The elastic properties of materials composed of thin laminar structures control a broad range of phenomena in diverse systems. For example, elasticity affects the response of tissues in the eye that control the focusing of light, while strains within nano-scale films and coatings in the next generation of microelectronic devices could have profound effects on their functionality. Measurement of the elastic properties of such microscale structures has however proven difficult with traditional techniques such as mechanical stretching and nanoindentation being ineffective at these spatial length scales. In this thesis, Brillouin light scattering is shown to offer an effective approach to accurately measure the elastic properties of transparent tissues within the eye as well as dielectric thin films of interest to the semiconductor industry.
As the human eye ages, focusing on a near object generally becomes difficult - a condition known as presbyopia. An age related stiffening of lens mechanical properties has been suggested as a cause for the onset of presbyopia. High frequency (GHz) Brillouin light scattering (BLS) experiments were performed on human lenses spanning an age range from 30-70 years. The measured frequency shifts, and derived bulk moduli values were found to
not change significantly over the age span studied suggesting the human eye lens does not appreciably stiffen with aging. In addition, similar high frequency studies on the cornea were performed with Brillouin light scattering (BLS) and quantitative ultrasound spectroscopy
(QUS) that were complimented with low frequency (<5 Hz) dynamic mechanical analysis (DMA). Intact bovine eye globes were also studied with BLS at low power levels, allowing the stiffness of the transparent cornea and lens tissues to be mapped ex-vivo as a function of axial depth. These findings demonstrate the potential of utilizing BLS for clinical applications.
Scaling down the material components used in microelectronic interconnects presents increasing challenges to technology development in the semiconductor industry. To reduce RC time delays, low dielectric constant (k) hybrid organic-inorganic carbon doped SiO2 (SiOC:H) and amorphous carbon (a-C:H) interconnect layers with controlled levels of porosity have been pursued. However, increased porosity coupled with reduced film thicknesses (<100nm) could potentially reduce device functionality. Nanoscale film thicknesses
render techniques such as nano-indentation to be ineffective to characterize the mechanical properties of these highly compact and porous structures. Brillouin light scattering from localized acoustic excitations enable the independent elastic constants, and thus the mechanical properties, of dielectric films with thicknesses as low as 94 nm and porosity levels up to 45%. The frequency dispersion and associated light scattering intensities of longitudinal and transverse acoustic standing mode type excitations were observed. The Poisson’s ratio (¿¿) and Young’s Modulus (E)of these highly porous low-k materials were determined and compared to those of conventional SiO2 and non-porous low-k materials.