Physical Principles of
Nanoelectromechanical Devices
Robert Shekhter
University of Gothenburg, Sweden
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
2/35
Electromechanics and Charge Metrology
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.
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
3/35
Downsizing of Electro-Mechanical
Devices
Macroscopic 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.
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)
Outline
 Why NEMS?
 Fabrication methods
 Actuation and detection methods
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Part 1
Why NEMS?
7/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
MEMS – already a mature technology
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.
8/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
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.
9/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
New Functionality and Possible
Applications of Nanoscale
Electromechanics



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
10/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
11/35
Resonant Mass Sensors
(mass sensing on the level of single molecules)
low M , high w0 , high Q
See review in Nature Nanotech. 4, 445 (2009)
[Roukes’ group (Caltech)]
Sensitivity: ~200 Da
Nature Nanotech. 3, 533 (2008);
Nano Lett. 8, 4342 (2008)
200 Dalton=3.6 10-22 g
dMmin ≈ M/Q
Roukes’ group (Caltech): Nature
Nanotechn 4, 445 2009 (Roukes)
Sensitivity: 100 zepto-grams
K.L.Ekinci et al. APL 64, 4469 (2004)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Biomolecular Recognition
Surface stress changes the nanomechanical
response of cantilevers. Bending of cantilevers
detected by an optical deflection technique.
J. Fritz et al., Science 288, 316 (2000)
12/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
13/35
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
-5 eHz-1/2
• ultimate sens. (300 K): 2 10
•
A.N. Cleland and M.L. Roukes, Nature 392, 160 (1998)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Detection of Nanomechanical
Displacements
Tuning band gap with strain
PRL 90, 156401 (McEuen)
Blurring in STM from thermal
vibrations, Nano Lett. 3, 1577
(2003) (Schönenberger, Basel)
14/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
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)
15/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
16/35
bias volatge
Nanomechanical Single-Electron
Transistor
gate voltage
Nature 407, 57 (2000) (P.L. McEuen, Cornell)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
17/35
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)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Nanoelectromechanics of the Breaking
of an Atomic Gold Wire
18/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Part 2
Fabrication methods
19/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
20/35
Top-Down – Semiconducting Suspended
Nanowires
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Bottom-Up – Self-Assembled MetalOrganic 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
21/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
22/35
Molecular Junctions
Methods to fabricate molecular junctions
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
23/35
Basic Characteristics Self-Assembled
Materials
Materials properties
Electrical – heteroconducting
Mechanical - heteroelastic
Electronic properties
Quantum coherence
Coulomb correlations
Electromechanical coupling
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Suspended CNTs
24/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Suspended CNTs
25/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Part 3
Actuation and detection
methods
26/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
27/35
Methods of Actuation and Detection
a)
b)
c)
d)
STM detection
Capacitive actuation and detection
Magnetomotive method
Tunnel spectroscopy and point-contact spectroscopy
of NEM vibrations
a) Mechanically assisted transport of electrons
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
28/35
Different Types of NEM Coupling
C(x)
• Capacitive coupling
• Tunneling coupling
R(x)
• Shuttle coupling
C(x) R(x)
I
• Inductive coupling
Lorentz force
for given I
FL
H .
E
v
Electromotive
force at I = 0
for given v
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
29/35
Electrostatic Actuation and Detection
300 nm
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.
d q  d (CgVg )  CgdVg  Vgd Cg
Non-zero only if beam moves
V. Sazonova et al., Nature 431,
284 (2004)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
30/35
Intrinsic Thermal Vibrations of Single-Wall Carbon
Nanotubes Imaged by a Scanning Electron Microscope
(SEM)
Babic et al., Nano Letters 3, 1577 (2003)
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
31/35
Magnetomotive Actuation and Detection
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Magnetomotive Method: Pt Nanowire
32/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
33/35
Magnetomotive Method: Breaking the
GHz Barrier
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
34/35
Measuring Eigenfrequencies: Phonon
Assisted Tunneling
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
Point Contact Spectroscopy in a H2
Molecule
35/35
Lecture 1: Introduction to nanoelectromechanical systems (NEMS)
36/35
Vibration Modes for Deuterium, Pt-D2-Pt