Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics

Abstract

Light absorption and scattering of plasmonic metal nanoparticles can lead to non-equilibrium charge carriers, intense electromagnetic near-fields, and heat generation, with promising applications in a vast range of fields, from chemical and physical sensing to nanomedicine and photocatalysis for the sustainable production of fuels and chemicals. Disentangling the relative contribution of thermal and non-thermal contributions in plasmon-driven processes is, however, difficult. Nanoscale temperature measurements are technically challenging, and macroscale experiments are often characterized by collective heating effects, which tend to make the actual temperature increase unpredictable. This work is intended to help the reader experimentally detect and quantify photothermal effects in plasmon-driven chemical reactions, to discriminate their contribution from that due to photochemical processes and to cast a critical eye on the current literature. To this aim, we review, and in some cases propose, seven simple experimental procedures that do not require the use of complex or expensive thermal microscopy techniques. These proposed procedures are adaptable to a wide range of experiments and fields of research where photothermal effects need to be assessed, such as plasmonic-assisted chemistry, heterogeneous catalysis, photovoltaics, biosensing, and enhanced molecular spectroscopy.

Non-Absorbing Dielectric Materials for Surface-Enhanced Spectroscopies and Chiral Sensing in the UV

“…Metal-based nanostructures enhance near-fields intensity with inherent heating of the structure and its surroundings due to their high resistive losses [ 2 , 28 , 29 , 30 ]. Therefore, they are interesting for applications where heating is desired or at least this is not an issue [ 29 , 30 , 31 ]. It is important to note that heating effects are detrimental in many ways for spectroscopic measurements.…”

“…It is important to note that heating effects are detrimental in many ways for spectroscopic measurements. The temperatures generated when the plasmonic resonances are excited can reach up to several hundreds of degrees Kelvin [ 2 , 31 , 32 , 33 ]. These temperatures are high enough to generate substantial changes in the nanomaterial and environment such as deformation or even melting of nanostructures, vaporizing the solvent, refractive index changes through the thermo-optic effect and molecular changes in the samples [ 32 , 33 ].…”

Controlling Light, Heat, and Vibrations in Plasmonics and Phononics

“…Plasmonic systems have been attracting a wide interest across different fields mainly due to their ability to concentrate electromagnetic energy down to volumes well below the diffraction limit thus reaching nanoscale dimensions. [40,41] This characteristic has led to a variety of applications, embracing spectroscopy, [42] molecular sensing, [43] photovoltaics, [44,45] nanoantennas, [46] nanochemistry, [15,16,47] medical applications, [10,[48][49][50] and desalination devices. [51][52][53]…”

“…[9] While detrimental for some applications, controlled nanoscale heat generation can be a key enabler for many thermoplasmonic applications, as explored in the fast growing fields of nanomedicine, [10,11] nanobiology, [12] and nanochemistry. [13][14][15][16] In this scenario, thermoplasmonics [17] focuses on the possible strategies for an efficient heat generation while phononics [18] dedicates itself especially to the phonon manipulation. [19][20][21] Additionally, the fact that both thermoplasmonics and phononics ultimately harness the same kind of particle, results in a further push for the identification of structures or devices capable of exploiting the particle/wave dual nature associated to phonons.…”

Plasmon-generated hot holes for chemical reactions

“…These three effects usually contribute to the plasmon-mediated chemical reactions simultaneously. It is difficult, sometimes impossible, to distinguish the individual contribution of each effect, even though many attempts have been made in the past few years [26][27][28][29].…”