p-type porous-silicon transducer for cation detection : effect of the porosity, pore morphology, temperature and ion valency on the sensor response and generalisation of the Nernst equation

• Published in: Applied physics. A, Materials science & processing Vol. 73; no. 5; pp. 585 - 593
• Main Authors: ZAIRI, S, MARTELET, C, JAFFREZIC-RENAULT, N, VOCANSON, F, LAMARTINE, R, M'GAÏETH, R, MAAREF, H, GAMOUDI, M
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.11.2001
• Subjects: Analytical chemistry; Cations; Chemistry; Electrodes; Exact sciences and technology; General equipment and techniques; General, instrumentation; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Morphology; Nanostructure; Physics; Polystyrene resins; Porosity; Sensors; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Transducers; Chemical sensors; Transducers; Sensitivity analysis; Porous materials; Theoretical study; Calixarene; Experimental study; Sensor materials; Layer thickness; Ion detection; Cations; Oxidation; Silicon; Modified material
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s003390100824

This paper shows the possibility of using oxidised porous silicon (PS) as a transducer material for ion-sensor applications. It aims to study the over-Nernstian behaviour of the porous electrodes towards the concentration of cations in contact. The dependence of the sensitivity on the porosity of the samples prepared from highly doped substrates has been studied. Maximal values of over-Nernstian sensitivities around 240 mV/pNa and ~92 mV/pCu, corresponding to a PS-layer porosity of about 65%, obtained respectively from p and p silicon substrates, have been registered. Furthermore, the effect of the porous nanostructure morphology has been studied, by preparing PS samples from weakly doped wafers. The porous-silicon-based sensor behaviour for different PS-layer thicknesses has also been experimentally investigated. According to these results, a physical model has been proposed to explain the mechanisms which govern the charge-carrier transfer from one side to the other of the functionalised oxide layer, and leads to the over-Nernstian adsorption of the cationic species at the electrolyte/SiO2 interface. Afterwards, the Nernst relation has been generalised accordingly, on one hand, to the previous experimental results, and on the other hand, to the results obtained about the ion-valency and the electrolyte-temperature effects on the sensor responses.