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Vibrational and electronic heating in nanoscale junctions


Understanding and controlling the flow of heat is a major challenge in nanoelectronics. When a junction is driven out of equilibrium by light or the flow of electric charge, the vibrational and electronic degrees of freedom are, in general, no longer described by a single temperature1,2,3,4,5,6. Moreover, characterizing the steady-state vibrational and electronic distributions in situ is extremely challenging. Here, we show that surface-enhanced Raman emission may be used to determine the effective temperatures for both the vibrational modes and the electrons in the current in a biased metallic nanoscale junction decorated with molecules7. Molecular vibrations show mode-specific pumping by both optical excitation8 and d.c. current9, with effective temperatures exceeding several hundred kelvin. Anti-Stokes electronic Raman emission10,11 indicates that the effective electronic temperature at bias voltages of a few hundred millivolts can reach values up to three times the values measured when there is no current. The precise effective temperatures are model-dependent, but the trends as a function of bias conditions are robust, and allow direct comparisons with theories of nanoscale heating.

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Figure 1: Measurement overview.
Figure 2: Optically driven vibrational pumping.
Figure 3: Electrically driven vibrational pumping.
Figure 4: Electronic heating under bias.


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D.N. and D.R.W. acknowledge support by the Robert A. Welch Foundation (grant C-1636) and the Lockheed Martin Advanced Nanotechnology Center of Excellence at Rice (LANCER). D.N. and D.R.W. acknowledge valuable conversations with M. Di Ventra, M.A. Ratner and A. Nitzan.

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D.R.W. fabricated the devices, performed all measurements, and analysed the data. D.N. supervised and provided continuous guidance for the experiments and the analysis. D.A.C. synthesized the OPV3 molecules under the supervision of J.M.T. The bulk of the paper was written by D.R.W. and D.N. All authors discussed the results and contributed to manuscript revision.

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Correspondence to Douglas Natelson.

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The authors declare no competing financial interests.

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Ward, D., Corley, D., Tour, J. et al. Vibrational and electronic heating in nanoscale junctions. Nature Nanotech 6, 33–38 (2011).

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