ICMCTF 2012! - CD-Lab Application Oriented Coating Development

2:30pm TS1-1-3 Surface engineering for improved thermal transport
at metal/carbon interfaces, S.V. Shenogin, UES/Air Force Research
Laboratory, Materials and Manufacturing Directorate, Thermal Sciences
and Materials Branch, US, J.J. Gengler, Spectral Energies, LLC/Air Force
Research Laboratory, Thermal Sciences and Materials Branch, US, J.J. Hu,
J.E. Bultman, UDRI/Air Force Research Laboratory, Thermal Sciences and
Materials Branch, US, A.N. Reed, A. Voevodin, A.K. Roy, C. Muratore
(chris.muratore@wpafb.af.mil), Air Force Research Laboratory, Materials
and Manufacturing Directorate, Thermal Sciences and Materials Branch,
US
Carbon nanotubes are appealing for diverse thermal management
applications due to their high thermal conductivity (as high as 3,000 W m-1
K-1) coupled with interesting mechanical properties (super-strong, but also
exhibiting foam-like deformation in CNT arrays). Unfortunately, CNT
surfaces are generally non-reactive and demonstrate weak bonding to other
materials, limiting thermal interfacial conduction. To better understand the
nature of interfacial resistance in carbon nanotubes, modeling and
experimental studies investigating engineered interfaces on highly oriented
pyrolytic graphite (HOPG) substrates were conducted. This substrate was
selected as a practical 2-dimensioinal analog for nanotube sidewalls to
facilitate modeling and experimentation, however there are differences
between HOPG and CNTs which are addressed in simulations to account
for differences in metal-carbon interfaces. Measurements of thermal
conductance at these interfaces were made by analysis of the two-color time
domain thermoreflectance (TDTR) data from the samples. The TDTR
analysis of the different metals on HOPG was made possible by having an
optical parametric oscillator on the probe beam which allows for tuning the
probe beam wavelength to match absorption bands for each metal studied.
Metal films were selected to identify effects of atomic mass, chemical
interactions (i.e., interfacial carbide formation) and electron configuration.
Measurements of chemically “inert” metals at the carbon interface,
including Al, Cu and Au demonstrated a strong dependence on Debye
temperature, with conductance values differing by a factor of 3. For metals
known to exhibit in situ formation of an interfacial carbide layer when in
contact with a carbon substrate, such as titanium and boron, conductance
values were roughly a factor of 4 higher than for inert metals. The effects of
thermal formation of interfacial carbide layers with varied areal densities on
HOPG surfaces on thermal conductance were also examined, in addition to
metal interlayers specifically selected for acoustic matching to other
materials, as in a composite structure. This work is supported by AFOSR
Low Density Materials Program, Task #2306CR7P.
2:50pm TS1-1-4 Heat flow across heterojunctions: Toward useful
nanoscale thermal interface materials, T.S. Fisher
(tsfisher@purdue.edu), S.L. Hodson, A. Kumar, Purdue University, US, A.
Voevodin, Air Force Research Laboratory, US INVITED
Improved understanding of thermal energy transport at nanometer scales
has enabled a broad range of technological advances in recent years. Today,
new materials can be designed at the atomic level and are projected to
improve the efficiency of information processing, heat transfer, and energy
conversion, among other applications relevant to aerospace vehicles and
systems. For the transfer of energy by phonons, approaches based on
atomistic Green’s functions have been recently developed and offer the
possibility of including atomic-scale detail at material interfaces, while
mesoscopic scales can be modeled with the particle-based Boltzmann
transport equation. This review will summarize a framework for the
inclusion of such high-fidelity atomistic modeling within multi-scale
modeling tools that are needed to understand complex interfacial transport
processes and scaling principles in thermal interface materials enhanced
with carbon nanotubes (CNTs). Experimental validation and refinement on
model components is essential to this work, and includes highly localized
techniques such as transient thermoreflectance techniqes, as well as
traditional 1D reference bar approaches to assess overall performance. As
an example of recent work, we briefly describe critical results related to
contact resistance measurements with CNT arrays and other graphene-based
structures. The talk will conclude with enumeration of important questions
related to heterojunction bonding and materials processing for scaled-up
manufacturing.
3:30pm TS1-1-6 Factorial increases in interfacial thermal conductance
using a monolayer, P. O'Brien (obriep3@rpi.edu), S.V. Shenogin, J. Liu,
M. Yamaguchi, P. Keblinski, G. Ramanath, Rensselaer Polytechnic
Institute, US
Manipulating interfacial thermal transport is a compelling need for a
number of technologies including nanoelectronics and biomedical devices,
solid-state lighting, energy generation, nanocomposites, and device
packaging. Here, we demonstrate that introducing a strongly-bonding
organic nanomolecular monolayer (NML) at a metal-dielectric interface
leads to a factor of four increase in the interfacial thermal conductance to
values as high as 450 MW/m 2 -K. Molecular dynamics simulation and a
vibrational analysis of NML-tailored interfaces verify that this remarkable
interfacial conductance enhancement is due to strong NML-silica and
NML-metal bonding. The strong overlap of broadband low-frequency
vibrational states at the interface further facilitates efficient heat transfer
through the molecules comprising the NML. These results provide a
rational means of increasing heterointerfacial thermal conductance through
molecular functionalization with adhesion-enhancing functional groups for
a wide variety of material systems and applications.
3:50pm TS1-1-7 Ruthenium organometallic complexes with photoswitchable
wettability for boiling heat transfer applications, N. Hunter
(chad.hunter@wpafb.af.mil), Air Force Research Laboratory, Materials and
Manufacturing Directorate, Thermal Sciences and Materials Branch, US, B.
Turner, Universal Technology Corporation, US, R. Glavin, Air Force
Research Laboratory, Materials and Manufacturing Directorate, Thermal
Sciences and Materials Branch, US, M. Jespersen, University of Dayton
Research Institute, US, M. Check, S. Putnam, Universal Technology
Corporation, US, A. Voevodin, Air Force Research Laboratory, Materials
and Manufacturing Directorate, Thermal Sciences and Materials Branch,
US
Liquid to vapor phase change technology utilizing latent heat of
vaporization, which can have heat transfer rates orders of magnitude higher
than single phase liquid cooling, is necessary for advanced aircraft due to
the onboard heat generated by high power (electrical and chemical)
components. The wettability of engineered surfaces used in these cooling
systems, in addition to other parameters such as surface roughness, is
strongly correlated to the performance of the heat exchanger systems that
use these materials. In addition to optimizing performance using passive
means (e.g., surface texturing), it would also be advantageous to control
heat transfer rates using applied stimuli (e.g., light or sound waves), which
could result in weight savings and/or energy optimization. Oxide
photocatalysts have been investigated to influence boiling performance on
surfaces 1 , but time scales for switching between wettability states are on the
order of tens of minutes to hours, much longer than for practical use to
control boiling processes. In previous work, synthesis of
[Ru(bpy)2(pox)]Cl2, an organometallic complex which undergoes reversible
photo-isomerization that changes the inherent water affinity of the
molecule, was achieved 2 . In the current research, new ruthenium-centered
organometallic complexes with functionalized bipyridine (bpy) ligands are
synthesized. The functionalization allows the Ru complexes to be
covalently tethered to metallic substrates. Surface chemistry is investigated
with XPS, indicating a character of the bonding linkage, which is then
correlated with contact angle measurements of the surface energy
modification with and without UV-VIS light irradiation. Water boiling heat
transfer studies during UV-VIS light irradiation are conducted on these
samples and correlated with the reversible switching of surface wetting.
1
Takata, et al., International Journal of Chemistry Research, 2003.
2
D.B. Turner, et al., Inorganic Chemistry, in preparation.
4:10pm TS1-1-8 From hard coatings to thermoelectrics: effects of
nanostructure on fundamental physical properties of transition metal
nitride, oxide, and oxynitride thin film alloys, B.M. Howe
(brandonhowe@gmail.com), Air Force Research Laboratory, US
Recent advances in aerospace and defense technologies have lead to an
increasing need to develop novel materials with exotic physical properties
for use in a variety of applications involving extreme, high-temperature,
high mechanical stress, and oxidizing environments. Transition metal
nitrides (TMN), oxides, and oxynitrides are well known to have remarkable
range of unique physical properties including high hardness and mechanical
strength, high melting temperatures (>>2000 °C), and tunable opticalelectronic
properties. One method to further enhance the physical properties
of many binary transition metal nitrides is to alloy them with a second
thermodynamically immiscible nitride to form metastable compounds with
enhanced physical properties. Many of these properties are accompanied by
the formation of nanoscale compositional modulations during film growth
as well as post annealing experiments, however, very little has been
reported on the ability to control this nanostructure, and as a result, the
effects of these nanostructures on fundamental physical properties is
relatively unknown.
Nanostructuring methods using these kinetically-limited growth techniques
involving high-flux low-energy ion bombardment during film growth, lead
to a unique independent control of both electric and thermal transport. The
right materials system, combined with said growth techniques, would allow
for the realization of hard, chemically inert, environmentally-friendly, and
refractory thermal-to-electrical energy conversion thin films materials to
tackle a variety of demanding defense applications.
I have used Hf1-xAlxN as a model system to study the nanostructures of
interest. I begin by reporting on the effects of nanostructure on the optical,
electronic, thermal transport and elastic constant properties of Hf1-xAlxN
69 Wednesday Afternoon, April 25, 2012