Long, 140 ns electron spin lifetime in chemically

Long, 140 ns electron spin lifetime in chemically

Long, 140 ns electron spin lifetime in chemically synthesized graphene and related nanostructures and its strong interplay between the surface bound oxygen Blint Nfrdi Lszl Forr Mohammad Choucair Spintronics Spintronics aims to utilize the spin of electrons for new forms of information storage and logic devices.

Key materials parameter: long spin lifetime S long spin diffusion length lS Detrimental: spin orbit coupling one needs light elements magnetic impurities nuclear moments

Spintronics Spintronics aims to utilize the spin of electrons for new forms of information storage and logic devices. Key materials parameter: long spin lifetime S long spin diffusion length lS Detrimental: spin orbit coupling one needs light elements dynamic random-access memory (DRAM) is about 20 ns S Bulk

metal <4 K ~ps semiconductor 100 ns Spintronics Spintronics aims to utilize the spin of electrons for new forms of information storage and logic devices. Key materials parameter: long spin lifetime S

long spin diffusion length lS Detrimental: spin orbit coupling one needs light elements dynamic random-access memory (DRAM) is about 20 ns S Bulk Nano metal <4 K ~ps

semiconductor 100 ns metal 150 ns semiconductor 10 ss Spintronics Spintronics aims to utilize the spin of electrons for new forms of information storage and logic devices. Key materials parameter:

long spin lifetime S long spin diffusion length lS Detrimental: spin orbit coupling one needs light elements dynamic random-access memory (DRAM) is about 20 ns S Bulk Nano metal <4 K

~ps semiconductor 100 ns metal 150 ns semiconductor 10 ss 300 K fs-ps 10-40 ps

1-4 ns Carbon (graphene) Spintronics? High mobility ~104 cm2V-1s-1 Weak spin orbit coupling SI=0 for 12C Theoretical estimates: S =~ss @ 300 K lS= ~300 sm

Carbon (graphene) Spintronics? High mobility ~104 cm2V-1s-1 Weak spin orbit coupling SI=0 for 12C Theoretical estimates: S =~ss @ 300 K lS= ~300 sm M. Peplov Nature 522, 268-269, (2015)

Carbon (graphene) Spintronics? Experimental: S =0.2-2 ns lS= 3-8 sm Optimistic (extrinsic) Metallic, feromagnetic contacts Substrate Ripples Finite size flakes Adatoms functionalization

?!? Theoretical : S =~s s lS= ~300 sm Pessimistic (intrinsic) Broken inversion symmetry Multiple Dirac cones Valley dynamics Carbon (graphene) Spintronics?

Experimental: S =0.2-2 ns lS= 3-8 sm ?!? Theoretical : S =~s s lS= ~300 sm N. Tombros et al. Nature 448, 571-574, (2007) Electron Spin Resonance (ESR)

ESR pros: Contactless (few impurities) No substrate local (inhomogeneity in not a problem) Direct measure of S ESR cons: ~mg sample is required (~10 m2) Solvothermal Graphene ribbons solvothermal synthesis Gram scale production

Catalist free 3D self supporting network of graphene nano ribbons approximates very well the assembly of graphene sheets CESR with S=65 ns (@ T<50 K) M. Choucair et al. Nature Nanotech. 3, 30-33, (2009) B. Nfrdi et al. Carbon 74, 346-351, (2014)

Solvothermal Graphene ribbons M. Choucair et al. Nature Nanotech. 3, 30-33, (2009) B. Nfrdi et al. Carbon 74, 346-351, (2014) CESR at 315 GHz T<50 K CESR + paramagnet S=65 ns Y. Kim et al. PRL, 110, 096602, (2013) B. Nfrdi et al. Carbon 74, 346-351, (2014)

Motional narrowing by conduction electrons T<50 K CESR , paramagnet S=65 ns e- T>50 K CESR + paramagnet coupled eB. Nfrdi et al. Carbon 74, 346-351, (2014)

Graphene Spintronics? There is a graphenic material which Approximates very well the assembly of graphene sheets. Spin lifetime of itinerant electrons in remarkably long 65 ns. It is <10% of the sample volume. But there is hope for graphene spintronics! Why is it so difficult to obtain long spin lifetime? already O2 decreases S significantly O2 sensitivity as grown

treated at 1070 K S=140 ns Factor ~10 increase of S upon heat treatment. The change is completely reversible. Dipole field of O2 B. Nfrdi et al. Chemistry A, 21, 770-777, (2015)

O2 sensitivity Thermogravitometry: 16 wt% is O B. Nfrdi et al. Chemistry A, 21, 770-777, (2015) O2 sensitivity B. Nfrdi et al. Chemistry A, 21, 770-777, (2015) Thank you for your attention!

O2 sensitivity Still not a perfectly homogeneous sample B. Nfrdi et al. unpublished, (2014) Graphene Spintronics? O2 sensitivity XPS:

There is a decrease in O from 16wt.% to <<1%wt. B. Nfrdi et al. Chemistry A, 21, 770-777, (2015) Motional narrowing by conduction electrons B. Nfrdi et al. Carbon 74, 346-351, (2014) Motional narrowing by conduction electrons Pauli= 3.110-7 emu/g (4%)

ne= 1.41010 cm-2 B. Nfrdi et al. Carbon 74, 346-351, (2014) Motional narrowing by conduction electrons Pauli= 3.110-7 emu/g (4%) ne= 1.41010 cm-2 npouddle= 1.51011 cm-2 J. Main et al. N.Phys. 4, 140-148, (2008) B. Nfrdi et al. Carbon 74, 346-351, (2014)

CESR at 315 GHz T<50 K CESR + paramagnet TS=65 ns B. Nfrdi et al. Carbon 74, 346-351, (2014) CESR at 315 GHz T<50 K CESR + paramagnet TS=65 ns

B. Nfrdi et al. Carbon 74, 346-351, (2014) Motional narrowing by conduction electrons Observed an almost perfect Lorentzian shape H=0.043 mTH=0.043 mT =3.71019 spin/g Calculated: re-e = 1.3 nm H=0.043 mTHdip-dip = 0.87 mT Linear broadening with 1.910-4 mT/GHz

B. Nfrdi et al. Carbon 74, 346-351, (2014) ESR Instrumentation 55-420 GHz B0 2 Corrugation Period

4 Corrugation Depth 19.32 mm + +

TE11 + TM11 off-resonance on-resonance = HE11 Propagating Mode

ESR Instrumentation 55-420 GHz Oscillator P1 Mixer 45o Faraday Rotator Local Oscillator Arm

P2 Variable Polarizer Beamsplitter P3 Sample Arm Phase Adjustment Cryostat, Sample

ESR Instrumentation 55-420 GHz

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