Energy transport and conversion processes occur at the nanoscale due to interactions between molecules, electrons, phonons, and photons. We experimentally study these processes using laser based metrology.  Our projects benefit from collaboration with Alan McGaughey’s Lab, which makes first principles predictions of thermal transport.  Our goal is to apply our understanding to improve technologies in energy, nanoelectronics, and cryotechnology. 

Energy

Heat dissipation in solid state lighting:  LEDs will replace incandescent and flourescent lights, but their efficiency, durability, and performance is inhibited by high operating temperature.  In a DOE funded collaboration with MSE (M. Bockstaller) and Chemistry (K. Matyjaszewski), as well as researchers at Osram Sylvania, we are developing new high thermal conductivity polymers that improve heat dissipation without degrading optical performance.

Novel organic-inorganic hybrid materials for energy applications: Organic-Inorganic hybrid materials are a new class of materials assembled from organic and inorganic building blocks 1-10nm in size.  Scalable solution-based-manufacturing makes hybrids an attractive alternative to costly single crystal semiconductors for LEDs, photovoltaics, and thermoelectrics, where thermal transport is key.  In NSF funded collaborations with D. Talapin at University of Chicago and X. Roy at Columbia University, we are trying to learn how thermal energy traverses this unique hard-soft vibrational landscape?

Thermal energy storage: Phase change materials (PCMs) store thermal energy to help intermittent energy sources meet steady demands.  For example, PCMs are critical to solar thermal energy conversion.  The success of PCMs hinges upon their ability to be charged (discharged) at suitably fast rates to keep pace with dynamic loads.  We are developing 3D metal meshes that can be inserted into PCMs to enhance their thermal conductivity and charge (discharge) rates.

Evaporative heat transfer:  Meniscus evaporation controls ubiquitous industrial processes including heterogeneous bubble nucleation in boiling, desalination systems, thin film coating, and lubrication.  We seek to understand evaporative heat transfer rates in the nanoscale thin film region of the meniscus where continuum behaviors cease to exist.

NanoElectronics

Plasmonic interfaces for Heat Assisted Magnetic Recording (HAMR):  The next generation of hard disk drives will use heat to switch smaller magnetic domains (~20 nm) than ever before.  Heat is focused onto the magnetic media with a near field transducer (NFT) that propogates light along a nanoscale plasmonic interface.  Parasitic dissipation in the NFT itself (rather than in the media) causes heat fluxes at the plasmonic interface that are 100 times as high as at the surface of the sun.  In an NSF funded collaboration with Seagate Technology and the Data Storage Systems Center, we are designing adhesion layers and alloys to mitigate temperature excursions due to these heat fluxes. 

Nondiffusive thermal transport in Resistive Random Access Memory (RRAM):  RRAM offers benefits to nonvolatile memory systems due to scalability, fast switching, and easy fabrication. In RRAM, electrical stimulation switches the resistance of a metal-insulator-metal memory cell. A low-resistance state is achieved during the set process, when a nanoscale conductive filament (CF), formed by dielectric breakdown in the insulator, bridges the metal contacts. During the reset process, joule heating disrupts the CF and restores the device to a high-resistance state.

  Because the CF is smaller than the mean free paths of phonons in the surrounding insulator, heat dissipation ceases to obey Fourier’s Law. Through Boltzmann Transport Equation models and thermoreflectance measurements (see image) that uniquely expose phonon properties, we seek to understand how these nondiffusive (i.e. quasi-ballistic) thermal processes impact RRAM.  Elements of this project are funding by the NSF and Army Research Office.

Cryotechnology

Thermal conductivity of cryoprotective agents (CPAs):  Cryopreservation is the preservation of biomaterials at low temperatures through the suspension of mass transport.   Cryopreservation extends the shelf life of organs from ~24 hrs to an indefinite extent, enabling better matching and utilization of organs.   Ice crystal formation during freezing can destroy cells, so organs are perfused with viscous CPAs that forms a stable glassy (i.e. vitrified) state upon freezing.  In an NIH funded collaboration led by Y. Rabin we are measuring thermal conductivity differences between crystalline and glassy CPAs that impact cryoprotocals.