Ion Bombardment-Induced Stress Mechanism for the Formation of Ag Nanotwinned Films on Si Substrates

Nanotwinned face-centered-cubic (FCC) metals have gained significant attention recently due to their exceptional mechanical and electrical properties. Among all the FCC metals, Ag has the lowest stacking fault energy, which allows twin formation to easily occur. In this study, Ag films with a thickness of 4 µm were deposited on Si (100) substrates pre-coated with Ti adhesion layers by electron beam evaporation. With ion beam assistance during the evaporation process, highly (111)-textured and high-density nanotwinned Ag films with excellent properties were produced. Both x-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analyses indicate that the Ag film possesses a strong (111) preferred orientation. In addition, statistical measurements from transmission electron microscopy (TEM) images show that the average twin spacing in nanotwinned Ag films with a deposition rate of 1.8 nm/s is only 6.1 nm. However, conventional models based on thermodynamics are insufficient to describe the formation of growth twins in an ion beam-assisted deposition system. Therefore, an ion bombardment stress model is introduced in this work. The results of the mechanism of deformation twinning are also discussed.