Optothermal Raman analysis of thermal conductance and boundary resistance in a subwavelength single nanoparticle

We present optothermal Raman spectroscopy as a powerful technique for characterizing the thermal properties of individual subwavelength nanoparticles. This method enables the extraction of the intrinsic thermal conductance of an individual nanoparticle with an average size representative of the inclusion population and the thermal resistance at the interface between the nanoparticle and its surrounding matrix. By overcoming the spatial resolution limitations of conventional techniques, such as scanning thermal microscopy, and eliminating the need for complex nanoscale heat transfer modeling, optothermal Raman spectroscopy provides direct, size-independent measurements with high accuracy. The technique involves measuring the thermal conductance of target nanoparticles embedded in a matrix of smaller, low-density particles at varying mass fractions. These measurements are then fitted to the effective medium theory to extract both the intrinsic thermal conductance and boundary thermal resistance of the nanoparticles. Validation studies were conducted on monoclinic gallium oxide (β-Ga₂O₃, 590 nm) and zinc oxide (ZnO, 500 nm) particles in a granular silicon matrix, as well as silicon (Si, 100 nm) nanoparticles in a granular carbon matrix. The β-Ga₂O₃ and ZnO particles, with bulk-like thermal properties, served as benchmarks, while the Si nanoparticles exhibited size-dependent thermal behavior. Measurements relied on the resonance frequency of Si as a precise thermometric signal, and results were corroborated by first-principles calculations. By providing direct, reliable measurements without intricate modeling, optothermal Raman spectroscopy offers significant advantages for thermal property characterization. This versatile technique holds great promise for advancing research in materials science and nanotechnology.