Carbon nanotube bearings in theory and practice
Carbon Nanotubes (CNTs) are attractive elements for
bearings in Micro-Electro-Mechanical Systems (MEMS), because their
structure comprises nested shells with no bonding and sub-nanometer
spacing between them, enabling relative motion with low friction
and wear. A few demonstrations of CNT bearings have been reported
in the literature, and atomistic simulations have been used to
probe the properties of these bearings. This thesis extends the
state of knowledge about these bearing systems, by building on
these prior works in both the experimental and simulation domains.
The prototype CNT rotor device presented in this thesis, and
accompanying fabrication process, improve on existing CNT bearing
demonstrators by establishing a vertical bearing orientation
(enabling superior rotor balance and speed, and flexibility of
placement for drive mechanisms) and a more manufacturable process
(employing CNTs grown in place by chemical vapor deposition, and
evaluating trade-offs in growth parameters). The device consists of
a silicon rotor, supported on a cantilevered CNT shaft, and
actuated by impingement of air jets on blades around its perimeter.
For the fabrication development, extensive and consistent studies
on the compatibility of CNTs with a suite of standard MEMS process
were conducted, yielding valuable information for future CNT-based
device designers on the effects of these processes on CNTs.
Additionally, manual manipulation and placement of loose CNTs into
the required vertical alignment was demonstrated, providing an
alternate fabrication route, as well as a useful research technique
for development of CNT devices. Simulation of friction in a CNT
bearing system has been a popular topic, yet many questions remain
open. For example, the quantitative estimates of this friction
reported to date range by as much as eight orders of magnitude, and
simulation techniques employ a variety of disparate simulation
paradigms and parameters. This thesis presents a new suite of
consistently implemented but complementary and independent
simulations, which span the approaches reported to date, yet agree
quantitatively within the error margin. Furthermore, the
quantitative relationships between friction and sliding speed,
temperature, geometry, and simulation implementation parameters are
determined, and a description of the causes of friction based on
phonon analyses is offered.