SiGe nanocrystals have been formed in SiO 2 matrix by cosputtering Si, Ge, and SiO 2 independently on Si substrate. Effects of the annealing time and temperature on structural and compositional properties are studied by transmission electron microscopy, x-ray diffraction ͑XRD͒, and Raman spectroscopy measurements. It is observed that Ge-rich Si ͑1−x͒ Ge x nanocrystals do not hold their compositional uniformity when annealed at high temperatures for enough long time. A segregation process leading to separation of Ge and Si atoms from each other takes place. This process has been evidenced by a double peak formation in the XRD and Raman spectra. We attributed this phase separation to the differences in atomic size, surface energy, and surface diffusion disparity between Si and Ge atoms leading to the formation of nonhomogenous structure consist of a Si-rich SiGe core covered by a Ge-rich SiGe shell. This experimental observation is consistent with the result of reported theoretical and simulation methods.

No abstract

Control of residual stress in thin films is critical in obtaining high mechanical quality coatings without cracking, buckling, or delamination. In this work, we present a simple and effective method of residual stress reduction in sputter deposited thin films by stacking low and high material density layers of the same material. This multilayer density modulated film is formed by successively changing working gas pressure between high and low values, which results in columnar nanostructured and dense continuous layers, respectively. In order to investigate the evolution of residual stress in density modulated thin films, we deposited ruthenium (Ru) films using a DC magnetron sputtering system at alternating argon (Ar) pressures of 20 and 2 mTorr. Wafer's radius of curvature was measured to calculate the intrinsic thin film stress of multilayer Ru coatings as a function of total film thickness by changing the number of high density and low density layers. By engineering the film density, we were able to reduce film stress more than one order of magnitude compared to the conventional dense films produced at low working gas pressures. Due to their low stress and enhanced mechanical stability, we were able to grow these density modulated films to much higher thicknesses without suffering from buckling. Morphology and crystal structure of the thin films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A previously proposed model for stress reduction by means of relatively rough and compliant sublayers was used to explain the unusually low stress in the specimens investigated.

No abstract