoing research efforts: Purely evanescent probe: Time-reversed microscopy to eliminate far-field radiation, S. M. Anlage, et al., Acta Physica Polonica A 112, 569 (2007) Use of Metamaterials to enhance evanescent waves and resolution, M. Ricci, et al., Appl. Phys. Lett. 88, 264102 (2006)

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