Dynamics porous silicon

Recent applications of FNS include the dynamics of the electrical potential fluctuation in an electromembrane system [iv], analysis of the fluctuations of the electrical current in electrochemically deposited conducting polymers [v], and forecasting electrical breakdown in porous silicon [vi]. 

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

Non-Debye dielectric relaxation in porous systems is another example of the dynamic behavior of complex systems on the mesoscale. The dielectric properties of various complex multiphase systems (borosilicate porous glasses [153-156], sol-gel glasses [157,158], zeolites [159], and porous silicon [160,161]) were studied and analyzed recently in terms of cooperative dynamics. The dielectric response in porous systems will be considered here in detail using two quite different types of materials, namely, porous glasses and porous silicon. 

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Bottom-up strategies, which employ silicate precursors, such as tetraethoxysi-lane (TEOS), produce porous silicon dioxide. Silicon dioxide is a much more chemically stable interface than silicon, and precludes some forms of surface functionalization, such as carbonization, which is used to tune particle properties. Additionally, bottom-up approaches are hmited to the production of either spherical or ellipsoid particles, unless used in conjunction with top-down lithography. Shape has been shown fundamentally to determine several properties of the particle that are relevant for drug deUvery, such as flow dynamics, margination, degradation rate and cell uptake [21, 22]. For these reasons, top-down approaches to the production of pSi for biomedical applications have been historically favored. 

Poisoning and thermal aging are the main reason why the lambda characteristic and dynamics of the sensor changes with lifetime [1, 31-33]. Plugging of the porous electrode protective layer by oil, ash, or silicon oxide favors the diffusion of hydrogen to the electrode, which leads to a lean shift in the static characteristic curve [31]. 

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