AVS 58th Annual International Symposium and Exhibition
    Advanced Surface Engineering Division Wednesday Sessions
       Session SE+SS-WeM

Paper SE+SS-WeM9
Thermal Characterization of Metal/Carbon Interfaces: Comparison of Metallized Nanotubes and Graphite

Wednesday, November 2, 2011, 10:40 am, Room 104

Session: Surface Engineering for Thermal Management
Presenter: Adam Waite, Air Force Research Laboratory
Authors: C. Muratore, Air Force Research Laboratory
S. Shenogin, Air Force Research Laboratory
A. Waite, Air Force Research Laboratory
A. Reed, Air Force Research Laboratory
J. Gengler, Air Force Research Laboratory
T. Smith, Air Force Research Laboratory
J. Hu, Air Force Research Laboratory
J. Bultman, Air Force Research Laboratory
A.A. Voevodin, Air Force Research Laboratory
Correspondent: Click to Email
Most applications of carbon nanotubes require contact with more ordinary materials, such as metals or polymers. Unfortunately, the extraordinary thermo-electro-mechanical properties of nanotubes are often negated at the interface between the nanotubes and whatever they touch, resulting in a major shortfall between the measured and predicted performance of nanotube-based materials. One of the most troubling discrepancies in projected versus measured properties is found in thermal conductivity measurements of nanotube-containing composite materials. For example, a continuous network of thermally conductive nanotubes (or about 1 percent, by volume) within an organic matrix (k = 0.3 W m-1 K-1) should yield a 30-fold increase in thermal conductivity over the pure matrix phase alone, based on simple effective medium theory. Despite this potential increase, experimental results typically show an increase of only a factor of 2 at best in composites with nanotube additives. To better understand the nature of interfacial resistance in carbon nanotubes, modeling and experimental studies investigating engineered interfaces on highly oriented pyrolytic graphite (HOPG) samples were conducted. This substrate was selected as a practical 2-dimensioinal analog for nanotube sidewalls to facilitate modeling and experimentation. Molecular dynamics simulations of heat transfer through metal carbon interfaces were conducted, and 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 wavelength to match absorption bands for each metal studied. Comparison of simulation and experimental results between graphite and nanotubes is highlighted. Metal films were selected to identify effects of atomic mass, chemical interactions and mechanical properties. For example, metals known to exhibit in situ formation of an interfacial carbide layer when in contact with a carbon source and heated, such as titanium and boron, were investigated, and the effect of this carbide layer formation on interfacial conductance was examined. Graded and sharp interfaces were also considered with computational and experimental efforts.