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Optical sensing of chemical compounds using porous silicon devices In this section are presented some very interesting results about the detection of chemical compounds by using porous silicon optical devices. Some porous silicon structures, were exposed to several substances of environmental interest: the detection in aqueous and humic solutions of a common pesticide and organic compounds. Very large red shifts of the reflectivity spectra, due to changes in the average refractive index, have been observed.
Introduction to the sensing mechanism In this section, are presented optical sensors, based on porous silicon (PSi) technology for liquid and vapour detection. Optical sensors for chemical contaminants can adopt a spectroscopic method (usually in the IR region where gas absorption spectra have specific signatures), or measure the changes in some physical properties (colour, refractive index, photoluminescence, fluorescence and so on) due to the interaction between the substances under investigation and the sensor itself [1, 2]. From this point of view, PSi is a very interesting material due to its large specific surface area (on the order of 500 m 2 /cm 3 ) which is a great advantage in gas sensing applications, so that this technology has been extensively stu<strong>di</strong>ed in this field. When the PSi is exposed to vapours, or <strong>di</strong>p in liquid substances, a repeatable and completely reversible change in the reflectivity spectrum is observed. In fact, the substitution of air in the pores by the organic molecules causes an increasing of the average refractive index of the device, shifting towards longer wavelengths its characteristic reflectivity spectrum. In a first optical characterization, it was followed the approach of Sailor et al. [3] choosing the simple case of a single layer of porous silicon as transducer device. Figure 1 shows a typical reflectivity spectrum (before and after chemical infiltration) from a PSi layer under white light illumination. Reflectance (a.u.) 1.00 0.75 0.50 0.25 1.00 0.75 0.50 after infiltration 0.25 11000 12000 13000 14000 15000 16000 17000 Wavenumber (cm -1 ) Maximum order ( Δm) 16 14 12 10 8 6 4 2 11000 12000 13000 14000 15000 16000 17000 PSi as etched Wavenumber (cm -1 ) n xyl d=27352 (92) nm n unp d=24560 (110) nm Figure 1. Reflectivity spectrum of PSi layer. In the inset the m-order peak are plotted as function of the wavenumber. From the optical point of view, this structure is an optical Fabry-Perot interferometer, so that the maxima in the reflectivity spectrum appear at wavelengths λm which satisfy the fallowing relationship: m = 2 nd / λ (1) m where m is an integer, d is the film thickness and n is the average refractive index of the layer [4, 5]. If it’s assumed that the refractive index is independent on the wavelength over the considered range, the maxima are equally spaced in the wavenumber (1/λm). When the maximum order m is plotted as a function of the wavenumber, each point lies on a straight 22
Page 1: BIOCHIP AND LAB-ON-CHIP FOR GENOMIC
Page 5: The most beautiful thing we can exp
Page 8 and 9: SUMMARY There is no other inorganic
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Page 12 and 13: del silicio coinvolge due portatori
Page 14 and 15: I sensori ottici basati sul silicio
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Page 37 and 38: Reflectivity (a.u.) 160 140 120 100
Page 39 and 40: 23. Anderson SHC, Elliot H, Wallis
Page 41 and 42: phys. stat. sol. (c) 4, No. 6, 1966
Page 43 and 44: 1968 L. De Stefano et al.: Optical
Page 45: 1970 L. De Stefano et al.: Optical
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Page 51 and 52: phys. stat. sol. (c) 4, No. 6 (2007
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Page 59 and 60: • Oxidation of porous silicon Wit
Page 61 and 62: DNA Optical Detection Based on Poro
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Abstract Physica E 38 (2007) 188-19
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190 surface through Si-C bonds. We
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192 Acknowledgments The authors are
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Introduction: PSi hybrid systems Mu
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8. S.H.C. Anderson, H. Elliot, D.J.
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A polymer modified PSi optical devi
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The polymer solutions were prepared
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5 CREATED USING THE RSC ARTICLE TEM
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5 10 15 20 25 30 35 The HFB biofilm
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5 10 15 20 25 Conclusions We have d
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Introduction to Lab-on-chip technol
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• Glass etching The technology fo
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Many lab-on-chip applications have
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Microsystems Based on Porous Silico
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Sensors 2006, 6 681 optical microca
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Sensors 2006, 6 683 changed with a
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Sensors 2006, 6 685 probably exists
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Sensors 2006, 6 687 6. Obermeier, E
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PUBLICATIONS: J1. Luca De Stefano,
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P12. L. De Stefano, L. Rotiroti, I.
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C18. L. De Stefano, I. Rea, L. Roti
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Appendix
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White light source Gas channels Sea
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% Reflectance 110 100 90 80 70 60 5
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IOP PUBLISHING JOURNAL OF PHYSICS:
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J. Phys.: Condens. Matter 19 (2007)
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with a number of other sugar-bindin
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treatment in the range 600-800 nm,
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Sensors 2008, 8, 1-x manuscripts; D
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Sensors 2008 3 2. Experimental A hi
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Sensors 2008 5 Figure 3. Resonant p
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Sensors 2008 7 Figure 6. Resonance
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