Microscopic analysis of thermally-driven formation of Cu-Si alloy nanoparticles in a Cu/Si template

Selective thermal diffusion of Cu into a 100-nm-thick SiO2-patterned Si(001) substrate was investigated to elucidate the spontaneous formation of Cu-Si alloy nanoparticles. Transmission electron microscopy and energy dispersive X-ray spectroscopy provided the indirect evidence for the formation on the substrate’s surface of nanoparticles that served as a catalyst to grow SiO2 nanowires selectively in window regions. The microstructural analysis revealed that thermal annealing caused selective diffusion of Cu into the Si matrix in window regions only and that the Cu-Si alloy nanoparticles were formed at 900 °C although the diffusion of Cu into Si was already significant at 700 °C. The nanoparticles that were sparsely distributed below the surface of the Si matrix did not serve as a catalyst for growing SiO2 nanowires, and the chemical composition analysis showed that the nanoparticles at the tip of SiO2 nanowires were Cu3Si.