Time-resolved optical measurement of thermal transport by surface plasmon polaritons in thin metal stripes

Abstract

We investigate the thermal transport originating from the propagation of surface plasmon polaritons (SPPs) in a thin gold stripe. The SPPs are excited by a grating coupler on the Au stripe which was patterned onto a silicon membrane. The transmissivity changes of the Si membrane due to temperature-induced changes of the interference conditions enable measuring the temperature distribution with temporal and spatial resolution better than 1 ls and 1 lm. With this setup, we demonstrate that SPP excitation, propagation, and decay are accompanied by considerable heating and heat transport. V C 2014 AIP Publishing LLC. [http://dx.Heat management in nanoscale junctions is a fast growing field of interest in nanoscience for fundamental reasons as well as for application. [1][2][3][4][5][6][7][8][9][10][11][12][13] In many experiments, metallic nanoelectrodes act as optical antenna for local enhancement of the electrical field created by laser irradiation. 14,15 In this context, localized surface plasmons as well as running surface plasmon polaritons (SPPs) 16-19 might have a major impact for the interpretation of nano-optoelectronic experiments. 20-24 A prerequisite for assessing these nanoscale effects is the understanding of heat transport by plasmons in mesoscopic systems, where a local equilibrium between the electronic and the phononic system can safely be assumed and, thus, a local temperature is well-defined. In metallic nanoparticles, localized plasmons can lead to hot spots with very high field intensities, leading, e.g., to local photopolymerization of surrounding resist and even to local melting of the nanostructures. 25,26 In this paper, we address propagating SPPs in micron size gold stripes and show how the lateral heat flow and dissipation by SPPs in such systems can be directly measured by optical inspection. 27 Our data demonstrate that the contribution of SPPs can lead to a distinct local temperature increase, illustrating that the decay of SPPs along their propagation path has to be taken into account in the heat management of plasmonic devices.Our experimental set-up is shown in Fig. 1(a). It relies on the temperature dependence of the optical transmissivity of a thin, free-standing Si membrane, as described previously. 27 The membrane (thickness 340 nm, area 700 lm  700 lm) is homogeneously illuminated by light with a wavelength of 488 nm (using a high power white light light emitting diode (LED) and an optical bandpass filter (61 nm)), and the transmissivity is measured with a lateral resolution of about 1 lm by an optical microscope combined with a sensitive CCD camera. In our measurement, a local temperature increase of 1 K led to a change of transmissivity of the membrane of 0.4%, which was readily observable with our set-up. By pulsing the LED, snapshots of the twodimensional temperature distribution across the membrane could be taken, with a time resolution in the range of 100 ns (depending on the duration of the LED probe pulse).For the investigation of the heat release related to SPP propaga...

Fast quantitative optical detection of heat dissipation by surface plasmon polaritons

“…This is only a small effect, however, as was shown for unpatterned films in ref. 38, and is confirmed in the ESI in Fig. S4.…”

“…The samples under study feature an Au stripe of 100 nm thickness and 4 μm width evaporated on a free-standing Si membrane of thickness 340 nm and 700 μm × 700 μm area supported by a massive Si wafer with a thickness of ∼500 μm. 38 Finally, grooves were carved in the metal by FIB in order to form line gratings for the excitation of surface plasmons. The gratings are chosen to compensate the momentum mismatch between the SPPs and the exciting photons with wavelength λ = 785 nm (ref.…”

“…1(b) and has been described previously. 38,39 It consists mainly of an optical microscope which allows one to observe the optical transmissivity of the Si membrane samples with a high spatial resolution, a laser focused to 3 μm diameter for the excitation of SPPs, and a pulsed light emitting diode which provides the illumination of the Si membrane. Since the transmissivity exhibits a pronounced temperature dependence, 39 the lateral temperature distribution in the membrane can be inferred from the transmitted light, recorded by a digital camera.…”

“…In a previous publication we have shown that it is possible to detect the presence of propagating SPPs by means of their decay into phonons, measuring the resulting temperature increase along the propagation path. 38 In this article we show that the lateral heat flow and the heat dissipation by SPPs in a micron size gold stripe can also be quantitatively determined from an optical inspection of the temperature distribution around the stripe combined with computer simulations. 39 A thin silicon membrane, used as a substrate for the gold stripe, serves as a medium for obtaining temperature maps with sub-μm spatial and sub-μs temporal resolution.…”

“…The details of the measurement procedure have been published in ref. 38 and are given in the Experimental section and the ESI. †…”