Molecular Spintronics with SAMs

MOLECULAR SPINTRONICS with SAMs

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Instituto de Ciencia Molecular · Universitat de València (Spain) Unité Mixte de Physique CNRS/Thales · Palaiseau (France)

Sergio.Tatay@uv.es

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A MULTIDISCIPLINAR AREA

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MOLECULAR Science Institute University of Valencia

Paterna (SPAIN)

Unité Mixte de PHYSIQUE CNRS/Thales Palaiseau (France)

PhD Michele Mattera

PhD Clément Barraud

Marta Galbiati Sophie Delprat

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The BASIC ELECTRONIC DEVICE

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CONDUCTING

CONDUCTING

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The BASIC SPINTRONIC DEVICE (I) Ferromagnetic electrode = spin polarizer

Spintronic devices = spin polarizer-analizer

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CONDUCTING MAGNETIC

CONDUCTING MAGNETIC

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The BASIC SPINTRONIC DEVICE (I)

The BASIC SPINTRONIC DEVICE (II) Spintronic devices = spin polarizer-analizer

Two configurations are possible

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The BASIC SPINTRONIC DEVICE (III) Two configurations are possible

We can switch between them using and external magnetic field

Magnetic Field

Resi

stan

ce

Magnetic Field

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Ve

ee

e V e

The BASIC SPINTRONIC DEVICE (IV) Two configurations are possible

We can switch between them

Magnetic Field

MR

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MAGNETORESISTANCE

MR is proportional to de spin polarization of the electrodes 0

SPINTRONICS WHAT FOR?

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+

NVE M

ag. S

enso

r

APPLICATIONS

GMR effect (2007 Nobel prize) already in all your hard drives…

Free

scal

e M

RAM

Tosh

iba

HD

Tosh

iba

HD Thales,

IBM, Intel,

Seagate …

SPIN DEPENDENT TRANSPORT NANOSTRUCTURATION

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WHY?

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MOLECULES as SPINTRONIC BARRIERS

• Long spin life-time

• Plastic compatibility and low price

Barraud et al. Appl. Phys. Lett. 96 (2010) 072502 (CNRS Thales)

Is that all?

MAIN ADVANTAGES

B. Dlubak et al. Nat. Phys. (2012) 587 (CNRS Thales)

lsf ≈ 300 µm

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AT THE INTERFACE

Inorganic Metal

EF

V. B.

C. B.

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MOLECULAR HIBRIDIZTION

ϵ0

EF

Γ ϵeff

At the interface Isolated/bulk

LUMO

HOMO

Molecule Metal

Molecule

ΔE↓ ΔE↑

Γ↑ LUMO

2nd Molecular layer 1rst molecular layer Isolated / bulk

Γ↓

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SPIN DEPENDENT HYBRIDIZATION (I)

FM Metal

Spinterface

EF

ϵ0

Galbiati, Tatay et al. MRS Bull. (2014) In Press (CNRS Thales)

Spinterface “effective” electrode = metal + 1st interfacial molecular state

FM metal Molecule discrete level

EF

SPIN DEPENDENT HYBRIDIZATION (III)

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Spinterface “effective” electrode = metal + 1st interfacial molecular state

Γ >> ΔE (Strong Interaction) Γ << ΔE (Weak Interaction)

Pint = - PFM

FM metal

EF

Molecule discrete level

Pint > PFM

Spin polarization inversion Spin polarization enhancement

The spin polarization at the new interface depends on the strength of the coupling

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MOLECULES as SPINTRONIC BARRIERS

• Long spin life-time

• Plastic compatibility and low price

MAIN ADVANTAGES

BEYOND INORGANICS

Interface plays a key role in spin injection It can be tailored by molecules

• Chemically engineered spintronic properties

-­‐0,6 -­‐0,4 -­‐0,2 0,0 0,2 0,4 0,60

50

100

150

200

250

300

350 L S MO /A lq3/C o

Mag

netoresistan

ce  (%)

A pplied  magnetic  fie ld  (T )

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Γ >> ΔE Γ << ΔE

MOLECULES as SPINTRONIC BARRIERS SPIN DEPENDENT HYBRIDIZTION

-­‐1,0 -­‐0,5 0,0 0,5 1,0-­‐35

-­‐30

-­‐25

-­‐20

-­‐15

-­‐10

-­‐5

0

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Mag

netoresistan

ce  (%)

A pplied  magnetic  fie ld  (T )

C o/C oP c/C o

EF

Co CoPc

Bottom interface

Pint = - PFM

2K 2K

Alq3 LSMO

Co

Co

Co CoPc

Spin polarization inversion Spin polarization enhancement

Barraud et al. Manuscript in preparation (CNRS Thales, UMR7504 (Strasbourg))

EF

Co Alq3

Pint > PFM

300K Pint ≈ + PFM

EF

Co Alq3

Bottom interface

EF

Co CoPc

Bottom interface

Pint = - PFM

300K

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Γ << ΔE Decoupled

MOLECULES as SPINTRONIC BARRIERS SPIN DEPENDENT HYBRIDIZTION

Spin polarization inversion Spin polarization enhancement

Alq3 Co

Co

Galbiati, Tatay et al. Unpublished Results (CNRS Thales)

Co

Co Alq3 Al2O3

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But, How to control

SPINTERFACES?

Problem dissolved problem solved

Cy3

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YES, WE CAN

NO, WE CANNOT

Alq3 MPc

UHV LIMITATIONS: To Alq3 and BEYOND

Mn12O12(CH3COO)16(H2O)4

Ru(bpy)3

Mn12 PEDOT:PSS

CAN WE EVAPORATE?

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SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM

Interacts with the surface

Defined structure

HEAD

BODY

ANCHORING

SOLUTION

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SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM

Interacts with the surface

Defined structure

Highly Tunable

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SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM

Interacts with the surface

Defined structure

Highly tunable

Controllable thickness

nm

OBJECTIVE

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ADVANTAGES

SAMs as SPINTRONIC BARRIERS

MAGNETIC

MAGNETIC

• Tunable interaction with the surface

• Defined structure

• Controlable thickness

SAMs as SPINTRONIC BARRIERS

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PREVIOUS RESULTS Petta, Slater and Ralph

Phys. Rev. Lett. 93 (2004) 136601 Wang and Richter

Appl. Phys. Lett. 89 (2006) 153105

Ni

Ti

Ni

NANOPORE:10nm

Ni

Co

NANOPORE:10nm

ENCOURAGING Proof of Concept

RESULTS

Why ONLY TWO?

MR

(%)

0

2

OBJECTIVE

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MAGNETIC

MAGNETIC

MAGNETIC

(La,Sr)MnO3

CHALLENGES

• Bottom electrode: COMPATIBLE WITH SAMs WET BENCH CHEMISTRY (La,Sr)MnO3 (LSMO)

OUR Approach SAMs as Sintronic Barriers

Air Stable P = 100%

Epitaxially grown Tc < r.t.

OBJECTIVE

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MAGNETIC

MAGNETIC

MAGNETIC

(La,Sr)MnO3

CHALLENGES

• Bottom electrode: COMPATIBLE WITH SAMs WET BENCH CHEMISTRY

• Top electrode: NO SHORT-CIRCUITS

(La,Sr)MnO3 (LSMO)

NANOCONTACTS

OUR Approach SAMs as Sintronic Barriers

Co, Ni...

(La,Sr)MnO3

The FUNCTIONALIZATION of LSMO

Epitaxially grown

(La2/3Sr1/3)MnO3 (LSMO) is a inorganic oxide of the perovskite

family (ABO3)

Surfactant

Z

OLa/Sr Mn

Substrate

SrTiO3 (STO)

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n = 1 to 4

Alkylphosphonic acid Dodecylphosphonic acid (C12P)

Octadecylphosphonic acid (C18P)

Dilute solutions of alkylphosphonic acid in polar solvents

Anchoring: Phosphonic acid (PO3H2) Body: Alkyl chain (CH2)

Head: Methyl group (CH3)

CHARACTERIZATION (I) CONTACT ANGLE

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Water Contact Angle

CA < 80

90 < CA < 100

CA > 100

Contact Angle

Contact Angle (Adv/Rec/Hist)

C18PO3H2 = 112/99/13 C12PO3H2 = 108/82/26

C12P

C18P

•  Good coverage

CHARACTERIZATION (II)

AFM ▪ Roughness comparable to that of the bare substrate ▪ No island or multilayer growth was observed

C12P 1 µm

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XPS ▪ All the expected elements ▪P-O-H peak not present in O(1s). BI/TRI-DENTATE

C12P

CHARACTERIZATION (III)

ATR-IRRAS

THICKNESS

C18PO3H2 = 2.3 nm (27º) C12PO3H2 = 1.3 nm (43º)

▪ Peak position corresponding to good quality layers

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ELLIPSOMETRY

C12P

C18P

C12PO3H2

▪ Chains are tilted

CHARACTERIZATION (IV)

UPS (col. Kaiserslautern.)

▪ Magnetism is kept after deposition process

▪ Manganese gets sligthly reduced

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XAS/XMCD (col. SOLEIL France)

LSMO

0.50eV

-6.53eV -9.51eV

C12P

LSMO

0.62eV

-6.58eV -9.51eV

C18P

4.9eV 4.9eV

HOMO

HOMO-1

HOMO

HOMO-1

EF EF

Surface dipole

Surface dipole

▪ Small surface dipole

C12P

3.50 eV

LUMO

3.50 eV

LUMO

10 eV 10 eV

TRANSPORT MEAS.

▪ Similar to other well know systems

CHARACTERIZATION (V) SUMMARIZING

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C12P = 1.3 nm C18P= 2.3 nm

41o

28o

Tatay et al. ACS Nano 6 (2012) 8753 (CNRS Thales, UVEG)

But, How to MAKE electrical DEVICES?

Spintronics requires metallic electrodes. Thus SHORT-CIRCUITS are a big issue

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(La,Sr)MnO3

Co, Ni...

(La,Sr)MnO3

Co, Ni…

(La,Sr)MnO3

NANOCONTACS

AFM-NANO LITHOGRAPHY

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An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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30 µm

1 µm

10 nm

30 nm

An AFM tip is used to notch a hole into a previously deposited mask

AFM-NANO LITHOGRAPHY

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30 µm

1 µm

10 nm

30 nm

An AFM tip is used to notch a hole into a previously deposited mask

10 nm

LSMO

Co

ELECTRICAL CHARACTERIZATION

Our devices are not short-circuited

R(Co//LSMO) = 1 kΩ R(Co/SAM//LSMO) = 10 MΩ

LSMO

Co

1.3 nm

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10 nm ●Short-Circuited ●C12P

C12P

Tatay et al. ACS Nano 6 (2012) 8753 (CNRS Thales, UVEG)

MAGNETO-ELECTRONIC CHARACTERIZATION (I)

LSMO

Co

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C12P

Clear TMR signals

Galbiati, Tatay et al. Adv. Mater. 24 (2012) 6429 (CNRS Thales)

MAGNETO-ELECTRONIC CHARACTERIZATION (I)

LSMO

Co

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C12P

Park et al. Phys. Rev. Lett. 81 (1998) 1953

Temperature dependence of TMR mainly driven by LSMO surface polarization

MAGNETO-ELECTRONIC CHARACTERIZATION (II)

LSMO

Co

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C12P

TMR signal is maintained at high voltage

Galbiati, Tatay et al. Adv. Mater. 24 (2012) 6429 (CNRS Thales)

INFLUENCE of the CHAIN LENGTH

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MR dependence on chain length

(first results…)

Exponential increase of the resistance with the chain length

LSMO

Co

Galbiati, Tatay et al. Unpublished Results (CNRS Thales)

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CONCLUSION

but most of the materials with potential for spintronics applications are not compatible with

the standard ultrahigh vacuum techniques

and this can be a PROBLEM

A doubtful or difficult matter requiring a

solution

The Concise Oxford Dictionary (1995)

MOLECULES (and specially SAMs) have a great POTENTIAL for spintronics