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MOLECULAR SPINTRONICS with SAMs
e-
Instituto de Ciencia Molecular · Universitat de València (Spain) Unité Mixte de Physique CNRS/Thales · Palaiseau (France)
1
A MULTIDISCIPLINAR AREA
2
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
V
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CONDUCTING
CONDUCTING
3
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The BASIC SPINTRONIC DEVICE (I) Ferromagnetic electrode = spin polarizer
Spintronic devices = spin polarizer-analizer
V
CONDUCTING MAGNETIC
CONDUCTING MAGNETIC
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4
The BASIC SPINTRONIC DEVICE (I)
The BASIC SPINTRONIC DEVICE (II) Spintronic devices = spin polarizer-analizer
Two configurations are possible
V e V
e
e e
e
5
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
6
Ve
ee
e V e
The BASIC SPINTRONIC DEVICE (IV) Two configurations are possible
We can switch between them
Magnetic Field
MR
7
MAGNETORESISTANCE
MR is proportional to de spin polarization of the electrodes 0
SPINTRONICS WHAT FOR?
8
+
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
9
WHY?
10
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
11
AT THE INTERFACE
Inorganic Metal
EF
V. B.
C. B.
12
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↓
13
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)
14
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
15
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 )
16
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
5
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
17
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
18
But, How to control
SPINTERFACES?
Problem dissolved problem solved
Cy3
19
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?
20
SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM
Interacts with the surface
Defined structure
HEAD
BODY
ANCHORING
SOLUTION
21
SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM
Interacts with the surface
Defined structure
Highly Tunable
22
SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM
Interacts with the surface
Defined structure
Highly tunable
Controllable thickness
nm
OBJECTIVE
23
ADVANTAGES
SAMs as SPINTRONIC BARRIERS
MAGNETIC
MAGNETIC
• Tunable interaction with the surface
• Defined structure
• Controlable thickness
SAMs as SPINTRONIC BARRIERS
24
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
25
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
26
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)
27
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
29
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
30
ELLIPSOMETRY
C12P
C18P
C12PO3H2
▪ Chains are tilted
CHARACTERIZATION (IV)
UPS (col. Kaiserslautern.)
▪ Magnetism is kept after deposition process
▪ Manganese gets sligthly reduced
31
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
32
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
33
(La,Sr)MnO3
Co, Ni...
(La,Sr)MnO3
Co, Ni…
(La,Sr)MnO3
NANOCONTACS
AFM-NANO LITHOGRAPHY
34
An AFM tip is used to notch a hole into a previously deposited mask
AFM-NANO LITHOGRAPHY
35
An AFM tip is used to notch a hole into a previously deposited mask
AFM-NANO LITHOGRAPHY
36
An AFM tip is used to notch a hole into a previously deposited mask
AFM-NANO LITHOGRAPHY
37
An AFM tip is used to notch a hole into a previously deposited mask
AFM-NANO LITHOGRAPHY
38
An AFM tip is used to notch a hole into a previously deposited mask
AFM-NANO LITHOGRAPHY
39
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
40
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
41
10 nm ●Short-Circuited ●C12P
C12P
Tatay et al. ACS Nano 6 (2012) 8753 (CNRS Thales, UVEG)
MAGNETO-ELECTRONIC CHARACTERIZATION (I)
LSMO
Co
42
C12P
Clear TMR signals
Galbiati, Tatay et al. Adv. Mater. 24 (2012) 6429 (CNRS Thales)
MAGNETO-ELECTRONIC CHARACTERIZATION (I)
LSMO
Co
43
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
44
C12P
TMR signal is maintained at high voltage
Galbiati, Tatay et al. Adv. Mater. 24 (2012) 6429 (CNRS Thales)
INFLUENCE of the CHAIN LENGTH
45
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)
46
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