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Molecular Spintronics with SAMs: A Solution to Compatibility Issues
- 1. MOLECULAR SPINTRONICS with SAMs e- Instituto de Ciencia Molecular · Universitat de València (Spain) Unité Mixte de Physique CNRS/Thales · Palaiseau (France) Sergio.Tatay@uv.es 1
- 2. 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
- 3. e e e e e e e e The BASIC ELECTRONIC DEVICE V e e e e e e e e CONDUCTING CONDUCTING 3
- 4. e e e e e e e e The BASIC SPINTRONIC DEVICE (I) Ferromagnetic electrode = spin polarizer Spintronic devices = spin polarizer-analizer V CONDUCTING MAGNETIC CONDUCTING MAGNETIC e e e e e e e e 4 The BASIC SPINTRONIC DEVICE (I)
- 5. The BASIC SPINTRONIC DEVICE (II) Spintronic devices = spin polarizer-analizer Two configurations are possible V e V e e e e 5
- 6. The BASIC SPINTRONIC DEVICE (III) Two configurations are possible We can switch between them using and external magnetic field Magnetic Field Resistance Magnetic Field 6 V e e e e V e
- 7. 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
- 8. SPINTRONICS WHAT FOR? 8 + NVEMag.Sensor APPLICATIONS GMR effect (2007 Nobel prize) already in all your hard drives… FreescaleMRAM ToshibaHD ToshibaHD Thales, IBM, Intel, Seagate … SPIN DEPENDENT TRANSPORT NANOSTRUCTURATION
- 9. 9 WHY?
- 10. 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. 11 AT THE INTERFACE InorganicMetal EF V. B. C. B.
- 12. 12 MOLECULAR HIBRIDIZTION ϵ0 EF Γ ϵeff At the interface Isolated/bulk LUMO HOMO MoleculeMetal
- 13. Molecule ΔE↓ ΔE↑ Γ↑ LUMO 2nd Molecular layer1rst 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
- 14. 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. 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
- 16. -‐0,6 -‐0,4 -‐0,2 0,0 0,2 0,4 0,6 0 50 100 150 200 250 300 350 L S MO /A lq3 /C o Magnetoresistance (%) A pplied magnetic field (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 Magnetoresistance (%) A pplied magnetic field (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
- 17. 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. 18 But, How to control SPINTERFACES? Problem dissolved problem solved
- 19. 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. 20 SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM Interacts with the surface Defined structure HEAD BODY ANCHORING SOLUTION
- 21. 21 SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM Interacts with the surface Defined structure Highly Tunable
- 22. 22 SELF-ASSEMBLED MONOLAYERS (SAMs) THE IDEAL SYSTEM Interacts with the surface Defined structure Highly tunable Controllable thickness nm
- 23. OBJECTIVE 23 ADVANTAGES SAMs as SPINTRONIC BARRIERS MAGNETIC MAGNETIC • Tunable interaction with the surface • Defined structure • Controlable thickness
- 24. 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
- 25. 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.
- 26. 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
- 27. 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)
- 28. CHARACTERIZATION (I) CONTACT ANGLE 28 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
- 29. 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
- 30. 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
- 31. 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
- 32. 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)
- 33. 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
- 34. AFM-NANO LITHOGRAPHY 34 An AFM tip is used to notch a hole into a previously deposited mask
- 35. AFM-NANO LITHOGRAPHY 35 An AFM tip is used to notch a hole into a previously deposited mask
- 36. AFM-NANO LITHOGRAPHY 36 An AFM tip is used to notch a hole into a previously deposited mask
- 37. AFM-NANO LITHOGRAPHY 37 An AFM tip is used to notch a hole into a previously deposited mask
- 38. AFM-NANO LITHOGRAPHY 38 An AFM tip is used to notch a hole into a previously deposited mask
- 39. 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
- 40. 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
- 41. 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)
- 42. MAGNETO-ELECTRONIC CHARACTERIZATION (I) LSMO Co 42 C12P Clear TMR signals Galbiati, Tatay et al. Adv. Mater. 24 (2012) 6429 (CNRS Thales)
- 43. 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
- 44. 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)
- 45. 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. 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