1. 1 Experimental characterization of simple single-molecule junctions

2. 2 In collaboration with... Leiden: Marc van Hemert IBM Yorktown Heights: Norton Lang Technical University of Denmark: Kristian Thygesen, Karsten Jacobsen. Kamerlingh Onnes Laboratory, Leiden University Darko Djukic Yves Noat Roel Smit Carlos Untiedt & JvR

3. 3 Mechanically Controllable Break Junction

4. 4

5. 5

6. 6 Conductance histogram for Au

7. 7 Conductance curve for Pt

8. 8 Conductance histogram for Pt

9. 9 Conductance curve for Pt/H 2

10. 10 Conductance histogram for Pt/H 2 Bias voltage 140 mV

11. 11 G decreases for eV > ħω Principle of point contact spectroscopy

12. 12 Point contact spectrum for Pt/H 2 Modulation: 1 mV, 7 kHz Recording time: 10 s Temperature: 4.2 K

13. 13 Isotope shift

14. 14 Conductance fluctuations: 3 examples Au

15. 15 Principle of conductance fluctuations in ballistic contacts

16. 16 RMS fluctuations measured for Au Au Gold

17. 17 Conductance fluctuations T = 0.97 (1) Smit et al., Nature 419, 906 (2002)

18. 18 More frequencies and stretching dependence

19. 19 K.S.Thygesen and K.W. Jacobsen (unpublished) New local density calculations

20. 20 Vibration modes of a Pt – H 2 – Pt bridge

21. 21 PtD 2 Vibration modes for Deuterium, Pt–D 2 –Pt

22. 22 PtD 2 Vibration modes for Deuterium, Pt–D 2 –Pt

23. 23 PtD 2 K.S.Thygesen and K.W. Jacobsen (unpublished)

24. 24 Comparison H 2 and D 2

25. 25 Scaling of the modes by √m  2  

26. 26 Scaling of the modes by √m  2    3/2  

27. 27 A test case for model calculations J. Kuipers and M.C. van Hemert, unpublished Conduction by antibonding orbitals. G = 0.9 G 0. N. Lang (Nature 419 (2002) 906). M.C. van Hemert, (Nature 419 (2002) 906)

28. 28 A test case for model calculations Y. Garcia, J.J. Palacios, et al., cond-mat/0310098 Conduction by bonding orbitals. ΔE=23eV. G = 0.2 G 0.

29. 29 A test case for model calculations J. Heurich, F. Pauli, J.C. Cuevas, W. Wenzel and G. Schön, Nanotechnology 14 (2003) R29. Conduction by bonding orbitals. ΔE = 24eV. G = 0.86 G 0

30. 30 A test case for model calculations K. Thygesen and K.W. Jacobsen, unpublished. Conduction by antibonding orbitals. ΔE = 10-13 eV. G = 1.0 G 0

31. 31 CO and Pt (preliminary)

32. 32 Conclusions Molecular hydrogen forms a nearly ideal conductor when placed between Pt electrodes, despite the closed-shell character of the free molecule. Single-molecule junctions can be characterized by the vibration modes, their stretching dependence, by the conductance and by the number of conduction channels. Hydrogen forms a good test-case for model calculations. More work on larger organic molecules … Universiteit Leiden

33. 33 Switching behavior for HD

34. 34 PtHD puzzle Switching during stretching