Fig. 1: Importance of interfaces on thermal conductance in micro- and nanostructured systems. 
(A) Calculations using a series resistance model for a hypothetical material with a thermal conductivity of     10 W/m-K and an interfacial thermal conductance of 100 MW/m
2K.  As the layer’s thickness decreases to less than 1 micron, thermal conductivity drops due to the interfacial contribution.  (B) Experimental measurements I made showing this effect for a PMMA/silicon interface.  The low thermal conductivity of the polymer combined with the high interfacial thermal conductance pushes these effects to the nanometer scale.  Note that silicon’s ~ 2 nm native oxide has a noticeable effect on the system’s thermal conductance.  See Ref. 2 for more details.

Heat Transport at Organic / Inorganic Interfaces

         Related Publications

1. M. D. Losego, M. E. Grady, N. R. Sottos, D. G. Cahill, P. V. Braun, “Effects of Chemical Bonding on Heat Transport Across Interfaces.” Nat. Mater. 11 502 (2012). DOI

2.  M. D. Losego and D. G. Cahill, “Thermal transport: Breaking through barriers.” Nat. Mater. 12 377 (2013). DOI

3. M. D. Losego, L. Moh, K. A. Arpin, D. G. Cahill, and P. V. Braun, “Interfacial thermal conductance in spun-cast polymer films and polymer brushes.” Appl. Phys. Lett. 97 011908 (2010). DOI

3. W-P Hsieh, M. D. Losego, P. V. Braun, S. Shenogin, P. Keblinski, and D. G. Cahill “Testing the minimum thermal conductivity model using high pressure.” Phys. Rev. B. 83 174205 (2011). DOI

Controlling heat flow in devices containing micro- and nano-scale features is important for cooling of microelectronics and energy harvesting in thermoelectrics.  As feature sizes shrink, a material’s bulk thermal conductivity (λ) becomes less important to regulating heat flow.  Interfaces within the material begin to act as the dominate thermal barriers.  Subsequently, the system’s thermal conductance is defined by the interfacial thermal conductance (G), see Fig. 1.  While simple theories exist for predicting heat flow at interfaces, they often fail to capture the complexities of real interfacial structures and do not provide adequate predictions for G.  Here, I have developed experimental methods to study interfacial structural features affecting heat flow.  Novel Au/SAM/SiO2  structures with varying interfacial bonding chemistry are fabricated using a transfer-printing route to maintain SAM integrity.  Using ultrafast pump-probe methods we can measure both heat flow and relevant structural parameters like interfacial bonding stiffness (see Fig. 2).  Using these methods we have systematically varied interfacial chemistry and have correlated interface stiffness to interfacial thermal conductance using independent quantitative measurements.  Ongoing work is investigating how these differences in bonding chemistry alter the vibrational modes contributing to heat flow across the interface to help explain the changes in interfacial thermal conductance.

Fig. 2: Effects of interfacial chemistry on heat transport across Au/SAM/SiO2 Interfaces

(A) Depiction of the transfer-printing process used to “softly” deposited Au films without damaging the SAM structure.  (1) Weakly bonded Au on SiO2 is (2) lifted from its substrate using a PDMS stamp and then (3) placed on a previously SAM functionalized receiver substrate to (4) form the final Au/SAM/SiO2 structure. This kinectically controlled process allows Au deposition on a range of surfaces irrespective of their adhesion strength.  (B) Time-domain thermoreflectance (TDTR) measurements showing the temperature decay after initial laser heating pulse demonstrating more rapid cooling for interfaces having the stronger Au/thiol bonding chemistry (blue data) than the Au/methyl van der Waals attraction.  Inset shows pico-second acoustic measurements verifying that Au/thiol interfaces also have a larger interfacial stiffness.        (C) Ability to tune interfacial thermal conductance (G) by varying the Au/thiol covalent bonding density.  See Ref. 1 for more details.


School of Materials Science & Engineering

Last Updated: June 20, 2014

© 2012 M. D. Losego