Nanoscale heat transfer

"Synthetic and bio-based lubricants are the major emerging lubricant products. This study highlights and explores key technology trends of synthetic, bio-based and mineral lubricants across a wide range of applications including turbine oil, compressor oil, gear oil, hydraulic oil, heat transfer fluids and bearing oil lubricants.  Some of the major qualities that differentiate between lubricants include viscosity index, water separation characteristics, thermal and oxidation stability, low volatility and low carbon formation, and anticorrosion.
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To assess their potential for interconnect applications, the interplay between electrical and thermal transport in carbon nanofibers (CNFs) under high-current stresses is examined. Electrical properties of CNFs bridging tungsten-deposited gold electrodes are measured. Average voltage is recorded as a function of current in each current stress cycle, and the resulting average resistance is shown to decrease with increasing stressing current. This finding reveals an important effect of Joule heating on the resistance of carbon nanostructures.

Heat generation in carbon nanofibers (CNF) has raised concerns regarding reliability in these structures under high- current conditions. This work addresses the interplay between electron transport and resulting Joule heating in CNFs. The model relates current to power dissipation leading to temperature rise in the structure, thus elucidating the relationship between thermal and electrical properties in carbon nanostructures.

The transmission coefficient for vibrational waves crossing an abrupt junction between two thin elastic plates of different widths is calculated. These calculations are relevant to ballistic phonon thermal transport at low temperatures in mesoscopic systems and the Q for vibrations in mesoscopic oscillators. Complete results are derived in a simple scalar model of the elastic waves, and results for long-wavelength modes are obtained using full elasticity theory. We suggest that thin-plate elasticity theory provides a useful and tractable approximation to the three-dimensional geometry.

Based on extensive experimental information, a model is developed that takes into account heat transport through the entire carbon nanofiber interconnect test structure and breakdown location. This electrothermal transport model elucidates observed current capacity behavior, and predicts variations in contact location with the support material. The resulting heat dissipation and current capacity are completely consistent with measurement data.

Water droplets on bare silicon surfaces are studied to examine the wetting behavior as a function of the surface energy and to parameterize water-silicon interactions in order to recover the hydrophobic behavior measured by experiments. Two different wetting regimes characterized by a critical interaction strength value are observed. At a threshold value of the water-silicon interaction parameter, water molecules start penetrating into the first layer of silicon surface under thermally vibrating walls, resulting in two distinct wetting behaviors. Fixed (cold) silicon walls do not exhibit the two different wetting characteristics. Size effects are studied for nano-scale droplets and line tension influence is observed depending on the surface wettability. Decreasing the droplet size increases the contact angle values for the low wetting cases, while contact angles decrease for smaller droplets on the high wetting surfaces. Considering the line tension effects and droplet size, εSi-O for water-silicon interactions to recover the hydrophobic behavior of silicon surfaces is estimated to be 12.5% of the value predicted using the Lorentz-Berthelot mixing rule.