A protein microarray has been realized on a porous silicon (PS) chip by means of electron beam irradiation using a
standard SEM equipped with a nanopattern generator system. Two proteins have been used to generate the array: the
glucose-binding protein (GBP) and the glutamine-binding protein (GlnBP), both isolated from Escherichia coli.
The proteins functionality have been tested by means of a competitive assay.
Fluid-solid interfacial phenomena are a subject of much interest. In the adsorption phenomena, the adsorbent experiences the action of the molecular forces inducing strains.
In this paper, we experimentally investigate adsorption phenomena in porous silicon microcavities by spontaneous Raman scattering. Polarised Raman spectra are measured in a backscattering configuration using a diode laser at 404 nm. We observe a reversible blue shift of the Raman spectra exposing a porous silicon multilayer to air saturated with vapor of pentane or iso-propanol. We ascribe the shift of the Raman spectra to the strain in porous silicon due to the adsorption in the pore walls.
There have been many papers reporting visible luminescence and light emission at 1.54 micron, at room temperature, from porous silicon (Psi) and from Erbium doped Psi, respectively. These results have stimulated a great deal of excitement, because they suggest the possibility of a silicon based optoelectronics technology.
In this paper, in order to generate radiation at 1.54 micron in Psi, a diffferent approach based on Raman scattering is presented. This approach has important advantages: no special impurities are required, so samples realisation is simple and chip; moreover enhancement of Raman scattering and nonlinear effects in nanostructured porous silicon could be experienced. Finally preliminary experimental results of Raman emission in porous silicon at 1.54 micron are reported.
Recently, an increasing interest has been devoted to the use of porous silicon (p-Si) in photonics and in sensing fields. In particular, the great reactivity, mainly due to its large surface to volume ratio, has demonstrated to be promising in sensing applications for the detection of gases, vapors, and biochemical molecules. In this work, we present experimental and numerical results on p-Si optical microcavities as sensing transducers in biological and chemical fields. The measures are based on the change of the cavity reflectivity spectrum induced by the exposition to the bio-chemical specimen under test. The p-Si microcavity has a Fabry-Pèrot structure confined between two Distributed Bragg Reflectors (DBRs) with high reflectivity in the wavelength range of interest. The DBRs have been obtained modulating the porosity, therefore the refractive index, of p-Si layers during the silicon electro-chemical etching process. The optical thickness (nd) of each single-layer forming the DBR is l/4, where d is the layer physical thickness, n its refractive index and l is the Bragg wavelength. A l/2-thick layer placed between the top and bottom DBRs works as a microcavity resonating at the Bragg wavelength l. The realized sensors operate at the fiber optic communication wavelength of 1.55 mm. A complete experimental characterization of the devices as vapor and liquid sensor is reported. An analytical model, allowing the correct interpretation of the sensing dynamics, is also reported and discussed. Finally, preliminary results concerning DNA-probe immobilization in p-Si pores and consequent recognition of complementary DNA strands are presented.
An easy and effective technique for locally oxidize, melt or remove Porous Silicon layers is presented and discussed. The method takes advantage from the very low thermal conductivity of Porous Silicon. With the aid of a focused laser beam, it is possible to reach temperatures of several hundreds °C at the illuminated spot. Results on fabrication of all-porous planar waveguides are presented and discussed. Preliminary results on the application of this technique for fabricating 2D and 3D photonic crystals are reported.
On exposure at different chemical substances several physical quantities of porous silicon, such as reflectivity,
photoluminescence, and electrical conductivity, change drastically. In particular, we have used porous silicon microcavities as chemical sensors, measuring resonant peak shifts in the reflectivity spectra due to capillary condensation of the vapor in the silicon pores. Understanding sensor behaviour depends on the dielectric function model and on the interaction mechanism assumed. With proper choices, we can also quantitatively characterize the Porous Silicon Microcavity sensing device features.
Porous silicon (PS) has been known for quite a long time for its photoluminescence and for its usage as a sensing element. However, only in recent years this material has been proposed as a substrate for integrated optoelectronic devices and, despite the low fabrication costs and the possibility to tailor the refractive index varying the material porosity, its usage is still at the very beginning. In this paper we present the fabrication of integrated waveguides in PS and we describe our efforts to reduce the propagation losses. Different fabrication approaches have been studied: the first one uses selective anodization to obtain layers with different porosity and thus different refractive index. Another one exploits the different oxidation grades of the various porous layers to fabricate dense oxidized porous silicon waveguides. A detailed characterization of the obtained waveguides is reported. In particular, propagation losses as low as 7 dB/cm have been obtained in simple non-optimized multimode planar waveguides at the optical communication wavelength of 1.55 micrometers . This encouraging result paves the way to the next realization of porous silicon-based integrated optical devices for communication and sensing purposes. Finally, the results concerning a completely new approach, based on a laser ablation technique, to define the rib structure of porous silicon channel waveguides is presented.