Ultrafast heating with plasmonic nanoparticles: A scaling analysis of particle, interface and medium effects

<jats:p>Metal nanoparticles strongly absorb light at their localized surface plasmon resonance (LSPR). The absorbed energy generates plasmons under femtosecond excitation, which decay and lead to ultrafast heating of the particles. Thus, these materials can be utilized as nanoheaters to increase the temperature of their local environment on picosecond to nanosecond timescales. The temperature increase of the surrounding medium, as well as their cooling timescales are governed by several factors. These include excitation conditions, the optical and thermal properties of both the metal and the medium, as well as the nature of the interface. Despite extensive studies, particularly on interfacial effects in heat transfer dynamics, a framework linking these experimental parameters to key system descriptors such as the particle temperature decay time and the temperature increase in the medium is lacking. Here, we address this issue by identifying the governing parameters controlling heat transfer rates via a scaling analysis using a continuum heat transfer model. We use transient absorption (TA) spectroscopy to probe ultrafast heating in colloidal gold nanoparticles in a liquid solution. We experimentally obtain temperature profiles of both the particles and the medium and determine the interface thermal conductance (ITC), G. The scaling analysis reveals distinct regimes limited by interface thermal conductance or thermal diffusion in the medium. We demonstrate a shift from an interfacial effects dominated heat transfer regime to a thermal diffusion dominated regime by changing particle size, surface ligands, and the surrounding medium. This way, we show that a simple scaling approach captures the tunability of the particle cooling timescales and temperature increases in the medium based on experimental parameters. This provides a basis for rational parameter selection. The approach can be extended to different materials, particle sizes and shapes, and surrounding media under transient heating conditions.</jats:p>