CAREER:Thermal Energy Transport in Organic-Inorganic Hybrid Materials

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PI: Jonathan A. Malen, Carnegie Mellon UniversityProposal Number: CBET-1149374The objective of this CAREER proposal is to study thermal transport in organic-inorganic hybrid materials. Organic-Inorganic Hybrid Materials are attractive alternatives to single crystal semiconductors for electronics, photonics, and energy conversion because they can be manufactured with scalable solution-based processes. For these applications the organic-inorganic interface has been leveraged to control electronic transport, but thermal properties remain uncultivated. It is hypothesized that collective properties, emergent at the organic-inorganic interface, will enable unprecedented control of the thermal phonon spectrum in hybrid materials. The intellectual merit of the proposal centers around the experimental measurement of thermal transport in two novel hybrid materials: self assembled monolayers (SAMs) and nanocrystal superlattices (NCSLs). SAMs are 2-D molecular crystals that form on inorganic surfaces, and NCSLs are 3-D arrays of inorganic spheres spaced by organic molecules. Coupling and alignment of dissimilar vibrational states in the organic and inorganic components can be controlled by chemistry to yield diverse thermal transport properties. These effects will be experimentally interrogated through (i) the development of a new continuous-wave laser method to probe an unparalleled range of phonon mean free paths in solids, (ii) measurements of thermal conductivity and phonon mean free path distributions in NCSLs, and (iii) systematic measurements of SAM interface thermal conductance.The ability to manipulate the phonon spectrum will broadly impact a wide range of applications in energy and biology. Due to short phonon wavelengths (10 nm), hybrid based phonon-optics would achieve much higher resolution than visible light having much longer wavelengths. Such non-destructive imaging can be extremely useful in assays of biological, organic, and inorganic samples. Further, solution chemistry based manufacturing and tunable electro-optic properties make hybrids ideal for energy conversion technologies that demand wide deployment, including thermoelectrics, photovoltaics, and LEDs. Engineering hybrid devices requires knowledge of their hitherto unknown thermal properties, whereas phonon control can yield unique performance upgrades. Bandpass filtering of phonons by SAMs can increase the efficiency of optoelectronics, while decoupled thermal and electronic transport properties make NCSLs ideal for thermoelectric waste heat conversion. An integrated educational plan that aspires to demystify the phonon is highlighted by the "Phonon-Simulator", a model spring-mass system that simulates vibrations in matter. This educational kit will be paired with online software and deployed throughout the Pittsburgh Public Schools (PPS) to introduce the origins of heat transfer through an interactive educational program. The local focus will be underrepresented pre-college students from PPS as well as students at Carnegie Mellon. Broader dissemination will be achieved by workshops at the Intel International Science & Engineering Fair and the Siemens Competition, aimed at jointly recruiting scholars into engineering.