Investigation of the near surface mechanical properties of gold-silicon thin films

An investigation of the material properties of polycrystalline Au films and the effect of Si content on the material properties and structure of co-evaporated Au-Si films has been performed. Atomic Force Microscopy (AFM), nanoindentation and four-point probe were utilized to investigate the surface topography, mechanical and electrical properties of these films, respectively. X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) measurements were performed to investigate the material crystallography and structure.;The hardness of pure Au films was found to be approximately 1.2 GPa and increased by about 40--80% (1.64 GPa--2.13 GPa) by the addition of 2.5 and 6 at. % Si, respectively and approximately 102% to 2.41 GPa by the addition of 21 at. % Si. The film resistivity increased nearly linearly from 5.58--38.15 microO-cm as the Si content increased from 2.5--21 at. %, respectively.;XRD measurements on the Au/21 at. % Si film suggested the formation of an unknown crystalline Au-Si phase. The metastability of this phase was shown experimentally by performing a second XRD measurement on the same specimen after an 8 week room temperature storage period which indicated that the unknown Au-Si surface phase present had almost completely dissociated. The hardness and reduced elastic modulus decreased by approximately 32% from 2.41--1.65 GPa and 53% from 88--41.5 GPa, respectively.;TEM measurements, conducted on an Au/25 at. % Si specimen, showed the nanocrystalline grain structure of the Au, with an average grain size of 18 nm (consistent with the XRD measurement), with a dispersion of amorphous Si particles approximately 1--5 nm in diameter. From these results, the predicted hardness increase of the Au-Si film resulting from the Orowan hardening mechanism was estimated to be HOrowan ≈ 0.05 GPa--1.07 GPa representing approximately 4--88% of the overall hardness increase measured for the Au/21 at. % Si film assuming the same Si content for the TEM specimens. The estimated HOrowan range suggested that additional mechanisms, such as the Hall-Petch effect, may be responsible for the measured hardness increase.