Thermo-optical Responses of Nanoparticles: Melting of Ice and Nanocalorimetry Approach

Abstract

The thermo-optical properties of gold nanoparticles (NPs) embedded in an ice matrix were investigated using photoluminescence and Raman spectroscopy. An intense laser beam alone will not melt ice, but the addition of embedded Au NPs allows for melting with resonant laser light of relatively weak intensity. This is due to the strong absorption of Au NPs in the plasmon resonance regimen. We can determine the threshold melting power, P melting (T), where T is the background temperature by recording time-resolved Raman scattering signals of the system. A resultant loss of ice signal indicates melting and an absence of conversion to water implicates an irreversible loss of water molecules to the gas phase due to the location of the Au NP agglomerate at or near the ice/vapor surface. For fully embedded NP agglomerates, the ice/water phase transition can be monitored through Raman spectroscopy and the number of NPs in an agglomerate and their interactions can have a greater effect on localized heat generation. The local temperature inside and around the NP agglomerate depends strongly on its geometry and leads to a large scatter in the measured P melting as a function of the reduced temperature for different agglomerates. Immobilized Au NP agglomerates can also be characterized using single-particle spectroscopy, and results show that the plasmon emission of Au NPs scales with the number of NPs in an agglomerate.

Experimental and Theoretical Studies of Light-to-Heat Conversion and Collective Heating Effects in Metal Nanoparticle Solutions

“…Some measurements have been made to directly measure the temperature on the surface of Au NPs when optically excited10, 12, 15, 49, 50. The heating effect is especially strong for metal NPs since they have many mobile electrons and becomes strongly enhanced when the laser frequency hits the collective plasmon resonance of a NP.…”

“…they are very poor light emitters), the total amount of heat generated is expected to be related to the total optical absorption rate in a relatively simple and straightforward way. Energy balance arguments would suggest that if the optical quantum yield of NPs is very low (10 −6 )51 then there should be a near unity conversion of photon energy into heat3, 10, 15, 49, 51, 52. In contrast to this viewpoint, a recent paper suggests that the efficiency of transducing incident resonant light to heat for a suspension of 20 nm Au NPs is small (less than 5%) and can be increase to by modulating the continuous wave (CW) laser light 53.…”

Thermal Effects of Colloidal Suspensions of Au Nanoparticles

“…Understanding the thermal properties of optically stimulated nanoparticles has become of great interest as of late [1][2][3][4][5] . The study of this new class of materials known as nanoheaters includes understanding the heat-generating behavior of nanostructures under optical illumination.…”

Probing ice-nucleation processes on the molecular level using second harmonic generation spectroscopy

“…Various methods have been employed to study heterogeneous IN, e.g. infra-red spectroscopy (Richardson et al, 2007;Sadtchenko and Ewing, 2011). Following this, one promising approach to elucidate these structures on the molecular level is nonlinear optical (NLO) spectroscopy.…”