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Single Molecule Electronics

Single Molecule Electronics. Stuart.Lindsay@asu.edu Arizona Biodesign Institute. Single molecules as a tool for understanding. More Single molecules for better understanding. Photosynthesis and single molecule electronics The ASU-Physics-Chemistry-Engineering-Motorola group:. The Program.

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Single Molecule Electronics

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  1. Single Molecule Electronics Stuart.Lindsay@asu.edu Arizona Biodesign Institute Single molecules as a tool for understanding More Single molecules for better understanding

  2. Photosynthesis and single molecule electronics The ASU-Physics-Chemistry-Engineering-Motorola group:

  3. The Program Measure Single Molecule in well-defined conditions Compare with theory (repeat as needed!) ‘Calibrated’ molecules and contacts for devices Make fixed-gap (useful? T-dep?) devices

  4. The molecule-metal contact problem Many Few-Molecule-Devices have been made but measurements/theories generally do not agree: For example, DNA is: AN INSULATOR (D. Dunlap et al. PNAS 90, 7652, 1993) A SEMICONDUCTOR (D. Porath et al, Nature 403,635, 2000) A CONDUCTOR(Fink and Schoenberger, Nature 398, 407,1999) A SUPERCONDUCTOR (A.Y. Kasumov et al. Science 291, 280, 2001)

  5. Making Single Molecule Junctions • Self-assembly: well defined geometry, contacts • Repeated contact (simpler after answer is known) • Fixed nano-gaps: problem of manufacturability

  6. Self-assembled nanojunction (Science 294, 571, 2001) i

  7. Alkanedithiols – STM Images

  8. NI(V )/N (nA) IV-Curves are integral multiples

  9. Two Models for ‘quantized ‘ data

  10. Histogram of curve multipliers • Find X such that variance from curve to curve is minimized • Over 1000 curves for n=1

  11. IV-Curves of bonded molecules not very stress dependent! Current not stress-dependent – through bond? Bonded F IF(h) Mechanical (Nanotechnology 13 5-14, 2002)

  12. I is closer to theory for bonded molecules Theory Comparison with electrochemistry: Bonded R(C8)=950M K=105s-1, EA=21kJ/m, R(C8)=300M Mechanical

  13. (CH2)10 (CH2)12 More chain lengths give (V) (J. Phys. Chem. B 106 8609-8614, 2002 ) • Also measure Ohmic region carefully to get (0) • Data do NOT agree with theory! I=I0exp[-(v)z]

  14. Clue: I-V doesn’t fit tunneling model well What if the top contact is not so good? Coulomb Blockade?

  15. Coulomb Blockade: Quantized charge transfer R1>>h/2e2  Coulomb Blockade n n

  16. Coulomb Blockade fits (Removes Beta anomaly) C8 C10 C12  r1 = 1M c1 = 0.318aF (from fitting C8) r8 = 128.36M r10 = 252M r12 = 875M (c1, r1 fixed) C8=c10 =c12= 0.085aF (Theory=0.08aF) Good agreement for I, 

  17. Other Measurements - Carotene - Phenylene-ethylenine oligomers -Technique reveals mobility of Au contacts

  18. 32 Å Caroteniod (J. Phys. Chem. B, 107, 6162-6169, 2003) TRANS T/C=4:1 CIS

  19. Simple Tunneling with Coulomb Blockade fits well No ‘free’ parameters a b Measured R1 R2 C1 C2 Trans Cis Carotene easily oxidized but vibronic contribution not dominant

  20. Phenylene-ethylynene Oligomers and Negative Differential Resistance Applied Physics Letters 81 3043-3045 (2002)

  21. 2 Single Molecule NDR 1 1.8G 50G Asymmetry, but molecules NOT oriented? c.f. Reichert et al. PRL 88 2002 Confirms NDR but see non-reversible behavior

  22. Single Molecule Bonding Fluctuations(Science 300 1413, 2002) • “Stochastic switching” reported for • We see the same effect in alkane dithiols • Significant switching with gold sphere attached

  23. Single Molecule Bonding Fluctuations – Property of Au-S • Cannot internal electronic changes • Cannot be top ‘dipping’ into film • Cannot be bond to sphere breaking • Rate increases at annealing temperature • Fluctuations of lower bond 25 60

  24. Conclusions Transport in gold-n-alkane-gold fits ab-initio tunneling calculations well: One molecule, well defined environment. Gold nanocluster introduces Coulomb Blockade Carotene – good agreement with tunneling calculations Phenylene-ethylenine oligomers, confirm NDR. Technique reveals mobility of Au contacts

  25. Break Junctions • - Geometry unknown BUT • Calibration available AND • Most common peak appears to be correct • Much easier than self-assembled junctions • (Xu and Tao, Science 301, 1221-1223 2003)

  26. Single Molecule Conductance from Break Junctions PZT 1 2 3 • Are histogram peaks good data points? • What is the effect of strain?

  27. Gold filaments stretch – maximum force ca 1nN Xu, Xiao, Tao, JACS 2003

  28. Alkanedithiols: N=6: RC6=10.5 MW N=8: RC8=51 MW N=10: RC10=630 MW Major peaks are right peaks

  29. SiO2 Au Au 1um Kubatkin et al. (2003) – (but3 devices/paper) 200nm 200nm 2um 500nm a b Fixed Gaps: EBL, Electrochemistry, Electromigration c d e

  30. 77K 90 Vg=-0.5V Vg=-0.25V 80 Vg=0V 70 Vg=0.25V 60 Vg=0.5V 50 Current(uA) 40 30 20 10 Molecule free molecular transistor 0 -10 -20 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 SDbias(V) Atomic-scale control needed! Our Fixed Gaps: 10% “Success Rate”?

  31. Summary 1: What we think we know • Measurements and theory in good agreement for some (single) molecules • (n-alkanes, carotenes, BDT [Tao, nanolets 4 267]) • Break junctions can give good data and are much simpler

  32. Summary 2: What we don’t know/Can’t do • Single Molecule devices need to be assembled with Atomic Precision! • Fluctuations at room temperature? • Couplings and molecular vs. contact properties? • Redox activity molecules and environment?

  33. ASU PHYSICS Xiadong Cui Otto Sankey John Tomfohr Jun Li Jin He ASU Engineering Nongjian Tao ASU Chemistry Ana Moore Tom Moore Devens Gust Xristo Zarate Alex Primak Yuichi Terazano Motorola Gary Harris Larry Nagahara ACKNOWLEGEMENTS

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