Transcript Imaging & Actuation of Nanocar Molecules by Scanning

Imaging & Actuation of Nanocar Molecules by Scanning Tunneling Microscopy
(NIRT – ECCS #0708765)
A. J. Osgood,1 J. Zhang,1 T. Sasaki,2 J. Guerrero,2 J. M. Tour,2 and K. F. Kelly1
1Department
of Electrical & Computer Engineering,
Molecular
Manipulation
2Department
of Chemistry, Rice University
Molecular
Tinkertoys
Nanoscale Rolling by Fullerene Rotation
Transport of goods and materials between points
is at the heart of all engineering and construction
in real-world systems. With existing biological
systems adept at the transport and manipulation
of molecular-sized entities, as we delve into the
arena of the nano-sized world it beckons that we
learn to manipulate and transport nanometerscale materials in a similar manner.
Piezo actuators
Z
DC
Bias
X
Y
C10H21O
H
C10H21O
Computer &
Electronics
Tunnel
Current
A
The closed cage structure of C60 molecules allows them to roll in a
wheel-like fashion when attached by freely rotating alkyne bonds to a
central connecting structure. The Nanocar – four fullerenes connected
by parallel Oligo (phenylene ethynylene) or OPE “axles” – has
demonstrated directional preference due to this rolling. Both direct tipmanipulation, as seen above, and substrate annealing up to 240 ºC, seen
on the left, have shown that the Nanocar moves much more easily in a
direction perpendicular to the axles.
H
H
Pulling
Sliding
OC10H21
OC10H21
H
+1.0 V
0.10 nA
C10H21O
OC10H21
OC10H21
OC10H21
H
9.4nm
H
C
D
E
Pushing
OC10H21
The chemistry behind these various molecules
has created a kind of molecular tinkertoy set,
with varying arrangements of Oligo (Phenylene
Ethynylene) constituents. Molecules of various
sizes and configurations have been synthesized
and characterized, exhibiting a unique collection
of surface properties and behaviors including
significant flexibility, atomic step crossing, and
rolling surface mobility.
B
With its ability to image and manipulate individual
atoms and molecules, scanning tunneling microscopy
(STM) is the ideal tool to begin our study of
specifically designed and synthesized nanomachines.
Manipulation by STM can be achieved by variation in
electric field with the changing bias voltage, electron
injection by increasing the tunneling current, and/or
van der Waals interactions by adjusting the tip-sample
separation. Depending on the molecular system,
these will result in pushing, pulling, or sliding of
molecules.
Tip Motion
C10H21O
C10H21O
Amp
Constant current imaging
C10H21O
Apparent fullerene size is partly influenced by whether the molecules are
rotating or stationary. Rotating fullerenes appear larger, which was used
to test whether temperature directly effects fullerene rotation on
Nanocars. Automated analysis of Nanocar fullerenes shows through
height histograms that higher temperatures produce higher fullerenes,
indicating that more are rotating at higher temperatures.
Three-fullerene
“pinwheels,” designed
for constrained motion,
only pivoted in place
under
the
same
conditions that induced
motion in the Nanocar.
Carborane Wheeled Molecules
Unlike the other carborane
wheeled and fullerene wheeled
nanocars, the internal OPE
structures of the Carborane
Trimer are visible.
The smaller carborane wheels of this six-wheeled
nanocar are still plainly visible via STM on a Au(111)
surface, though the inner structure proves difficult
to resolve.
Nano Traffic Jam: Due to the contamination during
the deposition process, the carborane wheeled
nanocars and the fullerene wheeled nanocars
appeared on the same STM image, providing a
direct juxtaposition of their sizes.
6.5 nm
Azo-fullerene
R
R
1
2
1
2
2.6nm
3.8nm
The
internal
azobenzene
moiety can be switched from
R
R
“trans” to “cis” by UV (~350
1
1
2
nm) and switched back by
Blue
(~440
nm)
light
2
irradiation. Its configuration
2.8nm
2.8nm
also can be switched on
metal surface by STM tip An azo-fullerene dimer has been created by adding two fullerene
wheels and phenyl groups to azobenzene. Tip-induced motion has been
voltage pulse.
performed successfully.
Azo-Nanocar
1.60
A C10 alkanethiol self assembled monolayer
(SAM) was chosen as an insulating surface to
reduce the gold’s quenching effects which
inhibit
photon-induced
switching.
After
depositing the molecules on the SAM on
Au(111), the Azo-fullerene dimers were
switched by illumination from a 400nm LED.
2.65
4.60
3.07
1.62
1.65
2.00
3.1
8