Jim Hone (Postdoctoral fellow)
Dirk Orgassa (Postdoctoral fellow)
Ali Husain (Graduate student, Scherer group)
Henry Huang (Graduate student)
Joseph DeJesus (Undergraduate)
A carbon nanotube is a single sheet of graphene rolled into a cylinder as small as 1 nm in diameter. Both single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs), with many concentric shells, have been synthesized. The electronic properties of a nanotube depend on the angle (chirality) with which it is rolled up--nanotubes can be either metals, small-gap semiconductors, or large-gap semiconductors. Semiconducting tubes can act as field-effect transistors whose performance is now approaching that of silicon devices. Metallic tubes have shown ballistic conduction on length scales of a micron or more. Nanotubes are also the stiffest known material, with a Young's modulus of ~ 1 TPa, which makes them excellent candidates for nanomechanical systems. JH has previously studied the thermal properties of nanotubes--they show a quantized phonon spectrum due to their small size, and have tremendously high thermal conductivity.
- High Young's modulus--ideal for high-frequency devices.
- High aspect ratio--gives very high mechanical responsivity.
- Study of dissipation--there's no 'surface' for scattering, so nanotubes will offer unique insight into dissipation mechanisms.
- Small mass--ideal for high-sensitivity detection
Our Goal
To fabricate doubly-clamped beam structures with individual SWNTs and MWNTs, and measure the resonant frequency and quality factor (Q) as a function of temperature using the magnetomotive technique.
.We grow SWNTs directly on our substrates using chemical vapor deposition (CVD). This process was developed by the groups of Hongjie Dai (Stanford) and Charles Lieber (Harvard). Our method involves patterning iron catalyst in small holes (the bright circles in the AFM image to the right, with a spacing of 5 microns) on the substrate, and then growing the tubes with exposure to methane at high temperature. The nanotubes can be seen in the AFM image as the thin lines growing out of the catalyst squares.
Fabrication of suspended structures
After growth and AFM characterization, we can easily pattern leads on top of the nanotubes using e-beam lithography. The tricky part of making a suspended structure is to etch away the substrate in the area between the leads. We have been evaluating a number of different methods for doing this. Shown to the right are some of our first devices: a suspended MWNT (made in collaboration with the A.T. Johnson group at U. Penn), and a suspended SWNT. More devices are on the way!
Spin transport in nanotubes
- Observed long mean free path in carbon nanotubes suggests long spin-scattering length.
- Successfully transporting spin-polarized currents through non-magnetic materials is necessary for a new generation of electronic devices that utilize the electron spin (spintronics).
- Combined with the usefulness of carbon nanotubes as scanning probes this could open up new pathways for spin-sensitive scanning probe microscopy.
Our Goals
- Fabrication of devices consisting of ferromagnetic electrodes and SWNTs or MWNTs.
- Measurement of magnetotransport properties to determine the spin-scattering length.
- Investigate the origin of the temperature dependence of the observed magnetoresistance.
from Tsukagoshi, Alphenaar, and Ago (Nature 401, 572
(1999))
Nanotube-related publications
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Paper 1 |
