Spatial stress distribution and optical properties of GaN films grown on convex shape-patterned sapphire substrate by metalorganic chemical vapor deposition

μ-Raman and μ-photoluminescence methods have been employed to investigate microscopic spatial stress distribution and optical properties of GaN films grown on the convex shape-patterned sapphire substrate (CSPSS). By comparison of the μ-Raman and μ-PL spectra, we found that significantly large difference, Δσ_xx ∼0.46 GPa, in biaxial compressive stress between the flat trench and convex regions in the side facet of the GaN film, around ∼2 μm below the surface whereas on the GaN surface, little difference with large residual stress was observed in both regions compared to those from the side facet. Temperature dependent and time-resolved photoluminescence spectra have shown that the GaN film grown on the CSPSS has improved crystal purity through the reduction of intrinsic point defects.     

Effect of linearized contact spring in track dynamic system

In recent years, a number of researches into dynamic characteristics of the noise and vibration in the railway have been performed. Since the high frequency vibration, which occurs in the irregularity(roughness) of the wheel and rail running surfaces, causes the track noise in railway system, analytic study with measurement of the vibration for the wheel and rail is needed. So, the algorithm and program for the vibration analysis in the track system were developed as a part of the analytic study. In this study, evaluation for the effect of the linearized contact spring in track dynamic system was studied with the developed program. In addition, analytical study for the comparison between hysteretic and viscous damping in this system was performed. The result shows that both the linearized contact spring stiffness and damping of track system are important factors in track dynamic analysis model.