Molecular electronics
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Molecular electronics
Biological Systems
Molecular Electronics Devices
Use molecular electronics to study biological systems.
Molecular electronics
Incentives

 Molecules are nano-scale
 Self assembly is achievable
 Very low-power operation
 Highly uniform devices
Quantum Effect Devices

 Building quantum wells using molecules
Electromechanical Devices

 Using mechanical switching of atoms or molecules
Electrochemical Devices

 Chemical interactions to change shape or orientation
Photoactive Devices

 Light frequency changes shape and orientation.
Molecular electronics
Definition
is a field emerging around the premise that it
is possible to build individual molecules that
can perform functions identical to those of
the key components of today’s microcircuits.
Why molecular electronics?
Chip-fabrication
specialists
will
find
it
economically infeasible to continue scaling
down microelectronics.
 stray signals on the chip
 the need to dissipate the heat from so many

closely packed devices
the difficulty of creating the devices in
the first place
Molecular electronics, any better?

Modern technologies can only go so far.

Solution (new development)
 DNA - It is promising to achieve
super-high density memory and high
sensitive detection technology.
 Cell Computing

Silicon transistors at 120 nm in length
will still be 60,000 times larger in area
than molecular electronic devices.
Recent research

Recent studies have shown that individual
molecules can conduct and switch electric
current and store information.

July of 1999 – HP and the University of
California
at
Los
Angeles
build
an
electronic switch consisting of a layer
of
several
million
organic
substance
molecules
of
an
called
rotaxane.
Linking a number of switches version of an AND gate is produced.
a
Recent research
June 2002 - Fuji Xerox biotechnology made
a prototype transistor of DNA from salmon
sperm.

Researchers
successfully
passed
an
electric
current
through
the
DNAtransistor.

This
demonstrates
that
behaves
in
a
similar
semiconductor.

Super smaller chip in 10 years.
the
chain
fashion
to
Recent research
Atomic force microscope image of semi-conductive DNA compound
http://www.fujixerox.co.jp/research/eng/category/inbt/m_electronics/index.html
Self assembly
Molecular self-assembly

the
autonomous
organization
of
components into patterns or structures
without human intervention (Whitesides
2002)

Current Problem: Forming electrical
interconnects between molecules
Self assembly
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Molecular electronics
Thiol
Acetylene linkage
Benzene ring
Molecular electronics

Mechanical synthesis
 Molecules aligned using a scanning tunneling
microscope (STM)
 Fabrication done molecule by molecule using
STM

Chemical synthesis
 Molecules
aligned
in
interactions
 Self assembly
 Parallel fabrication
place
by
chemical
an atomic relay
DNA wires
DNA

Well known from biology

Forms predictable structure

Controllable
self
assembly
through base pair sequences

May be selectively processed
using restriction enzymes
http://www.chemicalgraphics.com/
DNA in microelectronics

As
the
major
component
in
a
Single
Electron Tunneling (SET) Transistor

As tags to connect up nano-circuitry
including wires and nanoparticles (taking
advantage of DNA selectivity)

As
basis
for
computation)
a
Qubit
(for
quantum
DNA SET transistor
DNA
Single electron transistor
Main strand
Gate strand
Equivalent Electrical Circuit
E. Ben-Jacob , Phys. Lett. A 263, 199 (1999).
Main strand
Assumptions

Chemical bonds(in DNA) can act as
tunnel
junctions
in
the
coulomb
blockade
regime,
could
emit
electricity, given a proper coating.

Has the ability to coat a DNA strand
with metal in nanometer scale.
Operation
Schematic image with 2 grains in DNA connected by
P-bond. Dark circle->carbon atoms, white circles>oxygen atoms.
DNA pairs

P-bond
-> tunneling junction.

H-bonds
-> capacitor.

The grain itself -> inductive properties.
DNA pairs



P bond: Has 2  bonds, 1  bond.
The  electron can be shared with 2 oxygen,
resembles an electron in well, put it on the
lowest level.
When electron enters, it meet the barrier set
by energy gap.

But the gap is narrow and
electron can walk trough.
small
so
the
DNA pairs

H-bonds: Can be the capacitor.

The proton in the h-bond can screen a net charge
density on either side, by movement.

Thus the net charge could be in the side of the h-bond.

The grains: Can be the inductive properties.

Due to the hopping of additional electrons.

But can be ignored (L & Lo is small, consistent to the
usual SET)
DNA pairs

Consist of 2 strands (1 main, 1 gate)

Connect the end base of the gate strand with a
complimentary strand.

Both strands should be metal-coated, except (a)
the grain in the main strand, which connect to the
gate strand, the
connective h-bond.

2
adjacent
P-bonds,
(b)
Connect the main strand with voltage source (V)
the
DNA pairs
The end of the gate strand with another voltage source
(Vg) that acts as gate source.
DNA conductance

Double helix – a backbone and base pairs

Building
blocks
A, T, C & G

Example: 10 base pairs per turn, distance of
3.4 Angstroms between base pairs.

Arbitrary sequences possible

A challenge for nanotechnology is controlled /
are
the
base
pairs:
reproducible growth. DNA is an example with
some success. However, there are many copies in
a solution!

2D and 3D structures with DNA base pairs as a
building block have been demonstrated

Lithography? Not yet.
DNA base-pairs
DNA conductance

Conductivity in DNA has
been controversial

Electron transfer experiments (biochemistry) /
possible link to cancer

Transport experiments (physics)
DNA conductance
Metallic, No gap
Current
Current
~ 1nA
~ 10nA
Semiconducting / Insulating
Voltage (V)
Porath et. al, Nature (2000)
Voltage 20mV
Fink et. al, Science (1999)
Counter-ions

Is conduction through the base
pair or backbone? - Basepair

When DNA is dried, where are the
counter ions?

Crystalline / non crystalline?

Counter ions significantly modify
the energy levels of the base
pairs

Counter-ion
important

Resistance
species
increases
is
also
with
length
of
the
DNA
(exponential within the
of simple models)
the
sample
context
Counter-ions
DNA-based metalised nanowires
10 nm wires:
AuPd on DNA
Methods
Schematic of undercut trench
Set-up
Schematic of electrode overlaying wire
Metalised DNA-wires
Variable width cuts in membrane, made by focused ion beam. DNA
bridges the cuts.


Longest wire to date: 960 nm (~30 nm thick)
Appearance of multi-strand “Ropes”
Metalised DNA-wires
Multi-strand “rope,” 3 nm AuPd
coating,
total thickness: 3040 nm Length: 960 nm
Two wires connected by “rope”
visible on surface of membrane,
length: 550 nm on right, 670 nm
on left
Sequence specific molecular lithography
Sequence specific molecular lithography
RecA polymerised on DNA (cryo-TEM)
Sequence specific molecular lithography
patterning of DNA metallization
Sequence specific molecular lithography
Sequence specific molecular lithography
RecA nuleoprotein filament
localised on aldehydederivatized DNA
sample after silver deposition
AFM
sample after gold deposition
SEM
Sequence specific molecular lithography
optical lithography
molecular lithography
Carbon nanotubes
Carbon nanotubes
The device - which consists of
a single-walled carbon nanotube
sandwiched
between
two
gold
electrodes
operates
at
extremely
fast
microwave
frequencies.
The
result
is
an
important step in the effort to
develop
nanoelectronic
components that could be used
to replace silicon in a range
of electronic applications (S
Li et al. 2004 Nano Lett. 4
753).
http://physicsweb.org/article/news/8/4/15
Superconductivity in nanotubes

Left red data show insulating like behavior with
resistance upturns at the lowest temperatures, blue data
show superconducting behavior

Right V-I data for a strongly superconducting sample at
various temperatures.
Courtesy, A. Bollinger
Buckyball
www.osti.gov/accomplishments/ smalley.html
Cellular computing
Cellular computing
Goals

To use a cell as the smallest DNA-based
molecular computer

More specifically, to mimic some or all
of a cells mechanisms in order to
produce
a
quasi
molecular
(QMC), or a true molecular
(TMC)
computer
computer
Quasi cellular computing

Most of the input and output operations are
driven by an external force
 Input
and programming provided, QMC
provides output
 All
molecular computers are of this
type, with the exception of the cell

Goal for QMC’s: to develop QMC’s that are
more efficient, and less dependent on
outside interaction
True cellular computing

“All
computational
operations
(input,
output, state transitions) are driven by
self organizing chemical reactions” (Ji
1999)
 All processes are internally driven, no
outside help is needed
 Only known example is a cell

Goal for TMC’s: to fabricate an artificial
TMC with the properties of a living cell
Cells versus computers
Qualities of cells that are
similar
to
those
in
computers

Have
inputs,
state
transitions, and outputs
as indicated by their
programming

Have
a
language
to
communicate between cells

Have
information
and
energy
storage
mechanisms: IDS’s
http://www.rkm.com.au/CELL/
Cells versus computers
Cells
Computers
Current carried by: Chemicals
Wires
Reactions or
Enzymes
processes turned on
or off by:
Transistors
Information stored
in:
Capacitors
Biopolymers,
IDS’s
Computational
DNA
programs stored in:
Software
Cells versus computers
Cells
Computers
Programmability No- not yet
Yes
SelfYes
Reproducibility
No- not yet
Ji, Sungchul. The Cell as the Smallest DNA Based Molecular Computer. BioSystems (1999):52 123-133.