Simple molecules as benchmark systems for molecular electronics

Transcription

1 Simple molecules as benchmark systems for molecular electronics 1

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

3 Early proposal: a molecular diode L-B techniek A. Aviram & M. A. Ratner, Chem. Phys. Lett Lett. 29:277 (1974) Metzger et al., J. Am. Chem. Soc. 119: (1997) Al 1LB C 16 H 33 Q-3CNQ Al (Hexadecylquinolinium Tricyanoquinodimethanide) 3

4 Two-state molecules: memory cells Stanley Williams and his group, Hewlett-Packard Laboratories Palo Alto, California, USA 4

5 Thiol-coupled individual molecules M.A. Reed, C. Zhou, C.J. Muller, T.P. Burgin, and J.M. Tour, Science 278, 252 (1997) J. Reichert et al., Phys. Rev. Lett. 88, (2002) J. Reichert et al., Appl. Phys. Lett. 82, 4137 (2003). See also Kergueris et al. Phys. Rev. B 59, (1999). 5

6 Mechanically Controllable Break Junction 6

7 Mechanically Controllable Break Junction 7

8 Conductance (2e 2 /h) Gold, 4.2 K Piezo-voltage (V) 8

9 Conductance histogram for Au 50 # points (x 10 3 ) G [2e 2 /h] 9

10 Conductance curve for Pt Conductance (2e 2 /h) Pt Piezovoltage (V) 10

11 Conductance histogram for Pt 0.8 Number of counts Pt Conductance (2e 2 /h) 11

12 Conductance curve for Pt/H 2 5 Conductance (2e 2 /h) Pt/H 2 Pt Piezovoltage (V) 12

13 Conductance histogram for Pt/H Number of counts Pt/H 2 Pt Bias voltage 140 mv Conductance (2e 2 /h) 13

14 Principle of point contact spectroscopy E ev G decreases for ev > ħω k 14

15 0,95 Point contact spectrum for Pt/H2 Pt/H 2 di/dv (2e 2 /h) 0,94 0,93 0,92 Modulation: 1 mv, 7 khz Recording time: 10 s Temperature: 4.2 K 0,04 dg/dv (a.u.) 0,02 0,00-0, mv 63.5 mv -0, Bias voltage (mv) 15

16 Counts Isotope shift 9 Pt + HD Pt + D 2 Pt + H Counts Vibration mode energy [mev] Pt-H2 not scaled Pt-D2 by 2 Pt-HD by (3/2) Vibration mode energy [mev] 16

17 More frequencies and stretching dependence 0,96 0,94 0,92 0,0 PtH 2 (no. 13) Energy (mev) 1,03 1,02 1,01 1,00 0,0-0, d 2 I/dV 2 (a.u.) di/dv (G0 ) d 2 I/dV 2 (a.u.) di/dv (G0 ) Energy (mev) 0,96 0,94 0,92 0,0 PtH 2 (no. 14, stretched no.13) Energy (mev) 0,96 0,94 0,1 0,92 0,0-0, d 2 I/dV 2 (a.u.) di/dv (G0 ) d 2 I/dV 2 (a.u.) di/dv (G0 ) Energy (mev)

18 Vibration modes of a Pt H 2 Pt bridge Count 50 PtH Energy (mev) 18

19 New local density calculations D. Djukic, K.S.Thygesen, K.W. Jacobsen, et al., Phys. Rev. B, in print 19

20 Vibration modes for Deuterium, PtDPt D 2 2 Pt d 2 I/dV 2 (a.u.) di/dv (G 0 ) 0,98 0,96 0,0 PtD 2-0, Energy (mev) 20

21 Vibration modes for Deuterium, PtDPt D 2 2 Pt d 2 I/dV 2 (a.u) di/dv (G 0 ) 1,04 1,02 1,00 0,98 0,1 0,0-0,1 same as stretched by 0.05 nm Energy (mev) 21

22 Comparison H 2 and D PtH 2 60 Count Count PtD Energy (mev) Energy (mev) 22

23 Scaling of the modes by m PtD 2 PtD 2 PtD 2 PtH 2 PtH 2 2 Count Energy (mev) 23

24 Scaling of the modes by m Count 70 PtD 2 PtD 2 60 PtD 2 PtHD 50 PtHD PtH 2 40 PtH / Energy (mev) 24

25 Shot noise time frequency S I = 2eI 25 noise power current

26 Multiple channels and finite temperature General expression: S = In the limit of k B T 0: I 2eV 2e h And in the limit for all T n «1: 2 ev coth 2kBT Tn (1 Tn ) + 4k n 2 2e S I = 2eV Tn (1 Tn ) h S I = 2 evg = 2eI n B T 2e h 2 T 2 n n V.A. Khlus, Sov. Phys. JETP 66 (1987) 592 G.B. Lesovik, JETP Lett. 49 (1989) 592 M. Büttiker, Phys. Rev. Lett. 65 (1990) 2901 Review: Ya. M. Blanter and M. Büttiker, Phys. Rep. 336 (2000)

27 Transmission dependence of noise Shot noise spectral intensity: For fermions: S I Zero temperature: and n 2 2 { 0,1} n = n S n ( n ) n I 1 n 2 ( T ) n = T SI T 1 27

28 Experimental technique 28

29 Shot noise on Pt-D 2 junctions Total noise (V 2 /Hz) 1E-17 PtD 2 0A 0.1µΑ 0.2µΑ 0.3µΑ 0.4µΑ 0.5µΑ 0.6µΑ 0.7µΑ 0.8µΑ 0.9µΑ Shotnoise (A 2 /Hz) 1E-25 1E-26 1E-27 1z 2z 3z 4z 5z 6z 8z *10-7 A PtD 2 1E-18 3x10 3 4x105x10 3 6x10 3 7x10 3 8x10 3 9x10 3 2x10 4 3x10 4 4x10 4 5x106x10 4 7x10 4 8x10 4 f(hz) 1E f(hz) B 4,0 3,5 Y Axis Title Data: 0s_B Model: user3 Weighting: y No weighting Chi^2/DoF = E-39 R^2 = a 3.668E-18 ±9.52E-21 b E-5 ±4.2586E-7 c E-5 ±5.1872E-7 Shot noise (10-26 A 2 /Hz) 3,0 2,5 2,0 1,5 1,0 PtD 2 B=0.71 F= T 1 =0.999 T 2 =0.021 T= E-18 0, X Axis Title 0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 Bias current (µa) 29

30 A test case for model calculations Y. Garcia, J.J. Palacios, et al., Phys. Rev. B 69, (2004) Conduction by bonding orbitals. G = 0.2 G 0. 30

31 A test case for model calculations K. Thygesen and K.W. Jacobsen, Phys. Rev. Lett. 94 (2005) Conduction by antibonding orbitals. G = 1.0 G 0 31

32 Molecules with higher condensation points pump molecules 1.5 m 4.2 K 0-30 V Boiling points: C 2 H 2 (188 K) CO (82.4 K) H 2 (20 K) 32

33 CO and Pt (preliminary) Counts Pt Pt-CO Conductance (2e 2 /h) d 2 I/dV 2 (a.u.) di/dv (2e 2 /h) 0,98 0,96 0,94 0,1 0,0-0, Energy (mev) Pt-CO d 2 I/dV 2 (a.u.) di/dv (2e 2 /h) 0,98 0,96 0,94 0,92 0,90 0,2 0,0-0, Energy (mev) Pt-CO d 2 I/dV 2 (a.u.) di/dv (2e 2 /h) 0,98 0,96 0,94 0,92 0,90 0,2 0,0-0,2 Pt-CO Energy (mev)

34 C 2 H 2 molecule between Pt leads (preliminary) Count (a.u.) Pt-C 2 H 2 d 2 I/dV 2 (a.u.) di/dv (2e 2 /h) Conductance (2e 2 /h) Energy (mev) D. Djukic et al., to be published 34

35 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 35

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37 Conductance fluctuations: 3 examples Au G (V) = di/dv (2e 2 /h) Bias voltage (mv) 37

38 Principle of conductance fluctuations in ballistic contacts Diffusive Bank Ballistic Point Contact Diffusive Bank γ r tat' t tar' rat 38

39 RMS fluctuations measured for Au σ GV [G o /V] Gold Au G [2e 2 /h] 39

40 Conductance fluctuations Counts T = 0.97 (1) 3 2 σ GV (a.u.) Conductance (2e 2 /h) 0 R.H.M. Smit et al., Nature 419, 906 (2002) 40