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Ekaterina Dikarov (Suhovoy )
Development of high sensitivity, high resolution ESR and its
applications for studying solar cells
What is ESR?
ESR- Electron Spin Resonance
Spin & Magnetic Field interaction.
MW induces transition between two energy levels.
ms=+1/2
ms=-1/2
B field
Ene
rgy
hBE 0
0B
Paramagnetic centers
ESR Imaging
Optical image
2D image with 3µm resolution
100 µm
100 µm
B0
Frequency
B0
E1
E2
The sensitivity and resolution challenge
QfTkV
MVSNR
bc
v
8
2 00second onepulse
Resonator volume
Magnetization
Quality factor
Sample volume
Temperature
Detection bandwidth
MW frequency
Signal-to-noise-ratio (SNR) (Pulsed induction detection ESR) :
Conventional ESR:
Spin sensitivity : ~ 108-109 spins.
Imaging resolution : Limited to ~ 20-30 μm
What is needed:
Increased sensitivity :1-104 electron spins.
Improved image resolution: 10-1000 nm.
ESR and solar cells:requirements and challenges
Dangling bonds defects
Impurities Dopants
Less than 1015 spins/cm3
Thin layers ~1μm
Heterogeneous samples
Short relaxation times
Background signals
Pulsed ESR imaging system
Microwave reference source
Pulsed microwave bridge
Gradient coils drivers
Electromagnet
Temperature controller
Control PC
Cryogenics
Cryogenic probe
Gradient coils’ structure
Resonator and sample holder
Dielectric resonator - minimization
2.2 mm @ 17 GHz
1.2 mm @ 35 GHz
Microwave dielectric resonator (TiO2)
High permittivity dielectric resonators
Conventional ESR resonator
17 GHz – 107 spins in 1 h at RT
35 GHz – 106 spins in 1 h at RT
Relatively high Q ~ 1000
Dielectric resonator (first generation)
Going down further in size – New surface resonators
Twig, Y., Suhovoy, E., and Blank, A., Review of Scientific Instruments 81 (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.
~14 GHz – 104 spins in 1 h at 5K
Poly-crystalline silicon thin layers (PV)
• 1.2 μm thin layer.• Grain size ~ 0.1μm.• Defect density = 9x1017cm-3
• ~ 107 defects in measured volume. (in the surface resonator).
Conventional ESR resonator (10K): Surface resonator (10K):
Sample
Surface resonator
Imaging results
2D ESR image for 10 µm thick layer of phosphorous doped 28Si, taken at 10K.
Future plans
Smaller resonators.
Superconducting surface resonators.
Higher frequencies.
Magnetic Resonance Group members:
Prof. Aharon BlankDr. Ygal Twig
Dr. Lazar ShtirbergAlon PlattnerMichael LevitAlex katchlisKsenia SirotaOmri Arbiv
Gubrail ShakkourRami MaymonMada Hashem
Itai KatzHelen Wolfson
Thank you for your attention