Is phytoextraction a suitable green treatment for metal-contaminated sediments ?

International audienceThe cleaning of waterways by regular dredging generates great volumes of sediments and, owing to human activities, these sediments often contain large amounts of metals. These materials are usually spread on landfill sites. Phytoremediation could be a stategy for the reclamation of these polluted sediments. To our knowledge, phytoextraction with hyperaccumulating plants has been few tested on contaminated sediment. This work focuses on the mechanisms of Cd accumulation in Arabidopsis halleri, a Cd and Zn hyperaccumulator, and the effects of this species on a metal polluted sediment

Low-Wavelengths SOI CMOS Photosensors for Biomedical Applications

INTRODUCTION : Biological agents may be characterized (in terms of quantity (or concentration), purity, nature) using optical ways like spectrometry, fluorometry and real-time PCR for example. Most of these techniques are based on absorbance or fluorescence. Indeed, many biological molecules can absorb the light when excited at wavelengths close to blue and ultraviolet (UV). For example, DNA, RNA and proteins feature an absorption peak in the deep UV, more precisely around 260 and 280 nm (Karczemska & Sokolowska, 2001). This work is widely focused on those wavelengths. A biological sample concentration measurement method can be based on UV light absorbance or transmittance, as already known and realized with high-cost and large-size biomedical apparatus. But, often, the difficulties come from the limitation for measuring very small concentrations (close to a few ng/µL or lower) since the measurement of such small light intensity variations at those low wavelengths requires a precise light source, and very efficient photodetectors. Reducing the dimensions of such a characterization system further requires a small light source, a miniaturized photosensor and a processing system with high precision to reduce the measurement variations. Some light-emitting diodes (LED) performing at those UV wavelengths have recently appeared and may be used to implement the light source. Concerning the optical sensor, while accurate but high-cost photosensors in technologies such as AlGaN and SiC provide high sensitivities in UV low wavelengths thanks to their semiconductor bandgap (Yotter & Wilson, 2003), the silicon-on-insulator (SOI) layers absorb the photons in that specific range thanks to an appropriate thickness of the silicon. Adding excellent performances of low power consumption, good temperature behavior and high speed (Flandre et al., 1999; 2001), the SOI technology allows the designers for integrating a specific signal processing integrated CMOS circuit to transform the photocurrent into a digital signal for example. This opens the possibility to build a low-cost, complete and portable microsystem, including the light source, the photodetector and a recipient for the sample to characterize […

Silicon-on-insulator optoelectronic components for micropower solar energy harvesting and bio-environmental instrumentation

This work presents an analysis of optoelectronic components fabricated in silicon-on-insulator (SOI) technology. On one hand, the thesis focuses on UV sensors (λ < 400nm) for bio-environmental applications and on the other hand, it studies CMOS integrated photovoltaic cells for micropower solar energy harvesting. The SOI technology features a thin Si film into which lateral PIN photodiodes are optimized. The responsivity is modeled to optimize the spectral response in UV by adequate choices of anti-reflection coatings. Other structures based on silicon-on- nothing and membrane technologies are investigated. A current-to-frequency integrated circuit is designed to interface the UV photodiodes for bio-environmental instrumentation. The circuit consumes a total power of 27μW and is linear with respect to the responsivity of the photodiode. An optical range of 6 decades can be reached if the power consumption is increased. The SOI photosensors are used to quantify the concentration of biological material by UV transmittance. The UV source is implemented by a low wavelength LED which directly illuminates the sample contained either in PCR tubes, or in well microplates or in PDMS channel. The best result is achieved with the complete UV photosensor for which DNA is quantified on a range from 400ng/μL to 40fg/μL, within PCR microtubes. Other measurements performed in PDMS channel are very promising for future co-integration and microsystems. The SOI substrate is also used to integrate novel lateral solar cells, embedded under the buried oxide. Efficiencies of 10% and 15% are reached for ungated diodes for outdoor and indoor irradiances respectively. Gated diodes reach efficiencies of 12% and 22% for the same irradiances and for a maximal frontgate voltage. A lumped-element modeling is also presented for circuit simulator integration. Finally, it is proved that miniaturized SOI solar cells can be designed for supplying various specific integrated circuits with very small die areas.(FSA 3) -- UCL, 201

Temperature and Silicon Film Thickness Influence on the Operation of Lateral SOI PIN Photodiodes for Detection of Short Wavelengths

This work presents an analysis of the temperature influence on the performance of a lateral thin-film SOI PIN photodiodes when illuminated by low wavelengths, in the range of blue and ultra-violet (UV). Experimental measurements performed from 100K to 400K showed that the optical responsitivity of SOI PIN photodetectors is affected by temperature change, being reduced at low and moderately high temperatures. Two-dimensional numerical simulations showed the same trends as in the experimental results, and were used both to investigate the physical phenomena responsible for the observed behavior as a function of the temperature as well as to predict the influence of silicon film thickness downscaling on the photodetector performance

High-efficiency solar cell embedded in SOI substrate for ULP autonomous circuits

A low-cost and high-efficiency monocristalline silicon solar cell embedded in a CMOS circuit is proposed for ULP autonomous circuits. Based on a SOI wafer, a photovoltaic lateral diode is realized in the substrate using the fabrication steps of the FD SOI CMOS process of the superposed active circuitry. In case of front side illumination, we achieve 15% efficiency when no CMOS circuit is present, and 11% with an integrated structure in the silicon thin-film overlayer. An efficiency of 19.5% can be further reached in this last case when a 20 V bias difference is applied between the thin-film layer and the back contact to deplete the buried oxide / Si substrate interface.Anglai

Complete Microsystem Using SOI Photodiode for DNA Concentration Measurement

In this paper, we describe a complete microsystem allowing the measurement of DNA concentration based on ultraviolet (UV) absorption. The system includes an ultraviolet light-emitting diode (LED) as light source and a silicon-on-insulator (SOI) lateral PIN diode as photodetector. After demonstrating the feasibility of the system with a quartz container, measurements are performed on DNA samples in PCR tubes by direct transmittance. The measurement of the sample in the tubes implies no waste neither manipulation of the samples. We study the impact of variation of the different parameters of the system, i.e. the wavelength of the LED, the light power reaching the samples and the bias of the photosensor. We are able to measure responses for DNA concentrations in the range from 400 ng/μL to 4 pg/μL and correlate bacteria concentrations to the induced photocurrent of the diode from 6.1011 spores/mL to 6.107 spores/mL. The system features a present precision of current measurements of 2%. In the optimal case, a limit of detection (LOD) of 0.02 ng/μL has been estimated