Nanoscale ion-beam mixing in Au-Si and Ag-Si eutectic systems

MeV ion induced mixing in the nanoscale regime for Au and Ag nanoislands on silicon substrates has been studied. Au and Ag nanoislands are grown on silicon substrates at room temperature and irradiated with 1.5-MeV Au2+ ions at various fluences. Cross-sectional high-resolution transmission electron microscopy and Rutherford backscattering spectrometry (RBS) are used to study the ion-beam mixing in Au/SiOx/Si and Ag/SiOx/Si systems. We observe a metastable mixed phase for the Au-Si system at a fluence of 1 X 10(14) ions cm(-2), while no mixed phase is formed for the Ag-Si system. For both Au-Si and Ag-Si systems, a part of the islands is pushed into the substrate. The mixed phase of the Au-Si system is found to be crystalline in nature. The higher eutectic temperature and lower heat of mixing of the Ag-Si system compared to the Au-Si system could be responsible for the lack of mixing and silicide formation in the Ag-Si system.