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The human ocular lens is a tissue capable of changing its shape to dynamically adjust the optical power of the eye, a function known as accommodation, which gradually declines with age. This capability is the response of the lens tissue to external forces which, in turn, is modulated by the biomechanical characteristics of lens tissues. In order to investigate the contributions of lens sclerosis to loss of accommodation, we report on in vitro confocal Brillouin light scattering studies of human ocular lenses spanning over a 30-70 year age range. Using this non-destructive measurement method, we determined that the longitudinal bulk modulus (average ± SD) of the lens nucleus (2.79±0.14 GPa) was consistently greater than the bulk modulus of the lens cortex (2.36±0.09 GPa). Moreover, our results showed that these differences were not age dependent over the 40 year age range that we evaluated using healthy lens tissues. Our results are consistent with the hypothesis that an age-dependent change in the bulk modulus of lens tissues does not fully account for the natural decline of accommodation.

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Low-k dielectrics have predominantly replaced silicon dioxide as the interlayer dielectric for interconnects in state of the art integrated circuits. In order to further reduce interconnect RC delays, additional reductions in k for these low-k materials are being pursued via the introduction of controlled levels of porosity. The main challenge for such dielectrics is the substantial reduction in elastic properties that accompanies the increased pore volume. We report on Brillouin light scattering measurements used to determine the elastic properties of these films at thicknesses well below 200 nm, which are pertinent to their introduction into present ultralarge scale integrated technology. The observation of longitudinal and transverse standing wave acoustic resonances and their transformation into traveling waves with finite in-plane wave vectors provides for a direct non-destructive measure of the principal elastic constants that characterize the elastic properties of these porous nano-scale films. The mode dispersion further confirms that for porosity levels of up to 25%, the reduction in the dielectric constant does not result in severe degradation in the Young's modulus and Poisson's ratio of the films. V

Integrating nanometre sized pores into hybrid organic-inorganic interconnect layers is one of the key approaches being undertaken by the semiconductor industry to sustain the continued scale down of micro-electronic devices. While increasing porosity of the layers achieves the desirable lowering of the dielectric constant (k), it also has the potential to reduce mechanical and thermal stability and degrade device functionality. We report on Brillouin light scattering to measure the independent elastic constants, and thus the mechanical properties, of ultrathin dielectric films with porosity levels up to 45%, the highest in the industry. Longitudinal and transverse acoustic standing mode type excitations were observed from sub 200 nm thick low-k thin films, and their frequency dispersion and associated light scattering intensities were utilized to determine Poisson's ratio (ν) and Young's modulus (E). In comparison with SiO 2 and non-porous low-k materials, significant modifications were found in ν and E of these highly porous carbon-doped SiO 2 (Si-O-C-H) and amorphous carbon (a-C : H) low-k interlayer dielectrics.