Thermal Transport Properties of Nanostructures Immobilized Substrates
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1172-T01-03
Thermal Transport Properties of Nanostructures Immobilized on Substrates Hugh H. Richardson1, Alyssa C. Thomas1, Michael T. Carlson1 and Alexander O. Govorov2 1 Department of Chemistry and Biochemistry, Ohio University, Athens, Ohio 45701. 2 Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701. ABSTRACT We characterize a temperature sensor made from Erbium ions embedded in an amorphous AlGaN matrix that is accessed remotely by measuring the relative intensities from photoluminescence peaks of Er3+. We use this sensor to measure the nanoscale temperature around an optically excited single gold nanoparticle that has been immobilized on the AlGaN substrate. The maximum temperature increase measured experimentally is 8.3 K. The temperature measurement is diffraction limited by our microscope to 490 nm. This temperature corresponds theoretically to a maximum local temperature increase of 22 K. A straight-forward analysis using energy balance gives the thermal conductivity of the amorphous AlGaN substrate as 4.5 W/m-K. INTRODUCTION Understanding heat transfer at the nanoscale is essential to predict and control the thermal energy balance in nanodevices and other nanostructures. As device dimensions continue to be reduced and number densities increase, heat dissipation becomes an increasingly serious problem. We have recently shown that a single isolated metal nanoparticle can generate sufficient heat upon irradiation to induce readily observable phase changes in ice and water1-5. The amount of phase change can serve as the basis for sensitive nanocalorimetry experiment in which the temperature profile around a nanoparticle heat source can be measured as a function of optical energy input. We extend our nanocalorimetry experiments by constructing a sensitive nanoscale thermometer made from the photoluminescence properties of Erbium doped in AlGaN. This optical thermal sensor can be used to map the temperature, on a nanometer scale, from optically-excited nanostructures. In this paper we purposefully induce heating of a single gold nanoparticle by optical excitation and indirectly measure the resulting heating effects of the gold nanoparticle using the Erbium ions within the AlGaN matrix. We characterize the AlGaN:Er temperature sensor and present a thermal image of a single gold nanoparticle excited with 532 nm light with a flux of 23 x 104 W/cm2. EXPERIMENTAL Figure 1 shows our experimental diagram for collecting photoluminescence and Raman scattering from a single gold nanoparticle. The laser is defocused to the surface but the collection optic is focused on the gold nanoparticle (40 nm diameter) that has been immobilized to the surface2. The laser beam profile on the surface is adjusted to give a Gaussian profile that has a FWHM of 2000 nm. The collection optics is a 50X dark field objective that gives a diffraction limited spatial resolution of ~ 490 nm. The
AlGaN:Er/Si(001) substrate has been described in a previous publication6 as well as the peak intensity temperature dependence fo
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