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Rui Ten Beek

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  • Experimental characterization of simple single-molecule junctions

  • In collaboration with ...Leiden: Marc van HemertIBM Yorktown Heights: Norton LangTechnical University of Denmark: Kristian Thygesen, Karsten Jacobsen.

    Kamerlingh Onnes Laboratory, Leiden UniversityDarko Djukic Yves Noat Roel Smit Carlos Untiedt & JvR

  • Mechanically Controllable Break Junction

  • Mechanically Controllable Break Junction

  • Conductance histogram for Au

  • Conductance curve for Pt

  • Conductance histogram for Pt

  • Conductance curve for Pt/H2

  • Conductance histogram for Pt/H2Bias voltage 140 mV

  • G decreases for eV > Principle of point contact spectroscopy

  • Point contact spectrum for Pt/H2Modulation: 1 mV, 7 kHzRecording time: 10 sTemperature: 4.2 K

  • Isotope shift

  • Conductance fluctuations: 3 examplesAu

  • Principle of conductance fluctuationsin ballistic contacts

  • RMS fluctuations measured for AuAuGold

  • Conductance fluctuationsT = 0.97 (1)Smit et al., Nature 419, 906 (2002)

  • More frequencies and stretching dependence

  • New local density calculations

  • Vibration modes of a Pt H2 Pt bridge

  • PtD2Vibration modes for Deuterium, PtD2Pt

  • PtD2Vibration modes for Deuterium, PtD2Pt

  • PtD2K.S.Thygesen and K.W. Jacobsen (unpublished)

  • Comparison H2 and D2

  • Scaling of the modes by m

  • Scaling of the modes by m

  • A test case for model calculationsJ. Kuipers and M.C. van Hemert, unpublished Conduction by antibonding orbitals. G = 0.9 G0.N. Lang (Nature 419 (2002) 906) .M.C. van Hemert, (Nature 419 (2002) 906)

  • A test case for model calculationsY. Garcia, J.J. Palacios, et al., cond-mat/0310098Conduction by bonding orbitals. E=23eV.G = 0.2 G0.

  • A test case for model calculationsJ. Heurich, F. Pauli, J.C. Cuevas, W. Wenzel and G. Schn, Nanotechnology 14 (2003) R29.Conduction by bonding orbitals. E = 24eV.G = 0.86 G0

  • A test case for model calculationsK. Thygesen and K.W. Jacobsen, unpublished.Conduction by antibonding orbitals. E = 10-13 eV.G = 1.0 G0

  • CO and Pt (preliminary)

  • ConclusionsMolecular 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

  • Switching behavior for HD

  • PtHD puzzleSwitching during stretching

    Minute amount of hydrogenExact dosage hard to establish, since it condenses at 4.2 K. Equilibrium pressure is 10-6mbar.

    At low bias voltage lots of weight below 1 G0.Peak at 1 becomes more pronounced for higher bias.Above 200 mV we recover the clean Pt histogram.Attributed to local heating.H is monovalent.Numerical calculation for Pt-H-H-Pt bridge gives G close to oneBinding energy per Pt-H bond is 2.4 eV: strong bond!Back so single curve: select a plateau at 1 G0.So from hw we see a step in conductance

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