We investigate the response of multi-walled carbon nanotubes to mechanical strain applied with an Atomic Force Microscope (AFM) probe. We find that in some samples, changes in the contact resistance dominate the measured resistance change. In others, strain large enough to fracture the tube can be applied without a significant change in the contact resistance. In this case we observe that enough force is applied to break the tube without any change in resistance until the tube fails. We have also manipulated the ends of the broken tube back in contact with each other, re-establishing a finite resistance. We observe that in this broken configuration the resistance of the sample is tunable to values 15-350 kΩ greater than prior to breaking. Soon after their discovery by Iijima, carbon nanotubes 1 (CNTs) were predicted to have interesting electrical
The transfer of electrons from one material to another is usually described in terms of energy conservation, with no attention being paid to momentum conservation. Here we present results on the junction resistance between a carbon nanotube and a graphite substrate and show that details of momentum conservation also can change the contact resistance. By changing the angular alignment of the atomic lattices, we found that contact resistance varied by more than an order of magnitude in a controlled and reproducible fashion, indicating that momentum conservation, in addition to energy conservation, can dictate the junction resistance in graphene systems such as carbon nanotube junctions and devices.
We report the successful synthesis of nanoscale peapods from single-walled and double-walled nanotubes grown by chemical vapor deposition (CVD) on substrates with windows etched into free-standing silicon nitride membranes. CVD-grown nanotubes were oxidized in air, then filled with C(60) molecules from the vapor phase. Observed variation in nanotube oxidation and C(60) packing with nanotube diameter agreed with theoretical expectations. Windowed samples provide several important advantages for property measurements of peapods and other nanomaterials. Individual nanostructures can be followed through processing steps, and a single nanostructure can be inspected by high-resolution TEM and subsequently contacted with nanoscale electrodes using electron beam lithography.
In many cases in experimental science, the instrument interface
becomes a limiting factor in the efficacy of carrying out unusual
experiments or prevents the complete understanding of the acquired data.
We have developed an advanced interface for scanning probe microscopy
(SPM) that allows intuitive rendering of data sets and natural instrument
control, all in real time. The interface, called the nanoManipulator,
combines a high-performance graphics engine for real-time data rendering
with a haptic interface that places the human operator directly into the
feedback loop that controls surface manipulations. Using a hand-held
stylus, the operator moves the stylus laterally, directing the movement of
the SPM tip across the sample. The haptic interface enables the user to
“feel” the surface by forcing the stylus to move up and down
in response to the surface topography. In this way the user understands
the immediate location of the tip on the sample and can quickly and
precisely maneuver nanometer-scale objects. We have applied this interface
to studies of the mechanical properties of nanotubes and to
substrate-nanotube interactions. The mechanical properties of carbon
nanotubes have been demonstrated to be extraordinary. They have an elastic
modulus rivaling that of the stiffest material known, diamond, while
maintaining a remarkable resistance to fracture. We have used atomic-force
microscopy (AFM) to manipulate the nanotubes through a series of
configuration that reveal buckling behavior and high-strain resilience.
Nanotubes also serve as test objects for nanometer-scale contact
mechanics. We have found that nanotubes will roll under certain
conditions. This has been determined through changes in the images and
through the acquisition of lateral force during manipulation. The lateral
force data show periodic stick-slip behavior with a periodicity matching
the perimeter of the nanotube.
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