P. Grutter

Making Contact to Molecules: Interfacing to the Nanoworld

Peter GrutterPhysics DepartmentMcGill University

NSERC, FCAR, CIAR, McGill, IBM, CIHR, GenomeQuebec, CFI, NanoQuebec

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What is Nanoelectronics?

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What is Electronics?• By electronics we mean the handling of complicated

electrical wave forms for communicating information, probing (such as in radar) and data processing.

• Data processing is the result of one complex stream of information interacting with another.

• This requires non-linear behavior, otherwise information just gets passed on from one place to the other. (Landauer, Science 1968)

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Molecular electronics: the issues

• Contacts• Structure-function

relationship between transport process and molecular structure

• Dissipation

• Crosstalk (interconnects)

• Architecture • I-O with a trillion

processors• Fault tolerance• Manufacturing costs

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Does atomic structure of the contact matter?

YES !

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Does atomic structure of the contact matter?

Mehrez, Wlasenko, et al., Phys. Rev. B 65, 195419 (2002)

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Comparison of Experimental and Modeling Results

Mehrez, Wlasenko, et al., Phys. Rev. B 65, 195419 (2002)

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‘Traditional’: infinite, structureless leads -> periodic boundary conditions.

but: - result depends on lead size!- bias not possible due to periodic boundary condition!

Calculating Conductance

Jellium lead Jellium leadmolecule

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Calculation of electrical transport

)],(),([),(2)( 00 eVEfEfVETdEheVI RRLL

O f t e n o n e a s s u m e s t h a t T i s n o t a f u n c t i o n o f V , i . e . :

)(),( ETVET

a n d s t i c k s a l l t h e V d e p e n d e n c e i n t o t h e F e r m if u n c t i o n f

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ab-initio modelling of electronic transport

lead

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DFT plus non-equilibrium Green’s Functions

J. Taylor, H. Guo , J. Wang, PRB 63, R121104 (2001)

1. Calculate long, perfect lead.Apply external potential V by shifting energy levels -> create electrode data base and get potential right

lead

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2. Solve Poisson equation for middle part (device plus a bit of leads); match wavefunctions and potential as a function of V to leads (use data base) in real space.

3. calculated with non-equilibrium Green’s functions (necessary as this is an open system). This automatically takes care of bound states

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Molecular electronics: the issues

• Contacts• Structure-function

relationship between transport process and molecular structure

• Dissipation

• Crosstalk (interconnects)

• Architecture • I-O with a trillion

processors• Fault tolerance• Manufacturing costs

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Reliable, chemically well defined contacts

Cui et al. Nanotechnology 13, 5 (2002), Science 294, 571 (2001)

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Low-T UHV STM/AFM/FIM

140K, 10-11mbar

quick change between FIM - AFM/STM mode

Stalder, Ph.D. Thesis 1995 Cross et al. PRL 80, 4685 (1998) Schirmeisen et al. NJP 2, 29.1

(2000)

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Field Ion Microscopy

(FIM)

E. Muller, 1950’s

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FIM of W(111) tip

Imaging at 5.0 kV

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FIM of W(111) tip

Imaging at 5.0 kV Manipulating at 6.0 kV

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FIM of W(111) tip

Imaging at 5.0 kV Manipulating at 6.0 kV

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FIM of W(111) tip

Imaging at 5.0 kV Manipulating at 6.0 kV

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Single Au atom on W(111) tip

Imaged at 2.1 KV

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W(111) tip on Au(111)

Cross et al. PRL 80, 4685 (1998)Schirmeisen et al, NJP 2, 29.1 (2000)

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Molecular Dynamics Simulations

U. Landman et al, Science 248, 454 (1990)

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W(111) trimer tip on Au(111)

Ead = 21 eV

= 0.2 nm

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Tip relaxation effects

Hofer, Fisher, Wolkow and Grutter Phys. Rev. Lett. 87, 236104 (2001)

W tip on Au(111) surface

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Tip relaxation effects

Hofer, Fisher, Wolkow and Grutter Phys. Rev. Lett. 87, 236104 (2001)

W tip on Au(111) surface

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F(z) and I(z) of W(111) trimer on Au(111)

Schirmeisen et al, NJP 2, 29.1 (2000)

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Yan Sun,

Anne-Sophie Lucier

Henrik Mortensen

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The samples (measurements in progress)

A) Au(111) 170 nm×170 nm,B) mixture of C6 and C8 thiol

(ratio 6:1) on Au(111) 450nm×450nm

C) C8 thiol, 6nm×6nm D) C8/C8 dithiol 36nm×36 nm.

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Stimulation of Single Ligand-Gated Ion Channels

Natural Process:Synaptic Transmission

Goal: To study channel gating kinetics and binding forces, while maintaining precise control of agonist location.

Experiment: Ligand-functionalized AFM tip

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N. Cameron, B. Lennox (McGill)

Tethering Scheme:GABA v.s. GABOB

• Is it possible to tether a molecule of GABA without destroying its functionality?

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Tethering Scheme: Polymer Linker

Au -S-(CH2)12-(O-CH2-CH2)23-O-GABOB {alkanethiol} {PEO}

Colloid simulates the AFM tip

Keeps the colloid complex soluble (?)

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Planar Patch-Clamp Chips• Advanced microstructuring techniques are used to produce apertures in planar glass or quartz substrates.• Low noise recordings have been realized from both artificial lipid bilayers and whole cells.

Fertig et. al. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2001 Oct;64(4-1):040901.

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Loading Rate Dependent Unbinding:

Most probable unbinding force:

• Ligand-receptor dissociation forces and rates depend on the rate at which the bond is ruptured!!!• Distinct binding states can be identified from a force v.s. loading rate plot.

Good review: Evans, E. Annu. Rev. Biophys. Biomol. Struct. 2001. 30:105-28.

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F(z) as a function of

pulling speed

Clausen-Schaumann et al., Current Opinions in Chem. Biol. 4, 524 (2000)Merkel et al., Nature 397, (1999)

Allows the determination ofenergy barriers and thus is a direct measure of the energy landscape in conformational space.

Evans, Annu. Rev. Biophys. Biomol. Struct., 30, 105 (2001)

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Summary

• Tools, both experimental and theoretical, drive our capabilities to understand the nanoworld!

• We develop and apply SPM techniques to interface to:

molecules and neuronsin order to understand

structure - property relationships

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Supported by NSERC, FCAR, CIAR, NanoQuebecCFI, IBM, GenomeQuebec, CIHR McGill Dawson Scholarship

14 graduate students, 6 post doctoral fellows