Nanoparticles are widely used in composite materials and nanoscale devices. Thus, characterization of the thermophysical properties of a single nanoparticle is of great importance for both nanotechnology and nanoscience applications. However, conventional measurement methods cannot be used to determine the thermophysical properties of a single nanoparticle. Due to their small size and small mass, the specific heat of a nanoparticle is extremely tiny. Thus, the temperature variations with time for a nanoparticle are very hard to measure by a contact sensor. Non-contact measurement methods are high speed measurements to resolve the temperature rise of the nanoparticle. However, there are no effective heat flux meters for non-contact measurements. Thus, the thermal parameters cannot be easily separated by non-contact measurement methods. This study characterizes the thermophysical properties of a single nanoparticle by combining non-contact measurement data with contact measurements to decouple the various parameters. The measurements combine a contact Joule heating method with a non-contact laser flash tip-enhanced Raman spectroscopy method to characterize the specific heat of a single nanoparticle. A contact probe is first used to heat the single nanoparticle with the heating power measured with and without contact with the nanoparticle to determine the effective heat transfer coefficient to the nanoparticle. A series of square laser pulses are used to heat the sample with the temperatures then measured by their Raman band shifts, which gives the temperature changes for a lumped parameter model. The tip-enhanced Raman spectroscopy method gives high spatial resolution. The laser light absorptivity of the nanoparticle is then eliminated by comparing the temperature rises measured using different laser pulse widths. The specific heat of the nanoparticle is then extracted by fitting the normalized temperature rise curves. The lumped model is shown to be accurate when Bi<0.11 and 1/Fo>1.2 for which the maximum temperature difference within the nanoparticle is less than 10%. The nanoparticle can then be regarded as a zero-dimensional model and the lumped model will give reasonable results. Simulations with typical nanoparticle properties show that the temperature measurements need to be faster with lower specific heats. For a 100 nm diameter nanoparticle with a specific heat of about 1×10 2 J/(kg K), the temperature rise will approach steady state within about 20 ns, so the smallest pulse width should be about 1 ns. However, for a specific heat on the order of 10 3 J/(kg K), the smallest pulse width can be 10-50 ns. The influence of ignoring the temperature rise of the substrate is also discussed. Simulation of typical conditions shows that the nanoparticle temperature rise is about 10 4 times the highest temperature rise of the substrate. Therefore, the temperature rise in the substrate can be neglected. Other possible difficulties of this method are also analyzed in this paper.
|Translated title of the contribution||Joule heating and laser flash tip-enhanced Raman spectroscopy method for characterizing the specific heat of a single nanoparticle|
|Original language||Chinese (Traditional)|
|Number of pages||8|
|Journal||Kexue Tongbao/Chinese Science Bulletin|
|Publication status||Published - Sept 25 2018|
All Science Journal Classification (ASJC) codes