1. Carbon Nanotube Synthesis:
Characterization for use as Thermal Interface Materials
De Andre James Cherry, Timothy Jay Longson*, Ali Kashani°
Morehouse College, *UC Santa Cruz, °NASA Ames University Affiliated Research Center
Physics Department, Morehouse College & NASA MUST Consortium , Atlanta, GA, 30314.
METHODOLOGY & MATERIALS
ANALYSIS & RESULTS
CONCLUSION
RESEARCH OBJECTIVE
BACKGROUND
• Design and assemble a chamber for
growth of Carbon Nano-tubes (CNT s)
used as Thermal Interface Materials
(TIM s).
• Establish optimal environment for growth
& deposition of CNT s while retaining high
thermal conductivity.
• Overcome the difficulties associated with
lost of thermal conductivity in CNT s when
used in high density orientations i.e. CNT
forest.
The Ultimate goal of the research is to
h a r n e s s t h e r e m a r k a b l e t h e r m a l
conductive properties of discrete Carbon
Nano-tubes on a macro scale to be used to
control heat transfer and reduction.
D.) Finally, after the CNT samples
have been grown, their Thermal
Conductivity is tested using a
modified Thermal Conductivity
Meter with ASTM-D5470 Standards.
Modifications allow for both
Pressure and Temperature controls
to be altered.
Scientists have dated the existence of
Carbon Nanotubes (CNT s) in laboratories back
to approximately sixty years, 1952 to be exact;
However, it was not until the early 1990 s that a
scientist by the name of Suomo Lijima would be
recognized for the discovery of the CNT resulting
in extensive research on the subject. In these
past 20 years of research, a great deal of
information has been revealed about CNT s,
such as their advantageous property of high
t h e r m a l c o n d u c t i v i t y. E x p e r i m e n t a l
measurements have been conducted, and some
researches reported a thermal conductivity of
3000 W m-1 K-1 for a discrete multi- walled carbon
nanotube (MWNT) at room temperature.[1] This
distinct ability to transfer thermal energy
between neighboring objects is of great value to
the science of thermodynamics. A property such
as this makes CNT s ideal for the use of
materials in heat sinks of computers, thermo-
shields for spacecraft and a viable answer for
many other cooling & heating issues in various
scientific arenas.
C.) Assembled Chamber used to grow test samples
in Nano-Technology Laboratory. Vacuum capable of
pressures low as 1 torr and heater capable of
temperatures high as 800°C.
B.) Ion Beam Sputter used to deposit Iron (Catalyst)
and Aluminum (Diffusion Barrier) on to Silicon
Substrate Capable of 50nm thicknesses.
FUTURE WORK
REFERENCES
CNT Forrest viewed through Scanning Electron Microscope order of
1.3K magnification.
National Aeronautics and Space Administration
Screen shot depicting vital information during Vacuum Chamber operation i.e. Temperature, Pressure & Gas Mixtures
ì îA.) Sterilized and Prepared Silicon Wafers for use
as Substrates to deposit Carbon Nanotubes.
í
D.) Thermal Conductivity Meter ASTM-D5470
Standard with Modifications. Both pressure and
temperature settings can be manipulated.
ë
A.) Good samples are results of
good preparation. To increase the
integrity of the CNTs the Silicon
substrates are sterilized with an
Acetone wash. The substrate is
handled with protective equipment
from this point forward.
C.) The Chamber uses Argon,
Hydrogen & Ethylene in varying
mixtures called recipes to grow the
CNTs. Currently the chamber is
used at a constant Pressure &
Temperature. The most recent CNT
samples were grown at a pressure
of 450 torr and a temperature of
760°C.
B.) Before the CNTs are grown, the
silicon substrate is coated with an
Aluminum & Iron layering in an Ion
Beam Sputter. This Sputtering
process further insures enhanced
adhesion of the Carbon Nanotubes
to the silicon substrate.
Based on the experiment thus far,
researchers believe that by growing the
carbon nanotubes in various conditions
such as different Pressures & Temperatures,
in addition to manipulating the densities of
CNT forest, it will soon be possible to
establish and produce carbon nanotube
forest with thermal conductive properties
that rival those of discrete carbon
nanotubes. A scientific breakthrough of that
magnitude could result in numerous smaller
more complex and energy efficient
electronics and mechanical devices that will
greatly improve our day-to-day lifes.
Once the Chamber had been assembled and Calibrated, the system was
ramped to predetermined conditions. As displayed by the graph below, the
temperature of the chamber was raised to approximately 760°C and the
pressure inside the chamber was kept constant at 450 torr. So far only one
recipe mixture has been used to grow CNTs in the chamber; however, more
recipes will be tested in the near future.
• Develop and test new growth
recipes for use in the Chamber.
• Determine number of CNT units in
specified area using Electron
Scanning Microscope.
• Analyze samples for Thermal
Conductivity using the Thermal
Conductivity Meter.
Analyzing the results of the first CNT
growth is the next major task of the
research, so that new chamber recipes
can be created for improvement of the
thermal conductive property in the
CNTs.
[1] Hua Huang, Changhong Liu, Yang Wu, Shoushan Fan Advanced
Materials 2005, 17, 1656-1661