Abstract
A method to measure thermal diffusivity around a single heated gold nanoparticle is presented. It is based on photothermal single particle microscopy and employs the phase delay of temperature modulation due to finite thermal diffusivity. The phase delay is detected optically averaging over the focal volume of a diffraction limited beam of light. Thermal diffusivity is extracted by comparison to electromagnetic scattering calculations of the photothermal signal. Measurements in the solid (polymer) and liquid (water) are presented and compare well with literature data. The method paves the way for extended measurements of non-diffusive and heterogeneous heat transport in complex media.
Highlights
The understanding of thermal transport processes has greatly benefitted from numerous methods that measure heat transfer close to surfaces or of macroscopic samples
We demonstrate the capabilities of quantitative single particle photothermal (PT) microscopy[11,12,13] to assess thermal diffusivities locally within a medium using a far-field optical readout
We have extended photothermal microscopy to measure thermal diffusivities with gold nanoparticles of a few nanometers in radius
Summary
The understanding of thermal transport processes has greatly benefitted from numerous methods that measure heat transfer close to surfaces or of macroscopic samples. PT microscopy is a versatile method to study absorbing particles This technique enables absorption measurements of single nanoparticles and single molecules,[16] imaging[14,17] as well as correlation spectroscopy, i.e. to investigate dynamics in solution.[18,19] The PT contrast originates from optically excited objects that dissipate their thermal energy into the surrounding medium as heat. Around these nano-sources of heat a temperature profile is created that brings about a refractive index change due to thermal expansion. Afterwards the transmission signal of the detection laser as measured by a photodiode is determined
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