Physical Principles of Nanoelectromechanical Devices

Robert Shekhter

University of Gothenburg, Sweden

William Gilbert Born on May 24, 1544, in

Colchester, England Died on Dec. 10, 1603, in London

The electroscope was an early scientific instrument used to detect the presence and magnitude of electric charge on a body.

Electromechanics and Charge Metrology

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Downsizing of Electro-Mechanical DevicesMacroscopic Electromechanical Device

Micro-Electromechanical Accelerometer (Airbag Sensor)

A small integrated circuit with integrated micro mechanical elements, which move in response to rapid deceleration. This motion causes a change in capacitance, which is detected by the electronics on the chip that then sends a signal to fire the airbag.

Nano-Electromechanical Machinery in the Living Cell

Ion channels make it possible for cells to generate and transmit electrical signals, and are the basic molecular building blocks in the nervous system. Rapid transport, ion selectivity, and electrically controlled channel gating are central to their functionality.

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Five-Lecture Course on the Basic Physics of Nanoelectromechanical Devices

• Lecture 1: Introduction to nanoelectromechanical systems (NEMS)

• Lecture 2: Electronics and mechanics on the

nanometer scale• Lecture 3: Mechanically assisted single-electronics• Lecture 4: Quantum nano-electro-mechanics• Lecture 5: Superconducting NEM devices

References

 Book: Andrew N. Cleland, Foundation of Nanomechanics

Springer,2003 (Chapter7,esp.7.1.4, Chapter 8,9);

Reviews: R.Shekhter et al. Low.Tepmp.Phys. 35, 662 (2009);

J.Phys. Cond.Mat. 15, R 441 (2003)

J. Comp.Theor.Nanosc., 4, 860 (2007)

 

Lecture 1: Introduction to nanoelectromechanical systems (NEMS)

Why NEMS? Fabrication methods Actuation and detection methods

Outline

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Part 1Why NEMS?

MEMS applications can be found in the information technology, transport industry, medicine and many other fields totalling more

than1000 million dollars of revenues per year.

MEMS – already a mature technology

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Device applications… Smaller, cheaper, faster, lower power consumption

”Phones of the future”. NEM-devices are in the right frequency range (1-5 GHz) to replace elements in cell phones

Better frequency selectivity (higher Q), lower power consumption

New sensor applications

Needed: High Q, high frequency… and interesting

“cutting edge” physics.

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NEM sensing (sensing of mass, displacements and forces on an atomic scale)

Mechanical control and mechanically assisted transportation of single electrons

Mechanically controllable quantum point contacts

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New Functionality and Possible Applications of Nanoscale

Electromechanics

Resonant Mass Sensors(mass sensing on the level of single molecules)

Roukes’ group (Caltech): Nature Nanotechn 4, 445 2009 (Roukes)Sensitivity: 100 zepto-gramsK.L.Ekinci et al. APL 64, 4469 (2004)

200 Dalton=3.6 10-22 g

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low M , high 0 , high Q

See review in Nature Nanotech. 4, 445 (2009)[Roukes’ group (Caltech)]

Sensitivity: ~200 DaNature Nanotech. 3, 533 (2008);Nano Lett. 8, 4342 (2008)

Mmin ≈ M/Q

Biomolecular RecognitionSurface stress changes the nanomechanical response of cantilevers. Bending of cantilevers detected by an optical deflection technique.

J. Fritz et al., Science 288, 316 (2000)

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MEMS/NEMS Devices as Electrometers

NEMS analogue of Coulomb’s torsional electrometer from 1784. A charge on the gate affects the resonance frequency.

• measured sensitivity (300 K): 0.1eHz-1/2

• ultimate sens. (300 K): 2 10-5 eHz-1/2

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A.N. Cleland and M.L. Roukes, Nature 392, 160 (1998)

Detection of Nanomechanical Displacements

Tuning band gap with strainPRL 90, 156401 (McEuen)

Blurring in STM from thermalvibrations, Nano Lett. 3, 1577(2003) (Schönenberger, Basel)

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Nanomechanical Manipulation (Nanotweezer)

Left: A nanotweezer made of two isolated CNTs is opened and closed by applying a bias voltage.

Top: Optical micrographs showing the sequential process of nano-tweezer manipulation of polystyrene nanoclusters containing fluorescent dye molecules.

P. Kim and C.M. Lieber, Science 286, 2148 (1999)

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Nature 407, 57 (2000) (P.L. McEuen, Cornell)

gate voltage

Nanomechanical Single-Electron Transistor

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Mechanical “Sharpening” of Quantum Point Contact

Top left: Top and side view of a mechanically controlled break junction, with notched wire (1), two fixed counter supports (2), bending beam (3), drops of epoxy adhesive (4) and stacked piezo element (5).

Top right: Electron microscopy image of a gold break junction on SiO2 cantilvers

Right: Sharpening of the contact by mechanical elongation

N. Agrait et al., Phys. Rep. 377, 81 (2003)

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Nanoelectromechanics of the Breaking of an Atomic Gold Wire

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Part 2Fabrication methods

Top-Down – Semiconducting Suspended Nanowires

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Bottom-Up – Self-Assembled Metal-Organic Composites

Molecular manufacturing – a way to design materials on the nanometer scale.

Encapsulated 4 nm Au particles self-assembled into a 2D array supported by a thin film,Anders et al., 1995

Scheme for molecular manufacturing

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Molecular Junctions

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Methods to fabricate molecular junctions

Electrical – heteroconducting

Mechanical - heteroelastic

Quantum coherence

Coulomb correlations

11 12 11/ , 1, 10 10R M R MRC s

Electromechanical coupling

Basic Characteristics Self-Assembled Materials

Materials properties Electronic properties

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Suspended CNTs

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Suspended CNTs

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Part 3Actuation and detection

methods

Methods of Actuation and Detection

a) STM detectionb) Capacitive actuation and detectionc) Magnetomotive methodd) Tunnel spectroscopy and point-contact spectroscopy of NEM vibrationsa) Mechanically assisted transport of electrons

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• Capacitive coupling

• Tunneling coupling

• Shuttle coupling

• Inductive coupling

C(x)

R(x)

C(x) R(x)

Lorentz forcefor given I

Electromotive force at I = 0for given v

I

FL

E

v

H .

Different Types of NEM CouplingLecture 1: Introduction to nanoelectromechanical systems (NEMS) 28/35

Electrostatic Actuation and Detection

V. Sazonova et al., Nature 431, 284 (2004)

Au/Cr electrodes (Au/Cr) are shown in yellow, and the silicon oxide surface in grey. The sides of the trench, typically 1.2–1.5 µm wide and 500 nm deep, are marked with dashed lines. A suspended nanotube can be seen bridging the trench.

300 nm

Non-zero only if beam moves

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( )g g g g g gq C V C V V C

Intrinsic Thermal Vibrations of Single-Wall Carbon Nanotubes Imaged by a Scanning Electron Microscope

(SEM)

Babic et al., Nano Letters 3, 1577 (2003)

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Magnetomotive Actuation and Detection

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Magnetomotive Method: Pt Nanowire

Magnetomotive Method: Breaking the GHz Barrier

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Measuring Eigenfrequencies: Phonon Assisted Tunneling

Point Contact Spectroscopy in a H2 Molecule

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Vibration Modes for Deuterium, Pt-D2-Pt