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Ekaterina Dikarov ( Suhovoy )

Development of high sensitivity, high resolution ESR and its applications for studying solar cells. Ekaterina Dikarov ( Suhovoy ). m s =+1/2 . Energy . m s =-1/2 . B field . What is ESR?. ESR- Electron Spin Resonance. MW induces transition between two energy levels .

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Ekaterina Dikarov ( Suhovoy )

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  1. Development of high sensitivity, high resolution ESR and its applications for studying solar cells Ekaterina Dikarov (Suhovoy )

  2. ms=+1/2 Energy ms=-1/2 B field What is ESR? ESR- Electron Spin Resonance MW induces transition between two energy levels. Spin & Magnetic Field interaction. Paramagnetic centers

  3. 100 µm ESR Imaging E1 E2 B0 100 µm Optical image B0 Frequency 2D image with 3µm resolution

  4. The sensitivity and resolution challenge • Signal-to-noise-ratio (SNR) (Pulsed induction detection ESR) : Magnetization Sample volume MW frequency Quality factor Detection bandwidth Resonator volume Temperature Conventional ESR: Spin sensitivity : ~ 108-109 spins. Imaging resolution : Limited to ~ 20-30 μm

  5. ESR and solar cells: requirements and challenges Dangling bonds defects Less than 1015 spins/cm3 Thin layers ~1μm Impurities Dopants Heterogeneous samples Background signals Short relaxation times • What is needed: • Increased sensitivity :1-104 electron spins. • Improved image resolution: 10-1000 nm.

  6. Pulsed ESR imaging system Microwave reference source Pulsed microwave bridge Gradient coils drivers Cryogenic probe Electromagnet Gradient coils’ structure Temperature controller Cryogenics Resonator and sample holder Control PC

  7. Dielectric resonator - minimization High permittivity dielectric resonators 2.2 mm @ 17 GHz 1.2 mm @ 35 GHz Conventional ESR resonator Dielectric resonator (first generation) Relatively high Q ~ 1000 17 GHz – 107 spins in 1 h at RT Microwave dielectric resonator (TiO2) 35 GHz – 106 spins in 1 h at RT

  8. Going down further in size – New surface resonators ~14 GHz – 104 spins in 1 h at 5K Twig, Y., Suhovoy, E., and Blank, A., Review of Scientific Instruments81 (2010) 104703 Twig, Y., Suhovoy, E., Hutchison, W. D., and Blank, A., Review of Scientific Instruments, 82 (2011) 076105. Twig Y., Dikarov E., and Blank A., Journal of Magnetic Resonance, 218 (2012) 22-29.

  9. Poly-crystalline silicon thin layers (PV) Sample • 1.2 μm thin layer. • Grain size ~ 0.1μm. • Defect density = 9x1017cm-3 • ~ 107 defects in measured volume. (in the surface resonator). Surface resonator Conventional ESR resonator (10K): Surface resonator (10K):

  10. Imaging results 2D ESR image for 10 µm thick layer of phosphorous doped 28Si, taken at 10K.

  11. Future plans • Smaller resonators. • Superconducting surface resonators. • Higher frequencies.

  12. Magnetic Resonance Group members: • Prof. AharonBlank • Dr. Ygal Twig • Dr. Lazar Shtirberg • AlonPlattner • Michael Levit • Alex katchlis • KseniaSirota • OmriArbiv • GubrailShakkour • RamiMaymon • MadaHashem • Itai Katz • Helen Wolfson

  13. Thank you for your attention

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