Towards Single Molecule Electronics

1
Towards Single Molecule Electronics
Can a single molecule behave like a
diode,
transistor (switch), memory ? If thats
possible, how long will the molecule last
? First, lets look at many molecules acting in
parallel.
Nitzan and Ratner, Science 300, 1384 (2003)
Heath and Ratner, Physics Today, May 2003, p. 43
2
HP Molecular Memory
40 nm line width, 40 Gbit/inch2
3
Molecular Memory
DRAM
MRAM (Magnetic Random Access Memory)
4
HP Molecular Memory
Rotaxane molecules switch between high and low
resis- tance by receiving a voltage pulse.
The blue ring can shuttle back and forth along
the axis of the rotaxane molecule, between
the green and red groups.
5
HP Molecular Memory
Change the resistance between low and high by
voltage pulses.
Is the resistance change really due to the
rotaxane ring shuttling back and forth? Other
molecules exhibit the same kind of switching.
One possible model is the creation and
dissolution of metal filaments which create a
short between the top and bottom electrodes.
(Some-thing like that happens in batteries).
Collier et al., Science 289, 1172 (2000).
6
Other Molecular Switches
Large On-Off Ratios
Chen et al., Science 286, 1550 (1999)
7
Robert F. Service, Science 302, 556 (2003).
8
Synthesis of a Rotaxane Molecule
Amabilino and Stoddart, Chemical Reviews 95, 2725
(1995).
9
Some Fancy Molecules
Rotaxane
Catenane Pretzelane
Handcuffcatenane
10
Data Storage via the Oxidation State of a
Molecule
Electrochemistry
11
Self-Organizing Memory Data Processor
People have been thinking about how to combine
memory with logic ( a microprocessor) in a
molecular device. Self-assembly is the preferred
method. It generates errors, though. They
need to be absorbed by a fault-tolerant
architecture (e.g. in the HP Teramac)
Heath et al., Science 280, 1716 (1998)
12
Local Hotspots Appear after Switching
The latest from HP on how molecules switch.
Miao et al., Phys. Rev. Lett. 101, 016802 (2008)
13
Conductivity of DNA
Tunneling at short distances (independent of
temperature) Hopping at large distances
(thermally activated)
Berlin et al., Chem. Phys. 275, 61 (2002)
14
Using a Single Molecule
15
Using a Single Molecule
Coulomb Blockade Magnetic (Kondo)
Resonance at the Fermi level (zero voltage)

Park et al., Nature 417, 722 (2002)
16
Using a Few Molecules
Observe tunneling through 1, 2, 3, 4, 5
alkanethiol molecules
Cui et al., Science 294, 571 (2001)
17
A Molecular Transistor
(a) Structures of the long and short linked
cobalt coordinated terpyridine thiols used as
gate molecules. (b) A topographic AFM image of
the gold electrodes with a gap. (c) A schematic
representation of the assembled single atom
transistor.
18
Break Junctions
At the beginning of single molecule electronics,
break junctions were very popular Just crack a
thin Au wire open in a vice and adjust the width
of the crack with piezos (as in STM). Then pour a
solution of molecules over it. Alternatively, one
can burn out the thinnest spot of a thin
Au wire by running a high current density
through it (using the effect of
electromigration). These days, many try to
achieve a well-defined geometry using a STM or
AFM, with a well-defined atom at the end of the
tip and another well-defined atom at the surface
as con-tacts to a single molecule.
A schematic representation of Reed and Tours
molecular junction containing a
benzene-1,4-dithiolate SAM that bridges two
proximal gold electrodes.
19
Conductance through a C60 Molecule
Distance dependence tells whether it is tunneling
(exponential decay) or quantum conductance
through a single or multiple orbitals (G0).
Kröger et al., J. Phys. Condend. Matter 20,
223001 (2008)
20
Many Ideas for Single Molecule Devices
Heath and Ratner, Physics Today, May 2003, p. 43