Photothermal conversion and laser-induced transformations in silicon–germanium alloy nanoparticles

Si$_{1-x}$Ge$_x$ alloy nanoparticles with controlled composition have been obtained by nanosecond laser ablation of silicon–germanium targets in isopropanol. The synthesized product exhibits a polycrystalline structure and a unimodal size distribution with a predominant content of microparticles and retains the stoichiometry of the composition of the targets used for the synthesis. Nanothermometry with the detection and analysis of a Raman signal from single alloy nanoparticles with a size of $\sim$ 200 nm demonstrates a threefold increase (in comparison with nanoparticles of pure silicon) in the heating efficiency of a nanomaterial with the composition Si$_{0.45}$Ge$_{0.55}$ by 785-nm laser radiation falling into the first “transparency window” of biological tissues. Stimulated by continuous infrared radiation, the diffusion of silicon atoms to the surface (when heated to 650 K) and their oxidation lead to the gradual transformation of alloy nanoparticles into germanium clusters encapsulated in a SiO$_x$ matrix.