(Table 2) Silicon isotope data for sponge spicules from ODP Hole 113-689B

The silicon isotope composition (d30Si) of biogenic opal provides a view of the silica cycle at times in the past. Reconstructions require the knowledge of silicon isotope fractionation during opal biomineralization. The d30Si of specimens of hexactinellid sponges and demosponges growing in the modern ocean ranged from -1.2 per mil to -3.7 per mil (n = 6), corresponding to the production of opal that has a d30Si value 3.8 per mil +/- 0.8 per mil more negative than seawater silicic acid and a fractionation factor (a) of 0.9964. This is three times the fractionation observed during opal formation by marine diatoms and terrestrial plants and is the largest fractionation of silicon isotopes observed for any natural process on Earth. The d30Si values of sponge spicules across the Eocene-Oligocene boundary at Ocean Drilling Program Site 689 on Maud Rise range from -1.1 per mil to -3.0 per mil, overlapping the range observed for sponges growing in modern seawater.

Tunable mechanical resonator with aluminum nitride piezoelectric

The electromechanical response of piezoelectrically-actuated AlN micromachined bridge resonators has been characterized using laser interferometry and electrical admittance measurements. We compare the response of microbridges with different dimensions and buckling (induced by the initial residual stress of the layers). The resonance frequencies are in good agreement with numerical simulations of the electromechanical behavior of the structures. We show that it is possible to perform a rough tuning of the resonance frequencies by allowing a determined amount of builtin stress in the microbridge during its fabrication. Once the resonator is made, a DC bias added to the AC excitation signal allows to fine-tune the frequency. Our microbridges yield a tuning factor of around 88 Hz/V for a 500 ?m-long microbridge.

Integration of III-V materials on Silicon Substrates for Multi-junction Solar Cell Applications

The work presented here aims to reduce the cost of multijunction solar cell technology by developing ways to manufacture them on cheap substrates such as silicon. In particular, our main objective is the growth of III-V semiconductors on silicon substrates for photovoltaic applications. The goal is to create a GaAsP/Si virtual substrates onto which other III-V cells could be integrated with an interesting efficiency potential. This technology involves several challenges due to the difficulty of growing III-V materials on silicon. In this paper, our first work done aimed at developing such structure is presented. It was focused on the development of phosphorus diffusion models on silicon and on the preparation of an optimal silicon surface to grow on it III-V materials.