Spring College on Computational Nanoscience May Electronics and Mechanics of Single Molecule Circuits

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1 Spring College on Computational Nanoscience May 2010 Electronics and Mechanics of Single Molecule Circuits Latha VENKATARAMAN Dept. of Applied Physics, Columbia University New York, NY USA

2 Electronics and Mechanics of Single Molecule Circuits Latha Venkataraman Dept. of Applied Physics Columbia University New York, NY May. 26, ICTP, Italy

3 The Future of Electronics Moore s Law: the number of transistors on an integrated circuit doubles every ~18 months 2006 Dual-Core Intel Itanium 2: >1.7 billion transistors 1974 Intel 8080: 6000 transistors From

4 Changes in the Transistor: From Bell Labs, 1947 Brattain, Bardeen, Shockley Measured ~ hih high Intel: 2006 Itanium-2 chip with 220 million transistors

5 Molecules as Components of Circuits p n V I V The construction of a very simple electronic device, a rectifier. based on the use of a single organic molecule is discussed. Cl OMe V

6 Anatomy of a Single Molecule Device V I molecule So What are these Alligators?

7 Anatomy of a Single Molecule Device V I metal contact molecule metal contact chemical link group

8 Where is the Experimental Challenge? E-beam lithography A biphenyl is ~7Å The gap is 4 nm Image from S. Wind metal contact molecule metal contact V I Key Experimental Issues: Reproducibility Single Molecule Signature

9 Anatomy of a Single Molecule Device chemical link group E F metal contact LUMO t HOMO E F molecule V I Transmissio on HOMO metal contact E F Level Alignment? Level Coupling? Bias dependence? LUMO Energy How can we create such single molecule devices and measure transport? What are key parameters that control transport? How can we get transport functionality from chemistry?

10 Some Major Accomplishments Cl OMe 1974 V 1997 First demonstration of a molecular junction? Reed & Tour Science 1997

11 Outline 1. Experimental Method 2. Structure-Conductance Relations 3. Conductance and Mechanics 4. Switching in Pyridines

Experimental Method STM based mechanically

Isolation Substrate Conductance (G 0 10 0 10 1

and acoustic isolation Low voltage noise for

Advantages: Statistics Same platform for

12 Experimental Method STM based mechanically controlled break junction Tip Piezo Vibration Isolation Substrate Conductance (G Elongation (Å Key Points: Good vibration and acoustic isolation Low voltage noise for piezo Clean substrate & high purity solvents Advantages: Statistics Same platform for different molecules Variable Environment Based on Xu & Tao, Science 2003

13 Breaking A Gold Contact Landauer formalism: G = G 0 t i where G o = 2e 2 /h 5 25 mv bias Au single atom chain has only 1 channel Au 6s Co onductance (G Single Trace At E F transmission probability is ~ 1 Tip From H. Ohnishi et al. Nature (1998 Displacement (nm Sample

14 Some Numbers A single atom contact has: G o = 2e 2 /h = 77.5 S R 0 = 1/G 0 = 12.9 k At 25 mv: 5 25 mv bias I = 1.9 A Co onductance (G Single Trace The current density through h the single atom is : J= A/m 2 Number of electrons per second: Displacement (nm /second

15 Data Analysis Conductance peaks visible at multiples of G =2e o 2 /h Histogram of of traces 5 25 mv bias Co onductance (G ( Single Trace Co onductance Counts (G Displacement (nm Conductance Counts (G 0

16 Data on a Log Scale Conductance peaks visible at multiples of G =2e o 2 /h Co onductance (G Single Trace mv bias Tunneling Displacement (nm Counts Histogram of 1000 traces Conductance (G 0 NOTE: These are linear binned histograms shown on a log-log scale

17 Adding Thiolated Molecules (Ulrich et al, J. Phys. Chem. B 2006 Histogram of 3000 consecutive traces 1 H S SH Au HS SH Conductanc ce (G Coun nts Displacement (nm B 1,4 Benzenedithiol n Conductance (G 0 Steps visible over large conductance range.

different conductance Look for alternate links G = 7 10-5 G 0 G = 2 10-8 G 0

18 Thiols Links: Not Reproducible Conductance depends on geometric details Thiols bind to hollow, bridge, and atop site Each configuration has different conductance Look for alternate links G = G 0 G = G 0 (H. Basch, Ratner et al., Nanoletters 2005 (D. Kruger, H. Fuchs, Parrinello et al, PRL 2002

19 Amines (NH 2 : An Ideal Link (L. Venkataraman et al, Nano Letters 2006 Histogram of consecutive traces 10 0 Au H 2 N NH 2 Conductanc ce (G Coun nts Displacement (nm Conductance (G 0 With 1,4 Benzenediamine, steps are limited over a narrow conductance range.

20 Amines (NH 2 : An Ideal Link (L. Venkataraman et al, Nano Letters 2006 Histogram of consecutive traces 10 0 Au H 2 N NH 2 Conductanc ce (G Coun nts Lorentzian Fit Peak 6.4 x 10-3 G 0 Width ~ 40% Displacement (nm Conductance (G 0 With 1,4 Benzenediamine, steps are limited over a narrow conductance range. 0

Why Do Amines Work? Amine s bind preferentially to under-coordinated Au N N N N N N N N N N N N N N N N N N Amines do not form stable SAM s on Au(111 Amines are used to passivate Au nano-particles.

21 Why Do Amines Work? Amine s bind preferentially to under-coordinated Au N N N N N N N N N N N N N N N N N N Amines do not form stable SAM s on Au(111 Amines are used to passivate Au nano-particles. Details in: 1. Quek et al Nano Letters Li & Kosov, PRB Kamenetska et al, PRL 2009 E NH 3 lone pair Au s Binding Energy ~ 0.7 ev Au-N Bond length ~2.3 Å (DFT in GGA approximation on Au d(3z 2 r 2 Donor acceptor is formed between N-lone pair and Au

22 Outline 1. Experimental Method 2. Structure-Conductance Relations 3. Conductance and Mechanics 4. Switching in Pyridines

9 8 7 6 5 4 3 2 10-7 10-6 10-5 10-4 10-3

23 Conductance of Alkanes (L.Venkataraman et al, Nano Letters 2006, M. Hybertsen et al, J. Phys. Cond. Matter H 2 N n NH 2 Counts Alkane with 7 Carbon atoms and Amine groups on the two ends N = Conductance (G 0 Data offset vertically for clarity

24 Conductance vs Length Counts N H 2 n NH 2 N = Conductance (G 0 Data offset vertically for clarity red Condu uctance (G 0 Measu E F Alkanes decay 0.91/Me 8 LUMO T HOMO G e L E F E HOMO 12 N-N Length (A Direct evidence for nonresonant tunneling (L.Venkataraman et al, Nano Letters 2006, M. Hybertsen et al, J. Phys. Cond. Matter E F

25 Conductance of Polyphenyls N H 2 n NH 2 N: Phenyl Chains Attempted 1 H 2 N NH 2 Counts 2 H 2 N NH 2 N= H 2 N NH Conductance (G 0 Data offset vertically for clarity

26 Conductance vs Length Counts N H 2 N=3 2 1 n NH Conductance (G 0 Data offset vertically for clarity red Condu uctance (G 0 Measu Alkanes decay 0.91/Me 8 Phenyls decay 1.7/Ph 12 N-N Length (A 16 Conjugated better than saturated We are measuring single molecule conductance.

27 Conductance of Acenes (J. Quinn, F. Foss, M. Hybertsen, L. Venkataraman, R. Breslow, JACS Comm H 2 N NH 2 HOMO-LUMO Gap 10.3 ev 1,4 diaminobenzene Counts H 2 N NH 2 ~ 8.3 ev 2,6 diaminonaphthalene Conductance (G 0 NH 2 H 2 N 2,6 diaminoanthracene ~ 6.9 ev

28 Conductance vs Length (J. Quinn, F. Foss, M. Hybertsen, L. Venkataraman, R. Breslow, JACS Comm ,6 diaminoanthracene NH 2 26diaminonaphthalene 2,6 H 2 N NH 2 H 2 N Counts Deviation from exponential dependence red Condu uctance (G NH 2 H 2 N 14di 1,4 i diaminobenzene Conductance (G 0 Measu N-N Length (A 16

29 What Can We Learn With Amine Links? (L. Venkataraman, J. Klare, M. Hybertsen, C. Nuckolls, M. Steigerwald, Nature 2006 A Study of Biphenyls: Conductance vs Conformation Twist Angle Twist Angle Counts ductance Con Twist Angle ( Conductance (G Twist Angle are from calculations

30 What Can We Learn With Amine Links? (L. Venkataraman, J. Klare, M. Hybertsen, C. Nuckolls, M. Steigerwald, Nature 2006 A Study of Biphenyls: Conductance vs Conformation -3 G0 Cond ductance (10 - Amine Link not shown N Twist Angle, (degrees 6 F F F F 7 F Cl F F F Cl Cl Cl ductance Con Twist Angle ( Cosine square dependence measured

31 Conductance from Tunnel Coupling Amine s bind preferentially to under-coordinated Au E NH 3 lone pair Au s Au d(3z 2 r 2 Binding Energy ~ ev Au-N Bond length ~2.3 Å (DFT in GGA approximation Donor acceptor bond is formed between N-lone pair and Au LUMO t E F E F 2t HOMO

32 Structure-Conductance Relation enzene Scaled The eory (T/T be 10 1 Calculated tunnel coupling vs measured conductance H 2 N H 2 N Cl Cl Cl Cl Cl NH 2 NH 2 H 2 N H2 N NH 2 NH 2 Use an Au 1 cluster to obtain tunnel coupling 2t Trends show that G is roughly the same for all molecules 10-4 H 2 N NH 2 T Scaled Experiment (G/G benzene 41 molecules shown here M. Hybertsen et al, J. Phys. Cond. Matter 2008

2 Displacement 1 nm H 3 C CH P P 3 CH 3 CH 3 Methyl Sulfide

33 Are Amines Special? ( Park, et al, JACS Comm 2007 Conductance Measurements for Alkanes with different Ligands Phosphine (P-(CH 3 2 Conductance (G NH 2 SMe PMe 2 Displacement 1 nm H 3 C CH P P 3 CH 3 CH 3 Methyl Sulfide (S-CH 3 H 3 C CH S S 3 Amine (NH 2 H 2 N NH 2 Donor acceptor bonding can be generalized to a range of link groups

Cond. (G 0 10-1 NH 2 SMe 10-2 PMe 2 10-3 10-4 10-5 0 2 4 6 8 Number of CH2 units

34 Testing Alternate Link Chemistries ( Park, et al, JACS Comm 2007 Conductance Measurements for Alkanes with different Ligands Counts Conductance (10-3 G 0 Cond. (G NH 2 SMe 10-2 PMe Number of CH2 units Donor acceptor bonding can be Donor acceptor bonding can be generalized to a range of link groups

35 Outline 1. Experimental Method 2. Structure-Conductance Relations 3. Conductance and Mechanics 4. Switching in Pyridines

36 What Else Can We Learn? We have focused on the conductance histogram peak position but we can get more information: Conductance step length Probability of seeing a step Electrode separation in a junction And with slight modifications to the instrument: Current-voltage measurements Temperature dependent measurements Bond breaking forces

37 Conductance & Displacement 1,4 Benzenediamine 2D Histogram (10000 traces Conductanc ce (G NH 2 NH Displacement (nm

38 2D Histograms for Alkanediamines Counts N H 2 n NH 2 ( Kamenetska, Koentopp, Hybertsen, L.V. PRL 2009 N = Conductance (G 0 Data offset vertically for clarity G 0 Co onductance ( Conductance (G N=4 0.4 Displacement (nm N= C4 steps are shorter than C6 0.5 C6 steps are more frequent than C4 steps Displacement (nm 0.5

39 Mechanics of Junction Formation Data shows: 1. Junctions with longer molecules can sustain greater elongation 2. Junctions with longer molecules form more frequently 150 Snap-back distance ~.65 nm Snap Back Distance (nm Hypothesis: Junctions form only when molecules are long enough to bridge the gap between the electrodes. For short molecules, this happens less frequently. For molecules longer than ~ 1nm, junctions from in 90% of the measurements.

Junction Elongation Simulations ( Kamenetska, Koentopp,

05 Å steps Top layer of Au held fixed Total energy, force

40 Junction Elongation Simulations ( Kamenetska, Koentopp, Hybertsen, L.V. PRL 2009 DFT-based simulations (Turbomole package 20 atom Au clusters Junction was elongated in 0.05 Å steps Top layer of Au held fixed Total energy, force and transmission was calculated at each step Junction 1: Butanediamine bonded to apex on bottom pyramid and to an adatom on top pyramid

atom on the top Energy (ev -1.2-1.4-1.6-1.

41 Junction Elongation Simulations ( Kamenetska, Koentopp, Hybertsen, L.V. PRL 2009 Junction 2: Butanediamine bonded to apex on bottom and to an edge atom on the top Energy (ev Force (nn G (G N-Au 0 Bo ond (Å Junction Elongation (Å 5.0

42 Outline 1. Experimental Method 2. Structure-Conductance Relations 3. Conductance and Mechanics 4. Switching in Pyridines

0 10-1 10-2 10-3 10-4 1500 1 nm Displacement N One molecule

43 Functionality From a Molecule? Bipyridine: A Variation on the Amine N 0 Con nductance (G nm Displacement N One molecule with two conducting states t Cou unts Conductance (10-3 G 0

44 Are The Two Peaks Due To Pyridine Link? (Kamenetska et al, submitted N N Bipyridine N N Pyridine-Ethylene-Pyridine N N Terpyridine N N Pyridine-Ethane-Pyridine Yes, two conducting states are due to the pyridine link.

45 2D Histograms from Bipyridine Data ( Quek, Kamenetska et al, Nature Nanotechnology 2009 G 0 Cond ductance ( Cond ductance (G High Displacement(nm Low conductance follows high conductance on junction elongation 10-4 Low Displacement (nm

Hypothesis: Two Contact Geometries ( Quek, Kamenetska et

with C-N- Au angle smaller than 180 degrees.

molecular -system system, giving a higher conductance 10 2

1 10 1 10-5 2 4 6 10-4 2 4 6 10-3 2 4 6 10-2 Conductance

46 Hypothesis: Two Contact Geometries ( Quek, Kamenetska et al, Nature Nanotechnology N N Junction forms with C-N- Au angle smaller than 180 degrees. Counts Pull Au is better coupled to the molecular -system system, giving a higher conductance 10 2 On pulling, molecule becomes vertical in the junction Conductance (G 0 Au is not well coupled to the molecular -system. This results in a lower conductance

47 Two Types of Measurements 10 0 Pulling Conductanc ce(g Displacement (nm Pushing Conduct tance(g Displacement (nm

48 Au-Au Separation & Conductance ( Quek, Kamenetska et al, Nature Nanotechnology 2009 Pull Hold Push Pull 10 0 Conducta ance (G High Low Time (s Push-back Distance (Å Pull push pull a molecular junction. Use the pushback distance to correlate Au electrode separation to junction conductance.

length for all molecules These data agree with the hypothesis: High

49 Au-Au Separation & Conductance (Kamenetska et al, submitted N N Pyridine-Ethane-Pyridine Push-back distance correlates with molecule length for all molecules These data agree with the hypothesis: High G-conductance results from tilted geometries, while Low-G junctions have a vertical geometry

50 BiPy Transmission Sensitive to Geometry ( Quek, Kamenetska et al, Nature Nanotechnology Self-energy Corrected Transmission ~ cos( LUMO dominates T(E F Large correction (~ 1 ev Coupling of pi system to Au enhanced w/ angle (w/ modest binding energy cost E - E F (ev Conductance increases by 10x, covers Low G & High G expt l range

Structure-Conductance: 55 Junctions ( Quek, Kamenetska et al, Nature Nanotechnology 2009 1 2 3 4

51 Structure-Conductance: 55 Junctions ( Quek, Kamenetska et al, Nature Nanotechnology Different binding sites, bond angles, etc Experimental Conductance Range High G (5.4x10-4 G 0 Low G (1.6x10-4 G 0

52 Quantitative Comparison: Theory & Exp. ( Quek, Kamenetska et al, Nature Nanotechnology 2009 Theory Low G vertical Experiment Tilted geometries vertical geometries High G Tilted Vertical distance between Au binding sites (Å

53 Mechanically-Controlled Switching High G switching Low G smaller Au-Au separation larger Au-Au separation h l l f l f h l Chemical control of a nanoscale interface via mechanical manipulation: Au-pyridine contact geometry dictates conductance!

54 Reversible, controllable mechanical switching! ( Quek, Kamenetska et al, Nature Nanotechnology 2009 Pull 10-2 Push Pull Hold 0-1 Push ance(g 0 Conduct Hold Displacem ment (nm High G Low G Time (s Toggle between low & high G by mechanical manipulation

55 Summary Amine links provide a bottom-up approach to form single molecule with reproducible characteristics. Amine Isonitrile Log Counts Thiol Conductance (G 0

56 Summary Amine links provide a bottom-up approach to form single molecule with reproducible characteristics. ene heory (T/T benze Scaled T Structure conductance relations can be mapped using Amine-Gold link chemistry Scaled Experiment (G/G benzene

57 Summary Amine links provide a bottom-up approach to form single molecule with reproducible characteristics. Structure conductance relations can be mapped using Amine-Gold link chemistry Electronics and mechanics depend on contact linker as well as molecule length.

58 Summary Amine links provide a bottom-up approach to form single molecule with reproducible characteristics. Structure conductance relations can be mapped using Amine-Gold link chemistry 0 Cond ductance(g Displacement (nm Time (s Electronics and mechanics depend on contact linker as well as molecule length. We can use contact properties to demonstrate single molecule switching.

59 Thanks Funding NSEC NSF/NYSTAR NSF- Career Columbia RISE ACS-Petroleum Research Fund Packard Foundation DOE-EFRC EFRC Chemistry: Applied Physics: Jennifer Klare Masha Kamenetska Young Suk Park Adam Whalley Colin Nuckolls Mike Steigerwald Severin Schneebeli Rachid Skouta Ronald Breslow Michael Frei Jonathan Widawsky Sriharsha Aradhya Valla Fatemi Theory: Mark Hybertsen Jeffrey Neaton Max Koentopp Su Ying Quek Hector Vazquez

arxiv: v1 [cond-mat.mtrl-sci] 16 Jul 2007

arxiv: v1 [cond-mat.mtrl-sci] 16 Jul 2007 Amine-Gold Linked Single-Molecule Junctions: Experiment and Theory arxiv:0707.2091v1 [cond-mat.mtrl-sci] 16 Jul 2007 Su Ying Quek, 1 Latha Venkataraman, 2,3 Hyoung Joon Choi, 4 Steven G. Louie, 1, 5 Mark