Ekaterina Dikarov (Suhovoy ) Development of high sensitivity, high resolution ESR and its...

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